Use pointer-by-value captures in coroutine test lambdas

Defense-in-depth against a GCC 14 bug where reference captures in
coroutine lambdas are corrupted in the coroutine frame. The root
cause is fixed in CoroTaskRunner::init() (heap storage), but using
explicit pointer captures avoids any residual risk.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

cspell.config.yaml

@@ -71,12 +71,14 @@ words:
   - coldwallet
   - compr
   - conanfile
+  - cppcoro
   - conanrun
   - confs
   - connectability
   - coro
   - coros
   - cowid
+  - cppcoro
   - cryptocondition
   - cryptoconditional
   - cryptoconditions
@@ -99,11 +101,14 @@ words:
   - endmacro
   - exceptioned
   - Falco
+  - fcontext
   - finalizers
   - firewalled
+  - fcontext
   - fmtdur
   - fsanitize
   - funclets
+  - gantt
   - gcov
   - gcovr
   - ghead
@@ -185,6 +190,7 @@ words:
   - ostr
   - pargs
   - partitioner
+  - pratik
   - paychan
   - paychans
   - permdex
@@ -192,6 +198,7 @@ words:
   - permissioned
   - pointee
   - populator
+  - pratik
   - preauth
   - preauthorization
   - preauthorize
@@ -206,6 +213,7 @@ words:
   - queuable
   - Raphson
   - replayer
+  - repost
   - rerere
   - retriable
   - RIPD
@@ -236,6 +244,7 @@ words:
   - soci
   - socidb
   - sslws
+  - stackful
   - statsd
   - STATSDCOLLECTOR
   - stissue

include/xrpl/core/CoroTask.h

@@ -0,0 +1,687 @@
+#pragma once
+
+#include <coroutine>
+#include <exception>
+#include <utility>
+#include <variant>
+
+namespace xrpl {
+
+template <typename T = void>
+class CoroTask;
+
+/**
+ * CoroTask<void> -- coroutine return type for void-returning coroutines.
+ *
+ * Class / Dependency Diagram
+ * ==========================
+ *
+ *   CoroTask<void>
+ *   +-----------------------------------------------+
+ *   | - handle_ : Handle (coroutine_handle<promise>) |
+ *   +-----------------------------------------------+
+ *   | + handle(), done()                             |
+ *   | + await_ready/suspend/resume  (Awaiter iface)  |
+ *   +-----------------------------------------------+
+ *            |  owns
+ *            v
+ *   promise_type
+ *   +-----------------------------------------------+
+ *   | - exception_    : std::exception_ptr           |
+ *   | - continuation_ : std::coroutine_handle<>      |
+ *   +-----------------------------------------------+
+ *   | + get_return_object() -> CoroTask              |
+ *   | + initial_suspend()   -> suspend_always (lazy) |
+ *   | + final_suspend()     -> FinalAwaiter          |
+ *   | + return_void()                                |
+ *   | + unhandled_exception()                        |
+ *   +-----------------------------------------------+
+ *            |  returns at final_suspend
+ *            v
+ *   FinalAwaiter
+ *   +-----------------------------------------------+
+ *   | await_suspend(h):                              |
+ *   |   if continuation_ set -> symmetric transfer   |
+ *   |   else                 -> noop_coroutine        |
+ *   +-----------------------------------------------+
+ *
+ * Design Notes
+ * ------------
+ * - Lazy start: initial_suspend returns suspend_always, so the coroutine
+ *   body does not execute until the handle is explicitly resumed.
+ * - Symmetric transfer: await_suspend returns a coroutine_handle instead
+ *   of void/bool, allowing the scheduler to jump directly to the next
+ *   coroutine without growing the call stack.
+ * - Continuation chaining: when one CoroTask is co_await-ed inside
+ *   another, the caller's handle is stored as continuation_ so
+ *   FinalAwaiter can resume it when this task finishes.
+ * - Move-only: the handle is exclusively owned; copy is deleted.
+ *
+ * Usage Examples
+ * ==============
+ *
+ * 1. Basic void coroutine (the most common case in rippled):
+ *
+ *      CoroTask<void> doWork(std::shared_ptr<CoroTaskRunner> runner) {
+ *          // do something
+ *          co_await runner->suspend();   // yield control
+ *          // resumed later via runner->post() or runner->resume()
+ *          co_return;
+ *      }
+ *
+ * 2. co_await-ing one CoroTask<void> from another (chaining):
+ *
+ *      CoroTask<void> inner() {
+ *          // ...
+ *          co_return;
+ *      }
+ *      CoroTask<void> outer() {
+ *          co_await inner();   // continuation_ links outer -> inner
+ *          co_return;          // FinalAwaiter resumes outer
+ *      }
+ *
+ * 3. Exceptions propagate through co_await:
+ *
+ *      CoroTask<void> failing() {
+ *          throw std::runtime_error("oops");
+ *          co_return;
+ *      }
+ *      CoroTask<void> caller() {
+ *          try { co_await failing(); }
+ *          catch (std::runtime_error const&) { // caught here }
+ *      }
+ *
+ * Caveats / Pitfalls
+ * ==================
+ *
+ * BUG-RISK: Dangling references in coroutine parameters.
+ *   Coroutine parameters are copied into the frame, but references
+ *   are NOT -- they are stored as-is. If the referent goes out of scope
+ *   before the coroutine finishes, you get use-after-free.
+ *
+ *      // BROKEN -- local dies before coroutine runs:
+ *      CoroTask<void> bad(int& ref) { co_return; }
+ *      void launch() {
+ *          int local = 42;
+ *          auto task = bad(local);  // frame stores &local
+ *      }  // local destroyed; frame holds dangling ref
+ *
+ *      // FIX -- pass by value, or ensure lifetime via shared_ptr.
+ *
+ * BUG-RISK: GCC 14 corrupts reference captures in coroutine lambdas.
+ *   When a lambda that returns CoroTask captures by reference ([&]),
+ *   GCC 14 may generate a corrupted coroutine frame. Always capture
+ *   by explicit pointer-to-value instead:
+ *
+ *      // BROKEN on GCC 14:
+ *      jq.postCoroTask(t, n, [&](auto) -> CoroTask<void> { ... });
+ *
+ *      // FIX -- capture pointers explicitly:
+ *      jq.postCoroTask(t, n, [ptr = &val](auto) -> CoroTask<void> { ... });
+ *
+ * BUG-RISK: Resuming a destroyed or completed CoroTask.
+ *   Calling handle().resume() after the coroutine has already run to
+ *   completion (done() == true) is undefined behavior. The CoroTaskRunner
+ *   guards against this with an XRPL_ASSERT, but standalone usage of
+ *   CoroTask must check done() before resuming.
+ *
+ * BUG-RISK: Moving a CoroTask that is being awaited.
+ *   If task A is co_await-ed by task B (so A.continuation_ == B), moving
+ *   or destroying A will invalidate the continuation link. Never move
+ *   or reassign a CoroTask while it is mid-execution or being awaited.
+ *
+ * LIMITATION: CoroTask is fire-and-forget for the top-level owner.
+ *   There is no built-in notification when the coroutine finishes.
+ *   The caller must use external synchronization (e.g. CoroTaskRunner::join
+ *   or a gate/condition_variable) to know when it is done.
+ *
+ * LIMITATION: No cancellation token.
+ *   There is no way to cancel a suspended CoroTask from outside. The
+ *   coroutine body must cooperatively check a flag (e.g. jq_.isStopping())
+ *   after each co_await and co_return early if needed.
+ *
+ * LIMITATION: Stackless -- cannot suspend from nested non-coroutine calls.
+ *   If a coroutine calls a regular function that wants to "yield", it
+ *   cannot. Only the immediate coroutine body can use co_await.
+ *   This is acceptable for rippled because all yield() sites are shallow.
+ */
+template <>
+class CoroTask<void>
+{
+public:
+    struct promise_type;
+    using Handle = std::coroutine_handle<promise_type>;
+
+    /**
+     * Coroutine promise. Compiler uses this to manage coroutine state.
+     * Stores the exception (if any) and the continuation handle for
+     * symmetric transfer back to the awaiting coroutine.
+     */
+    struct promise_type
+    {
+        // Captured exception from the coroutine body, rethrown in
+        // await_resume() when this task is co_await-ed by a caller.
+        std::exception_ptr exception_;
+
+        // Handle to the coroutine that is co_await-ing this task.
+        // Set by await_suspend(). FinalAwaiter uses it for symmetric
+        // transfer back to the caller. Null if this is a top-level task.
+        std::coroutine_handle<> continuation_;
+
+        /**
+         * Create the CoroTask return object.
+         * Called by the compiler at coroutine creation.
+         */
+        CoroTask
+        get_return_object()
+        {
+            return CoroTask{Handle::from_promise(*this)};
+        }
+
+        /**
+         * Lazy start. The coroutine body does not execute until the
+         * handle is explicitly resumed (e.g. by CoroTaskRunner::resume).
+         */
+        std::suspend_always
+        initial_suspend() noexcept
+        {
+            return {};
+        }
+
+        /**
+         * Awaiter returned by final_suspend(). Uses symmetric transfer:
+         * if a continuation exists, transfers control directly to it
+         * (tail-call, no stack growth). Otherwise returns noop_coroutine
+         * so the coroutine frame stays alive for the owner to destroy.
+         */
+        struct FinalAwaiter
+        {
+            /**
+             * Always false. We need await_suspend to run for
+             * symmetric transfer.
+             */
+            bool
+            await_ready() noexcept
+            {
+                return false;
+            }
+
+            /**
+             * Symmetric transfer: returns the continuation handle so
+             * the compiler emits a tail-call instead of a nested resume.
+             * If no continuation is set, returns noop_coroutine to
+             * suspend at final_suspend without destroying the frame.
+             *
+             * @param h Handle to this completing coroutine
+             *
+             * @return Continuation handle, or noop_coroutine
+             */
+            std::coroutine_handle<>
+            await_suspend(Handle h) noexcept
+            {
+                if (auto cont = h.promise().continuation_)
+                    return cont;
+                return std::noop_coroutine();
+            }
+
+            void
+            await_resume() noexcept
+            {
+            }
+        };
+
+        /**
+         * Returns FinalAwaiter for symmetric transfer at coroutine end.
+         */
+        FinalAwaiter
+        final_suspend() noexcept
+        {
+            return {};
+        }
+
+        /**
+         * Called by the compiler for `co_return;` (void coroutine).
+         */
+        void
+        return_void()
+        {
+        }
+
+        /**
+         * Called by the compiler when an exception escapes the coroutine
+         * body. Captures it for later rethrowing in await_resume().
+         */
+        void
+        unhandled_exception()
+        {
+            exception_ = std::current_exception();
+        }
+    };
+
+    /**
+     * Default constructor. Creates an empty (null handle) task.
+     */
+    CoroTask() = default;
+
+    /**
+     * Takes ownership of a compiler-generated coroutine handle.
+     *
+     * @param h Coroutine handle to own
+     */
+    explicit CoroTask(Handle h) : handle_(h)
+    {
+    }
+
+    /**
+     * Destroys the coroutine frame if this task owns one.
+     */
+    ~CoroTask()
+    {
+        if (handle_)
+            handle_.destroy();
+    }
+
+    /**
+     * Move constructor. Transfers handle ownership, leaves other empty.
+     */
+    CoroTask(CoroTask&& other) noexcept : handle_(std::exchange(other.handle_, {}))
+    {
+    }
+
+    /**
+     * Move assignment. Destroys current frame (if any), takes other's.
+     */
+    CoroTask&
+    operator=(CoroTask&& other) noexcept
+    {
+        if (this != &other)
+        {
+            if (handle_)
+                handle_.destroy();
+            handle_ = std::exchange(other.handle_, {});
+        }
+        return *this;
+    }
+
+    CoroTask(CoroTask const&) = delete;
+    CoroTask&
+    operator=(CoroTask const&) = delete;
+
+    /**
+     * @return The underlying coroutine_handle
+     */
+    Handle
+    handle() const
+    {
+        return handle_;
+    }
+
+    /**
+     * @return true if the coroutine has run to completion (or thrown)
+     */
+    bool
+    done() const
+    {
+        return handle_ && handle_.done();
+    }
+
+    // -- Awaiter interface: allows `co_await someCoroTask;` --
+
+    /**
+     * Always false. This task is lazy, so co_await always suspends
+     * the caller to set up the continuation link.
+     */
+    bool
+    await_ready() const noexcept
+    {
+        return false;
+    }
+
+    /**
+     * Stores the caller's handle as our continuation, then returns
+     * our handle for symmetric transfer (caller suspends, we resume).
+     *
+     * @param caller Handle of the coroutine doing co_await on us
+     *
+     * @return Our handle for symmetric transfer
+     */
+    std::coroutine_handle<>
+    await_suspend(std::coroutine_handle<> caller) noexcept
+    {
+        handle_.promise().continuation_ = caller;
+        return handle_;  // Symmetric transfer
+    }
+
+    /**
+     * Called when the caller resumes after co_await. Rethrows any
+     * exception captured by unhandled_exception().
+     */
+    void
+    await_resume()
+    {
+        if (auto& ep = handle_.promise().exception_)
+            std::rethrow_exception(ep);
+    }
+
+private:
+    // Exclusively-owned coroutine handle. Null after move or default
+    // construction. Destroyed in the destructor.
+    Handle handle_;
+};
+
+/**
+ * CoroTask<T> -- coroutine return type for value-returning coroutines.
+ *
+ * Class / Dependency Diagram
+ * ==========================
+ *
+ *   CoroTask<T>
+ *   +-----------------------------------------------+
+ *   | - handle_ : Handle (coroutine_handle<promise>) |
+ *   +-----------------------------------------------+
+ *   | + handle(), done()                             |
+ *   | + await_ready/suspend/resume  (Awaiter iface)  |
+ *   +-----------------------------------------------+
+ *            |  owns
+ *            v
+ *   promise_type
+ *   +-----------------------------------------------+
+ *   | - result_       : variant<monostate, T,        |
+ *   |                           exception_ptr>       |
+ *   | - continuation_ : std::coroutine_handle<>      |
+ *   +-----------------------------------------------+
+ *   | + get_return_object() -> CoroTask              |
+ *   | + initial_suspend()   -> suspend_always (lazy) |
+ *   | + final_suspend()     -> FinalAwaiter          |
+ *   | + return_value(T)     -> stores in result_[1]  |
+ *   | + unhandled_exception -> stores in result_[2]  |
+ *   +-----------------------------------------------+
+ *            |  returns at final_suspend
+ *            v
+ *   FinalAwaiter  (same symmetric-transfer pattern as CoroTask<void>)
+ *
+ * Value Extraction
+ * ----------------
+ * await_resume() inspects the variant:
+ *   - index 2 (exception_ptr) -> rethrow
+ *   - index 1 (T)             -> return value via move
+ *
+ * Usage Examples
+ * ==============
+ *
+ * 1. Simple value return:
+ *
+ *      CoroTask<int> computeAnswer() { co_return 42; }
+ *
+ *      CoroTask<void> caller() {
+ *          int v = co_await computeAnswer();  // v == 42
+ *      }
+ *
+ * 2. Chaining value-returning coroutines:
+ *
+ *      CoroTask<int> add(int a, int b) { co_return a + b; }
+ *      CoroTask<int> doubleSum(int a, int b) {
+ *          int s = co_await add(a, b);
+ *          co_return s * 2;
+ *      }
+ *
+ * 3. Exception propagation from inner to outer:
+ *
+ *      CoroTask<int> failing() {
+ *          throw std::runtime_error("bad");
+ *          co_return 0;  // never reached
+ *      }
+ *      CoroTask<void> caller() {
+ *          try {
+ *              int v = co_await failing();  // throws here
+ *          } catch (std::runtime_error const& e) {
+ *              // e.what() == "bad"
+ *          }
+ *      }
+ *
+ * Caveats / Pitfalls (in addition to CoroTask<void> caveats above)
+ * ================================================================
+ *
+ * BUG-RISK: await_resume() moves the value out of the variant.
+ *   Calling co_await on the same CoroTask<T> instance twice is undefined
+ *   behavior -- the second call will see a moved-from T. CoroTask is
+ *   single-shot: one co_return, one co_await.
+ *
+ * BUG-RISK: T must be move-constructible.
+ *   return_value(T) takes by value and moves into the variant.
+ *   Types that are not movable cannot be used as T.
+ *
+ * LIMITATION: No co_yield support.
+ *   CoroTask<T> only supports a single co_return. It does not implement
+ *   yield_value(), so using co_yield inside a CoroTask<T> coroutine is a
+ *   compile error. For streaming values, a different return type
+ *   (e.g. Generator<T>) would be needed.
+ *
+ * LIMITATION: Result is only accessible via co_await.
+ *   There is no .get() or .result() method. The value can only be
+ *   extracted by co_await-ing the CoroTask<T> from inside another
+ *   coroutine. For extracting results in non-coroutine code, pass a
+ *   pointer to the caller and write through it (as the tests do).
+ */
+template <typename T>
+class CoroTask
+{
+public:
+    struct promise_type;
+    using Handle = std::coroutine_handle<promise_type>;
+
+    /**
+     * Coroutine promise for value-returning coroutines.
+     * Stores the result as a variant: monostate (not yet set),
+     * T (co_return value), or exception_ptr (unhandled exception).
+     */
+    struct promise_type
+    {
+        // Tri-state result:
+        //   index 0 (monostate) -- coroutine has not yet completed
+        //   index 1 (T)         -- co_return value stored here
+        //   index 2 (exception) -- unhandled exception captured here
+        std::variant<std::monostate, T, std::exception_ptr> result_;
+
+        // Handle to the coroutine co_await-ing this task. Used by
+        // FinalAwaiter for symmetric transfer. Null for top-level tasks.
+        std::coroutine_handle<> continuation_;
+
+        /**
+         * Create the CoroTask return object.
+         * Called by the compiler at coroutine creation.
+         */
+        CoroTask
+        get_return_object()
+        {
+            return CoroTask{Handle::from_promise(*this)};
+        }
+
+        /**
+         * Lazy start. Coroutine body does not run until explicitly resumed.
+         */
+        std::suspend_always
+        initial_suspend() noexcept
+        {
+            return {};
+        }
+
+        /**
+         * Symmetric-transfer awaiter at coroutine completion.
+         * Same pattern as CoroTask<void>::FinalAwaiter.
+         */
+        struct FinalAwaiter
+        {
+            bool
+            await_ready() noexcept
+            {
+                return false;
+            }
+
+            /**
+             * Returns continuation for symmetric transfer, or
+             * noop_coroutine if this is a top-level task.
+             *
+             * @param h Handle to this completing coroutine
+             *
+             * @return Continuation handle, or noop_coroutine
+             */
+            std::coroutine_handle<>
+            await_suspend(Handle h) noexcept
+            {
+                if (auto cont = h.promise().continuation_)
+                    return cont;
+                return std::noop_coroutine();
+            }
+
+            void
+            await_resume() noexcept
+            {
+            }
+        };
+
+        FinalAwaiter
+        final_suspend() noexcept
+        {
+            return {};
+        }
+
+        /**
+         * Called by the compiler for `co_return value;`.
+         * Moves the value into result_ at index 1.
+         *
+         * @param value The value to store
+         */
+        void
+        return_value(T value)
+        {
+            result_.template emplace<1>(std::move(value));
+        }
+
+        /**
+         * Captures unhandled exceptions at index 2 of result_.
+         * Rethrown later in await_resume().
+         */
+        void
+        unhandled_exception()
+        {
+            result_.template emplace<2>(std::current_exception());
+        }
+    };
+
+    /**
+     * Default constructor. Creates an empty (null handle) task.
+     */
+    CoroTask() = default;
+
+    /**
+     * Takes ownership of a compiler-generated coroutine handle.
+     *
+     * @param h Coroutine handle to own
+     */
+    explicit CoroTask(Handle h) : handle_(h)
+    {
+    }
+
+    /**
+     * Destroys the coroutine frame if this task owns one.
+     */
+    ~CoroTask()
+    {
+        if (handle_)
+            handle_.destroy();
+    }
+
+    /**
+     * Move constructor. Transfers handle ownership, leaves other empty.
+     */
+    CoroTask(CoroTask&& other) noexcept : handle_(std::exchange(other.handle_, {}))
+    {
+    }
+
+    /**
+     * Move assignment. Destroys current frame (if any), takes other's.
+     */
+    CoroTask&
+    operator=(CoroTask&& other) noexcept
+    {
+        if (this != &other)
+        {
+            if (handle_)
+                handle_.destroy();
+            handle_ = std::exchange(other.handle_, {});
+        }
+        return *this;
+    }
+
+    CoroTask(CoroTask const&) = delete;
+    CoroTask&
+    operator=(CoroTask const&) = delete;
+
+    /**
+     * @return The underlying coroutine_handle
+     */
+    Handle
+    handle() const
+    {
+        return handle_;
+    }
+
+    /**
+     * @return true if the coroutine has run to completion (or thrown)
+     */
+    bool
+    done() const
+    {
+        return handle_ && handle_.done();
+    }
+
+    // -- Awaiter interface: allows `T val = co_await someCoroTask;` --
+
+    /**
+     * Always false. co_await always suspends to set up continuation.
+     */
+    bool
+    await_ready() const noexcept
+    {
+        return false;
+    }
+
+    /**
+     * Stores caller as continuation, returns our handle for
+     * symmetric transfer.
+     *
+     * @param caller Handle of the coroutine doing co_await on us
+     *
+     * @return Our handle for symmetric transfer
+     */
+    std::coroutine_handle<>
+    await_suspend(std::coroutine_handle<> caller) noexcept
+    {
+        handle_.promise().continuation_ = caller;
+        return handle_;
+    }
+
+    /**
+     * Extracts the result: rethrows if exception, otherwise moves
+     * the T value out of the variant. Single-shot: calling twice
+     * on the same task is undefined (moved-from T).
+     *
+     * @return The co_return-ed value
+     */
+    T
+    await_resume()
+    {
+        auto& result = handle_.promise().result_;
+        if (auto* ep = std::get_if<2>(&result))
+            std::rethrow_exception(*ep);
+        return std::get<1>(std::move(result));
+    }
+
+private:
+    // Exclusively-owned coroutine handle. Null after move or default
+    // construction. Destroyed in the destructor.
+    Handle handle_;
+};
+
+}  // namespace xrpl

include/xrpl/core/CoroTaskRunner.ipp

@@ -0,0 +1,318 @@
+#pragma once
+
+/**
+ * @file CoroTaskRunner.ipp
+ *
+ * CoroTaskRunner inline implementation.
+ *
+ * This file contains the business logic for managing C++20 coroutines
+ * on the JobQueue. It is included at the bottom of JobQueue.h.
+ *
+ * Data Flow: suspend / post / resume cycle
+ * =========================================
+ *
+ *         coroutine body                 CoroTaskRunner              JobQueue
+ *         --------------                 --------------              --------
+ *              |
+ *    co_await runner->suspend()
+ *              |
+ *              +--- await_suspend ------> onSuspend()
+ *              |                            ++nSuspend_ ------------> nSuspend_
+ *              |                          [coroutine is now suspended]
+ *              |
+ *              .    (externally or by JobQueueAwaiter)
+ *              .
+ *              +--- (caller calls) -----> post()
+ *              |                            running_ = true
+ *              |                            addJob(resume) ----------> job enqueued
+ *              |                                                        |
+ *              |                                                      [worker picks up]
+ *              |                                                        |
+ *              +--- <----- resume() <-----------------------------------+
+ *              |             --nSuspend_ ------> nSuspend_
+ *              |             swap in LocalValues (lvs_)
+ *              |             task_.handle().resume()
+ *              |                |
+ *              |    [coroutine body continues here]
+ *              |                |
+ *              |             swap out LocalValues
+ *              |             running_ = false
+ *              |             cv_.notify_all()
+ *              v
+ *
+ * Thread Safety
+ * =============
+ * - mutex_     : guards task_.handle().resume() so that post()-before-suspend
+ *                races cannot resume the coroutine while it is still running.
+ *                (See the race condition discussion in JobQueue.h)
+ * - mutex_run_ : guards running_ flag; used by join() to wait for completion.
+ * - jq_.m_mutex: guards nSuspend_ increments/decrements.
+ *
+ * Common Mistakes When Modifying This File
+ * =========================================
+ *
+ * 1. Changing lock ordering.
+ *    resume() acquires locks in this order: mutex_run_ -> jq_.m_mutex -> mutex_.
+ *    Acquiring them in a different order WILL deadlock. Any new code path
+ *    that touches these mutexes must follow the same order.
+ *
+ * 2. Removing the shared_from_this() capture in post().
+ *    The lambda passed to addJob captures [this, sp = shared_from_this()].
+ *    If you remove sp, 'this' can be destroyed before the job runs,
+ *    causing use-after-free. The sp capture is load-bearing.
+ *
+ * 3. Forgetting to decrement nSuspend_ on a new code path.
+ *    Every ++nSuspend_ must have a matching --nSuspend_. If you add a new
+ *    suspension path (e.g. a new awaiter) and forget to decrement on resume
+ *    or on failure, JobQueue::stop() will hang.
+ *
+ * 4. Calling task_.handle().resume() without holding mutex_.
+ *    This allows a race where the coroutine runs on two threads
+ *    simultaneously. Always hold mutex_ around resume().
+ *
+ * 5. Swapping LocalValues outside of the mutex_ critical section.
+ *    The swap-in and swap-out of LocalValues must bracket the resume()
+ *    call. If you move the swap-out before the lock_guard(mutex_) is
+ *    released, you break LocalValue isolation for any code that runs
+ *    after the coroutine suspends but before the lock is dropped.
+ */
+//
+
+namespace xrpl {
+
+/**
+ * Construct a CoroTaskRunner. Sets running_ to false; does not
+ * create the coroutine. Call init() afterwards.
+ *
+ * @param jq   The JobQueue this coroutine will run on
+ * @param type Job type for scheduling priority
+ * @param name Human-readable name for logging
+ */
+inline JobQueue::CoroTaskRunner::CoroTaskRunner(
+    create_t,
+    JobQueue& jq,
+    JobType type,
+    std::string const& name)
+    : jq_(jq), type_(type), name_(name), running_(false)
+{
+}
+
+/**
+ * Initialize with a coroutine-returning callable.
+ * Stores the callable on the heap (FuncStore) so it outlives the
+ * coroutine frame. Coroutine frames store a reference to the
+ * callable's implicit object parameter (the lambda). If the callable
+ * is a temporary, that reference dangles after the caller returns.
+ * Keeping the callable alive here ensures the coroutine's captures
+ * remain valid.
+ *
+ * @param f Callable: CoroTask<void>(shared_ptr<CoroTaskRunner>)
+ */
+template <class F>
+void
+JobQueue::CoroTaskRunner::init(F&& f)
+{
+    using Fn = std::decay_t<F>;
+    auto store = std::make_unique<FuncStore<Fn>>(std::forward<F>(f));
+    task_ = store->func(shared_from_this());
+    storedFunc_ = std::move(store);
+}
+
+/**
+ * Destructor. Asserts (debug) that the coroutine has finished
+ * or expectEarlyExit() was called.
+ */
+inline JobQueue::CoroTaskRunner::~CoroTaskRunner()
+{
+#ifndef NDEBUG
+    XRPL_ASSERT(finished_, "xrpl::JobQueue::CoroTaskRunner::~CoroTaskRunner : is finished");
+#endif
+}
+
+/**
+ * Increment the JobQueue's suspended-coroutine count (nSuspend_).
+ */
+inline void
+JobQueue::CoroTaskRunner::onSuspend()
+{
+    std::lock_guard lock(jq_.m_mutex);
+    ++jq_.nSuspend_;
+}
+
+/**
+ * Decrement nSuspend_ without resuming.
+ */
+inline void
+JobQueue::CoroTaskRunner::onUndoSuspend()
+{
+    std::lock_guard lock(jq_.m_mutex);
+    --jq_.nSuspend_;
+}
+
+/**
+ * Return a SuspendAwaiter whose await_suspend() increments nSuspend_
+ * before the coroutine actually suspends. The caller must later call
+ * post() or resume() to continue execution.
+ *
+ * @return Awaiter for use with `co_await runner->suspend()`
+ */
+inline auto
+JobQueue::CoroTaskRunner::suspend()
+{
+    /**
+     * Custom awaiter for suspend(). Always suspends (await_ready
+     * returns false) and increments nSuspend_ in await_suspend().
+     */
+    struct SuspendAwaiter
+    {
+        CoroTaskRunner& runner_;  // The runner that owns this coroutine.
+
+        /**
+         * Always returns false so the coroutine suspends.
+         */
+        bool
+        await_ready() const noexcept
+        {
+            return false;
+        }
+
+        /**
+         * Called when the coroutine suspends. Increments nSuspend_
+         * so the JobQueue knows a coroutine is waiting.
+         */
+        void
+        await_suspend(std::coroutine_handle<>) const
+        {
+            runner_.onSuspend();
+        }
+
+        void
+        await_resume() const noexcept
+        {
+        }
+    };
+    return SuspendAwaiter{*this};
+}
+
+/**
+ * Schedule coroutine resumption as a job on the JobQueue.
+ * A shared_ptr capture (sp) prevents this CoroTaskRunner from being
+ * destroyed while the job is queued but not yet executed.
+ *
+ * @return false if the JobQueue rejected the job (shutting down)
+ */
+inline bool
+JobQueue::CoroTaskRunner::post()
+{
+    {
+        std::lock_guard lk(mutex_run_);
+        running_ = true;
+    }
+
+    // sp prevents 'this' from being destroyed while the job is pending
+    if (jq_.addJob(type_, name_, [this, sp = shared_from_this()]() { resume(); }))
+    {
+        return true;
+    }
+
+    // The coroutine will not run. Clean up running_.
+    std::lock_guard lk(mutex_run_);
+    running_ = false;
+    cv_.notify_all();
+    return false;
+}
+
+/**
+ * Resume the coroutine on the current thread.
+ *
+ * Steps:
+ *   1. Set running_ = true (under mutex_run_)
+ *   2. Decrement nSuspend_ (under jq_.m_mutex)
+ *   3. Swap in this coroutine's LocalValues for thread-local isolation
+ *   4. Resume the coroutine handle (under mutex_)
+ *   5. Swap out LocalValues, restoring the thread's previous state
+ *   6. Set running_ = false and notify join() waiters
+ */
+inline void
+JobQueue::CoroTaskRunner::resume()
+{
+    {
+        std::lock_guard lk(mutex_run_);
+        running_ = true;
+    }
+    {
+        std::lock_guard lock(jq_.m_mutex);
+        --jq_.nSuspend_;
+    }
+    auto saved = detail::getLocalValues().release();
+    detail::getLocalValues().reset(&lvs_);
+    std::lock_guard lock(mutex_);
+    XRPL_ASSERT(!task_.done(), "xrpl::JobQueue::CoroTaskRunner::resume : task is not done");
+    task_.handle().resume();
+    detail::getLocalValues().release();
+    detail::getLocalValues().reset(saved);
+    if (task_.done())
+    {
+#ifndef NDEBUG
+        finished_ = true;
+#endif
+        // Destroy the coroutine frame to break the shared_ptr cycle:
+        // frame -> lambda captures shared_ptr<CoroTaskRunner> -> this.
+        // Also release the heap-stored callable (no longer needed).
+        task_ = {};
+        storedFunc_.reset();
+    }
+    std::lock_guard lk(mutex_run_);
+    running_ = false;
+    cv_.notify_all();
+}
+
+/**
+ * @return true if the coroutine has not yet run to completion
+ */
+inline bool
+JobQueue::CoroTaskRunner::runnable() const
+{
+    // After normal completion, task_ is reset to break the shared_ptr cycle
+    // (handle_ becomes null). A null handle means the coroutine is done.
+    return task_.handle() && !task_.done();
+}
+
+/**
+ * Handle early termination when the coroutine never ran (e.g. JobQueue
+ * is stopping). Decrements nSuspend_ and destroys the coroutine frame
+ * to break the shared_ptr cycle: frame -> lambda -> runner -> frame.
+ */
+inline void
+JobQueue::CoroTaskRunner::expectEarlyExit()
+{
+#ifndef NDEBUG
+    if (!finished_)
+#endif
+    {
+        std::lock_guard lock(jq_.m_mutex);
+        --jq_.nSuspend_;
+#ifndef NDEBUG
+        finished_ = true;
+#endif
+    }
+    // Destroy the coroutine frame to break a potential shared_ptr cycle.
+    // The coroutine is at initial_suspend and never ran user code, so
+    // destroying it is safe. Without this, the frame holds a shared_ptr
+    // back to this CoroTaskRunner, creating an unreachable reference cycle.
+    task_ = {};
+    storedFunc_.reset();
+}
+
+/**
+ * Block until the coroutine finishes its current execution slice.
+ * Uses cv_ + mutex_run_ to wait until running_ == false.
+ */
+inline void
+JobQueue::CoroTaskRunner::join()
+{
+    std::unique_lock<std::mutex> lk(mutex_run_);
+    cv_.wait(lk, [this]() { return running_ == false; });
+}
+
+}  // namespace xrpl

include/xrpl/core/JobQueue.h

@@ -2,6 +2,7 @@
 
 #include <xrpl/basics/LocalValue.h>
 #include <xrpl/core/ClosureCounter.h>
+#include <xrpl/core/CoroTask.h>
 #include <xrpl/core/JobTypeData.h>
 #include <xrpl/core/JobTypes.h>
 #include <xrpl/core/detail/Workers.h>
@@ -9,6 +10,7 @@
 
 #include <boost/coroutine/all.hpp>
 
+#include <coroutine>
 #include <set>
 
 namespace xrpl {
@@ -119,6 +121,386 @@ public:
         join();
     };
 
+    /** C++20 coroutine lifecycle manager. Replaces Coro for new code.
+     *
+     *  Class / Inheritance / Dependency Diagram
+     *  =========================================
+     *
+     *  std::enable_shared_from_this<CoroTaskRunner>
+     *            ^
+     *            | (public inheritance)
+     *            |
+     *  CoroTaskRunner
+     *  +---------------------------------------------------+
+     *  | - lvs_         : detail::LocalValues               |
+     *  | - jq_          : JobQueue&                         |
+     *  | - type_        : JobType                           |
+     *  | - name_        : std::string                       |
+     *  | - running_     : bool                              |
+     *  | - mutex_       : std::mutex      (coroutine guard) |
+     *  | - mutex_run_   : std::mutex      (join guard)      |
+     *  | - cv_          : condition_variable                 |
+     *  | - task_        : CoroTask<void>                    |
+     *  | - storedFunc_  : unique_ptr<FuncBase> (type-erased)|
+     *  +---------------------------------------------------+
+     *  | + init(F&&)         : set up coroutine callable    |
+     *  | + onSuspend()       : ++jq_.nSuspend_              |
+     *  | + onUndoSuspend()   : --jq_.nSuspend_              |
+     *  | + suspend()         : returns SuspendAwaiter       |
+     *  | + post()            : schedule resume on JobQueue  |
+     *  | + resume()          : resume coroutine on caller   |
+     *  | + runnable()        : !task_.done()                |
+     *  | + expectEarlyExit() : teardown for failed post     |
+     *  | + join()            : block until not running       |
+     *  +---------------------------------------------------+
+     *          |                          |
+     *          | owns                     | references
+     *          v                          v
+     *    CoroTask<void>             JobQueue
+     *    (coroutine frame)          (thread pool + nSuspend_)
+     *
+     *    FuncBase / FuncStore<F>    (type-erased heap storage
+     *                                for the coroutine lambda)
+     *
+     *  Coroutine Lifecycle (Control Flow)
+     *  ===================================
+     *
+     *  Caller thread              JobQueue worker thread
+     *  -------------              ----------------------
+     *  postCoroTask(f)
+     *    |
+     *    +-- make_shared<CoroTaskRunner>
+     *    +-- init(f)
+     *    |     +-- store lambda on heap (FuncStore)
+     *    |     +-- task_ = f(shared_from_this())
+     *    |           [coroutine created, suspended at initial_suspend]
+     *    +-- ++nSuspend_  (lazy start counts as suspended)
+     *    +-- post()
+     *    |     +-- addJob(type_, [resume]{})
+     *    |                                    resume()
+     *    |                                      |
+     *    |                                      +-- running_ = true
+     *    |                                      +-- --nSuspend_
+     *    |                                      +-- swap in LocalValues
+     *    |                                      +-- task_.handle().resume()
+     *    |                                      |     [coroutine body runs]
+     *    |                                      |     ...
+     *    |                                      |     co_await suspend()
+     *    |                                      |       +-- ++nSuspend_
+     *    |                                      |       [coroutine suspends]
+     *    |                                      +-- swap out LocalValues
+     *    |                                      +-- running_ = false
+     *    |                                      +-- cv_.notify_all()
+     *    |
+     *  post()  <-- called externally or by JobQueueAwaiter
+     *    +-- addJob(type_, [resume]{})
+     *                                         resume()
+     *                                           |
+     *                                           +-- [coroutine body continues]
+     *                                           +-- co_return
+     *                                           +-- running_ = false
+     *                                           +-- cv_.notify_all()
+     *  join()
+     *    +-- cv_.wait([]{!running_})
+     *    +-- [done]
+     *
+     *  Usage Examples
+     *  ==============
+     *
+     *  1. Fire-and-forget coroutine (most common pattern):
+     *
+     *      jq.postCoroTask(jtCLIENT, "MyWork",
+     *          [](auto runner) -> CoroTask<void> {
+     *              doSomeWork();
+     *              co_await runner->suspend();  // yield to other jobs
+     *              doMoreWork();
+     *              co_return;
+     *          });
+     *
+     *  2. Manually controlling suspend / resume (external trigger):
+     *
+     *      auto runner = jq.postCoroTask(jtCLIENT, "ExtTrigger",
+     *          [&result](auto runner) -> CoroTask<void> {
+     *              startAsyncOperation(callback);
+     *              co_await runner->suspend();
+     *              // callback called runner->post() to get here
+     *              result = collectResult();
+     *              co_return;
+     *          });
+     *      // ... later, from the callback:
+     *      runner->post();   // reschedule the coroutine on the JobQueue
+     *
+     *  3. Using JobQueueAwaiter for automatic suspend + repost:
+     *
+     *      jq.postCoroTask(jtCLIENT, "AutoRepost",
+     *          [](auto runner) -> CoroTask<void> {
+     *              step1();
+     *              co_await JobQueueAwaiter{runner};  // yield + auto-repost
+     *              step2();
+     *              co_await JobQueueAwaiter{runner};
+     *              step3();
+     *              co_return;
+     *          });
+     *
+     *  4. Checking shutdown after co_await (cooperative cancellation):
+     *
+     *      jq.postCoroTask(jtCLIENT, "Cancellable",
+     *          [&jq](auto runner) -> CoroTask<void> {
+     *              while (moreWork()) {
+     *                  co_await JobQueueAwaiter{runner};
+     *                  if (jq.isStopping())
+     *                      co_return;  // bail out cleanly
+     *                  processNextItem();
+     *              }
+     *              co_return;
+     *          });
+     *
+     *  Caveats / Pitfalls
+     *  ==================
+     *
+     *  BUG-RISK: Calling suspend() without a matching post()/resume().
+     *    After co_await runner->suspend(), the coroutine is parked and
+     *    nSuspend_ is incremented.  If nothing ever calls post() or
+     *    resume(), the coroutine is leaked and JobQueue::stop() will
+     *    hang forever waiting for nSuspend_ to reach zero.
+     *
+     *  BUG-RISK: Calling post() on an already-running coroutine.
+     *    post() schedules a resume() job.  If the coroutine has not
+     *    actually suspended yet (no co_await executed), the resume job
+     *    will try to call handle().resume() while the coroutine is still
+     *    running on another thread.  This is UB.  The mutex_ prevents
+     *    data corruption but the logic is wrong — always co_await
+     *    suspend() before calling post().  (The test testIncorrectOrder
+     *    shows this works only because mutex_ serializes the calls.)
+     *
+     *  BUG-RISK: Dropping the shared_ptr<CoroTaskRunner> before join().
+     *    The CoroTaskRunner destructor asserts (!finished_ is false).
+     *    If you let the last shared_ptr die while the coroutine is still
+     *    running or suspended, you get an assertion failure in debug and
+     *    UB in release.  Always call join() or expectEarlyExit() first.
+     *
+     *  BUG-RISK: Lambda captures outliving the coroutine frame.
+     *    The lambda passed to postCoroTask is heap-allocated (FuncStore)
+     *    to prevent dangling.  But objects captured by pointer still need
+     *    their own lifetime management.  If you capture a raw pointer to
+     *    a stack variable, and the stack frame exits before the coroutine
+     *    finishes, the pointer dangles.  Use shared_ptr or ensure the
+     *    pointed-to object outlives the coroutine.
+     *
+     *  BUG-RISK: Forgetting co_return in a void coroutine.
+     *    If the coroutine body falls off the end without co_return,
+     *    the compiler may silently treat it as co_return (per standard),
+     *    but some compilers warn.  Always write explicit co_return.
+     *
+     *  LIMITATION: CoroTaskRunner only supports CoroTask<void>.
+     *    The task_ member is CoroTask<void>.  To return values from
+     *    the top-level coroutine, write through a captured pointer
+     *    (as the tests demonstrate), or co_await inner CoroTask<T>
+     *    coroutines that return values.
+     *
+     *  LIMITATION: One coroutine per CoroTaskRunner.
+     *    init() must be called exactly once.  You cannot reuse a
+     *    CoroTaskRunner to run a second coroutine.  Create a new one
+     *    via postCoroTask() instead.
+     *
+     *  LIMITATION: No timeout on join().
+     *    join() blocks indefinitely.  If the coroutine is suspended
+     *    and never posted, join() will deadlock.  Use timed waits
+     *    on the gate pattern (condition_variable + wait_for) in tests.
+     */
+    class CoroTaskRunner : public std::enable_shared_from_this<CoroTaskRunner>
+    {
+    private:
+        // Per-coroutine thread-local storage. Swapped in before resume()
+        // and swapped out after, so each coroutine sees its own LocalValue
+        // state regardless of which worker thread executes it.
+        detail::LocalValues lvs_;
+
+        // Back-reference to the owning JobQueue. Used to post jobs,
+        // increment/decrement nSuspend_, and acquire jq_.m_mutex.
+        JobQueue& jq_;
+
+        // Job type passed to addJob() when posting this coroutine.
+        JobType type_;
+
+        // Human-readable name for this coroutine job (for logging).
+        std::string name_;
+
+        // True while the coroutine is actively executing on a thread.
+        // Guarded by mutex_run_. join() blocks until this is false.
+        bool running_;
+
+        // Guards task_.handle().resume() to prevent the coroutine from
+        // running on two threads simultaneously. Handles the race where
+        // post() enqueues a resume before the coroutine has actually
+        // suspended (post-before-suspend pattern).
+        std::mutex mutex_;
+
+        // Guards running_ flag. Used with cv_ for join() to wait
+        // until the coroutine finishes its current execution slice.
+        std::mutex mutex_run_;
+
+        // Notified when running_ transitions to false, allowing
+        // join() waiters to wake up.
+        std::condition_variable cv_;
+
+        // The coroutine handle wrapper. Owns the coroutine frame.
+        // Set by init(), reset to empty by expectEarlyExit() on
+        // early termination.
+        CoroTask<void> task_;
+
+        /**
+         * Type-erased base for heap-stored callables.
+         * Prevents the coroutine lambda from being destroyed before
+         * the coroutine frame is done with it.
+         *
+         * @see FuncStore
+         */
+        struct FuncBase
+        {
+            virtual ~FuncBase() = default;
+        };
+
+        /**
+         * Concrete type-erased storage for a callable of type F.
+         * The coroutine frame stores a reference to the lambda's implicit
+         * object parameter. If the lambda is a temporary, that reference
+         * dangles after the call returns. FuncStore keeps it alive on
+         * the heap for the lifetime of the CoroTaskRunner.
+         */
+        template <class F>
+        struct FuncStore : FuncBase
+        {
+            F func;  // The stored callable (coroutine lambda).
+            explicit FuncStore(F&& f) : func(std::move(f))
+            {
+            }
+        };
+
+        // Heap-allocated callable storage. Set by init(), ensures the
+        // lambda outlives the coroutine frame that references it.
+        std::unique_ptr<FuncBase> storedFunc_;
+
+#ifndef NDEBUG
+        // Debug-only flag. True once the coroutine has completed or
+        // expectEarlyExit() was called. Asserted in the destructor
+        // to catch leaked runners.
+        bool finished_ = false;
+#endif
+
+    public:
+        /**
+         * Tag type for private construction. Prevents external code
+         * from constructing CoroTaskRunner directly. Use postCoroTask().
+         */
+        struct create_t
+        {
+            explicit create_t() = default;
+        };
+
+        /**
+         * Construct a CoroTaskRunner. Private by convention (create_t tag).
+         *
+         * @param jq   The JobQueue this coroutine will run on
+         * @param type Job type for scheduling priority
+         * @param name Human-readable name for logging
+         */
+        CoroTaskRunner(create_t, JobQueue&, JobType, std::string const&);
+
+        CoroTaskRunner(CoroTaskRunner const&) = delete;
+        CoroTaskRunner&
+        operator=(CoroTaskRunner const&) = delete;
+
+        /**
+         * Destructor. Asserts (debug) that the coroutine has finished
+         * or expectEarlyExit() was called.
+         */
+        ~CoroTaskRunner();
+
+        /**
+         * Initialize with a coroutine-returning callable.
+         * Must be called exactly once, after the object is managed by
+         * shared_ptr (because init uses shared_from_this internally).
+         * This is handled automatically by postCoroTask().
+         *
+         * @param f Callable: CoroTask<void>(shared_ptr<CoroTaskRunner>)
+         */
+        template <class F>
+        void
+        init(F&& f);
+
+        /**
+         * Increment the JobQueue's suspended-coroutine count (nSuspend_).
+         * Called when the coroutine is about to suspend. Every call
+         * must be balanced by a corresponding decrement (via resume()
+         * or onUndoSuspend()), or JobQueue::stop() will hang.
+         */
+        void
+        onSuspend();
+
+        /**
+         * Decrement nSuspend_ without resuming.
+         * Used to undo onSuspend() when a scheduled post() fails
+         * (e.g. JobQueue is stopping).
+         */
+        void
+        onUndoSuspend();
+
+        /**
+         * Suspend the coroutine.
+         * The awaiter's await_suspend() increments nSuspend_ before the
+         * coroutine actually suspends. The caller must later call post()
+         * or resume() to continue execution.
+         *
+         * @return An awaiter for use with `co_await runner->suspend()`
+         */
+        auto
+        suspend();
+
+        /**
+         * Schedule coroutine resumption as a job on the JobQueue.
+         * Captures shared_from_this() to prevent this runner from being
+         * destroyed while the job is queued.
+         *
+         * @return true if the job was accepted; false if the JobQueue
+         *         is stopping (caller must handle cleanup)
+         */
+        bool
+        post();
+
+        /**
+         * Resume the coroutine on the current thread.
+         * Decrements nSuspend_, swaps in LocalValues, resumes the
+         * coroutine handle, swaps out LocalValues, and notifies join()
+         * waiters. Lock ordering: mutex_run_ -> jq_.m_mutex -> mutex_.
+         */
+        void
+        resume();
+
+        /**
+         * @return true if the coroutine has not yet run to completion
+         */
+        bool
+        runnable() const;
+
+        /**
+         * Handle early termination when the coroutine never ran.
+         * Decrements nSuspend_ and destroys the coroutine frame to
+         * break the shared_ptr cycle (frame -> lambda -> runner -> frame).
+         * Called by postCoroTask() when post() fails.
+         */
+        void
+        expectEarlyExit();
+
+        /**
+         * Block until the coroutine finishes its current execution slice.
+         * Uses cv_ + mutex_run_ to wait until running_ == false.
+         * Warning: deadlocks if the coroutine is suspended and never posted.
+         */
+        void
+        join();
+    };
+
     using JobFunction = std::function<void()>;
 
     JobQueue(
@@ -165,6 +547,19 @@ public:
     std::shared_ptr<Coro>
     postCoro(JobType t, std::string const& name, F&& f);
 
+    /** Creates a C++20 coroutine and adds a job to the queue to run it.
+
+        @param t The type of job.
+        @param name Name of the job.
+        @param f Callable with signature
+            CoroTask<void>(std::shared_ptr<CoroTaskRunner>).
+
+        @return shared_ptr to posted CoroTaskRunner. nullptr if not successful.
+    */
+    template <class F>
+    std::shared_ptr<CoroTaskRunner>
+    postCoroTask(JobType t, std::string const& name, F&& f);
+
     /** Jobs waiting at this priority.
      */
     int
@@ -379,6 +774,7 @@ private:
 }  // namespace xrpl
 
 #include <xrpl/core/Coro.ipp>
+#include <xrpl/core/CoroTaskRunner.ipp>
 
 namespace xrpl {
 
@@ -401,4 +797,54 @@ JobQueue::postCoro(JobType t, std::string const& name, F&& f)
     return coro;
 }
 
+// postCoroTask — entry point for launching a C++20 coroutine on the JobQueue.
+//
+// Control Flow
+// ============
+//
+//   postCoroTask(t, name, f)
+//     |
+//     +-- 1. Create CoroTaskRunner (shared_ptr, ref-counted)
+//     |
+//     +-- 2. runner->init(f)
+//     |        +-- Heap-allocate the lambda (FuncStore) to prevent
+//     |        |   dangling captures in the coroutine frame
+//     |        +-- task_ = f(shared_from_this())
+//     |              [coroutine created but NOT started — lazy initial_suspend]
+//     |
+//     +-- 3. ++nSuspend_   (mirrors Boost Coro ctor's implicit yield)
+//     |        The coroutine is "suspended" from the JobQueue's perspective
+//     |        even though it hasn't run yet — this keeps the JQ shutdown
+//     |        logic correct (it waits for nSuspend_ to reach 0).
+//     |
+//     +-- 4. runner->post()
+//     |        +-- success: job queued, worker will call resume()
+//     |        |            return runner to caller
+//     |        +-- failure: JQ is stopping
+//     |              +-- runner->expectEarlyExit()
+//     |              |     --nSuspend_, destroy coroutine frame
+//     |              +-- return nullptr
+//
+template <class F>
+std::shared_ptr<JobQueue::CoroTaskRunner>
+JobQueue::postCoroTask(JobType t, std::string const& name, F&& f)
+{
+    auto runner = std::make_shared<CoroTaskRunner>(CoroTaskRunner::create_t{}, *this, t, name);
+    runner->init(std::forward<F>(f));
+
+    // Account for the initial suspension (lazy start).
+    // Mirrors the yield() in the Boost Coro constructor.
+    {
+        std::lock_guard lock(m_mutex);
+        ++nSuspend_;
+    }
+
+    if (!runner->post())
+    {
+        runner->expectEarlyExit();
+        runner.reset();
+    }
+    return runner;
+}
+
 }  // namespace xrpl

include/xrpl/core/JobQueueAwaiter.h

@@ -0,0 +1,174 @@
+#pragma once
+
+#include <xrpl/core/JobQueue.h>
+
+#include <coroutine>
+#include <memory>
+
+namespace xrpl {
+
+/**
+ * Awaiter that suspends and immediately reschedules on the JobQueue.
+ * Equivalent to calling yield() followed by post() in the old Coro API.
+ *
+ * Usage:
+ *     co_await JobQueueAwaiter{runner};
+ *
+ * What it waits for: The coroutine is re-queued as a job and resumes
+ * when a worker thread picks it up.
+ *
+ * Which thread resumes: A JobQueue worker thread.
+ *
+ * What await_resume() returns: void.
+ *
+ * Dependency Diagram
+ * ==================
+ *
+ *   JobQueueAwaiter
+ *   +----------------------------------------------+
+ *   | + runner : shared_ptr<CoroTaskRunner>         |
+ *   +----------------------------------------------+
+ *   | + await_ready()   -> false (always suspend)   |
+ *   | + await_suspend() -> bool (suspend or cancel) |
+ *   | + await_resume()  -> void                     |
+ *   +----------------------------------------------+
+ *          |                         |
+ *          | uses                    | uses
+ *          v                         v
+ *   CoroTaskRunner              JobQueue
+ *   .onSuspend()                (via runner->post() -> addJob)
+ *   .onUndoSuspend()
+ *   .post()
+ *
+ * Control Flow (await_suspend)
+ * ============================
+ *
+ *   co_await JobQueueAwaiter{runner}
+ *     |
+ *     +-- await_ready() -> false
+ *     +-- await_suspend(handle)
+ *           |
+ *           +-- runner->onSuspend()     // ++nSuspend_
+ *           +-- runner->post()          // addJob to JobQueue
+ *           |     |
+ *           |     +-- success? return true   // coroutine stays suspended
+ *           |     |                          // worker thread will call resume()
+ *           |     +-- failure? (JQ stopping)
+ *           |           +-- runner->onUndoSuspend()  // --nSuspend_
+ *           |           +-- return false   // coroutine continues immediately
+ *           |                              // so it can clean up and co_return
+ *
+ * Usage Examples
+ * ==============
+ *
+ * 1. Yield and auto-repost (most common -- replaces yield() + post()):
+ *
+ *     CoroTask<void> handler(auto runner) {
+ *         doPartA();
+ *         co_await JobQueueAwaiter{runner};  // yield + repost
+ *         doPartB();                         // runs on a worker thread
+ *         co_return;
+ *     }
+ *
+ * 2. Multiple yield points in a loop:
+ *
+ *     CoroTask<void> batchProcessor(auto runner) {
+ *         for (auto& item : items) {
+ *             process(item);
+ *             co_await JobQueueAwaiter{runner};  // let other jobs run
+ *         }
+ *         co_return;
+ *     }
+ *
+ * 3. Graceful shutdown -- checking after resume:
+ *
+ *     CoroTask<void> longTask(auto runner, JobQueue& jq) {
+ *         while (hasWork()) {
+ *             co_await JobQueueAwaiter{runner};
+ *             // If JQ is stopping, await_suspend returns false and
+ *             // the coroutine continues immediately without re-queuing.
+ *             // Always check isStopping() to decide whether to proceed:
+ *             if (jq.isStopping())
+ *                 co_return;
+ *             doNextChunk();
+ *         }
+ *         co_return;
+ *     }
+ *
+ * Caveats / Pitfalls
+ * ==================
+ *
+ * BUG-RISK: Using a stale or null runner.
+ *   The runner shared_ptr must be valid and point to the CoroTaskRunner
+ *   that owns the coroutine currently executing. Passing a runner from
+ *   a different coroutine, or a default-constructed shared_ptr, is UB.
+ *
+ * BUG-RISK: Assuming resume happens on the same thread.
+ *   After co_await JobQueueAwaiter, the coroutine resumes on whatever
+ *   worker thread picks up the job. Do not rely on thread-local state
+ *   unless it is managed through LocalValue (which CoroTaskRunner
+ *   automatically swaps in/out).
+ *
+ * BUG-RISK: Ignoring the shutdown path.
+ *   When the JobQueue is stopping, post() fails and await_suspend()
+ *   returns false (coroutine does NOT actually suspend). The coroutine
+ *   body continues immediately on the same thread. If your code after
+ *   co_await assumes it was re-queued and is running on a worker thread,
+ *   that assumption breaks during shutdown. Always handle the "JQ is
+ *   stopping" case, either by checking jq.isStopping() or by letting
+ *   the coroutine fall through to co_return naturally.
+ *
+ * DIFFERENCE from runner->suspend() + runner->post():
+ *   JobQueueAwaiter combines both in one atomic operation. With the
+ *   manual suspend()/post() pattern, there is a window between the
+ *   two calls where an external event could race. JobQueueAwaiter
+ *   removes that window -- onSuspend() and post() happen within the
+ *   same await_suspend() call while the coroutine is guaranteed to
+ *   be suspended. Prefer JobQueueAwaiter unless you need an external
+ *   party to decide *when* to call post().
+ */
+struct JobQueueAwaiter
+{
+    // The CoroTaskRunner that owns the currently executing coroutine.
+    std::shared_ptr<JobQueue::CoroTaskRunner> runner;
+
+    /**
+     * Always returns false so the coroutine suspends.
+     */
+    bool
+    await_ready() const noexcept
+    {
+        return false;
+    }
+
+    /**
+     * Increment nSuspend (equivalent to yield()) and schedule resume
+     * on the JobQueue (equivalent to post()). If the JobQueue is
+     * stopping, undoes the suspend count and returns false so the
+     * coroutine continues immediately and can clean up.
+     *
+     * @return true if coroutine should stay suspended (job posted);
+     *         false if coroutine should continue (JQ stopping)
+     */
+    bool
+    await_suspend(std::coroutine_handle<>)
+    {
+        runner->onSuspend();
+        if (!runner->post())
+        {
+            // JobQueue is stopping. Undo the suspend count and
+            // don't actually suspend — the coroutine continues
+            // immediately so it can clean up and co_return.
+            runner->onUndoSuspend();
+            return false;
+        }
+        return true;
+    }
+
+    void
+    await_resume() const noexcept
+    {
+    }
+};
+
+}  // namespace xrpl

src/test/app/Path_test.cpp

@@ -8,6 +8,7 @@
 #include <xrpld/rpc/detail/Tuning.h>
 
 #include <xrpl/beast/unit_test.h>
+#include <xrpl/core/CoroTask.h>
 #include <xrpl/core/JobQueue.h>
 #include <xrpl/json/json_reader.h>
 #include <xrpl/protocol/ApiVersion.h>
@@ -131,7 +132,6 @@ public:
              c,
              Role::USER,
              {},
-             {},
              RPC::apiVersionIfUnspecified},
             {},
             {}};
@@ -155,11 +155,11 @@ public:
 
         Json::Value result;
         gate g;
-        app.getJobQueue().postCoro(jtCLIENT, "RPC-Client", [&](auto const& coro) {
+        app.getJobQueue().postCoroTask(jtCLIENT, "RPC-Client", [&](auto) -> CoroTask<void> {
             context.params = std::move(params);
-            context.coro = coro;
             RPC::doCommand(context, result);
             g.signal();
+            co_return;
         });
 
         using namespace std::chrono_literals;
@@ -240,28 +240,27 @@ public:
              c,
              Role::USER,
              {},
-             {},
              RPC::apiVersionIfUnspecified},
             {},
             {}};
         Json::Value result;
         gate g;
         // Test RPC::Tuning::max_src_cur source currencies.
-        app.getJobQueue().postCoro(jtCLIENT, "RPC-Client", [&](auto const& coro) {
+        app.getJobQueue().postCoroTask(jtCLIENT, "RPC-Client", [&](auto) -> CoroTask<void> {
             context.params = rpf(Account("alice"), Account("bob"), RPC::Tuning::max_src_cur);
-            context.coro = coro;
             RPC::doCommand(context, result);
             g.signal();
+            co_return;
         });
         BEAST_EXPECT(g.wait_for(5s));
         BEAST_EXPECT(!result.isMember(jss::error));
 
         // Test more than RPC::Tuning::max_src_cur source currencies.
-        app.getJobQueue().postCoro(jtCLIENT, "RPC-Client", [&](auto const& coro) {
+        app.getJobQueue().postCoroTask(jtCLIENT, "RPC-Client", [&](auto) -> CoroTask<void> {
             context.params = rpf(Account("alice"), Account("bob"), RPC::Tuning::max_src_cur + 1);
-            context.coro = coro;
             RPC::doCommand(context, result);
             g.signal();
+            co_return;
         });
         BEAST_EXPECT(g.wait_for(5s));
         BEAST_EXPECT(result.isMember(jss::error));
@@ -269,22 +268,22 @@ public:
         // Test RPC::Tuning::max_auto_src_cur source currencies.
         for (auto i = 0; i < (RPC::Tuning::max_auto_src_cur - 1); ++i)
             env.trust(Account("alice")[std::to_string(i + 100)](100), "bob");
-        app.getJobQueue().postCoro(jtCLIENT, "RPC-Client", [&](auto const& coro) {
+        app.getJobQueue().postCoroTask(jtCLIENT, "RPC-Client", [&](auto) -> CoroTask<void> {
             context.params = rpf(Account("alice"), Account("bob"), 0);
-            context.coro = coro;
             RPC::doCommand(context, result);
             g.signal();
+            co_return;
         });
         BEAST_EXPECT(g.wait_for(5s));
         BEAST_EXPECT(!result.isMember(jss::error));
 
         // Test more than RPC::Tuning::max_auto_src_cur source currencies.
         env.trust(Account("alice")["AUD"](100), "bob");
-        app.getJobQueue().postCoro(jtCLIENT, "RPC-Client", [&](auto const& coro) {
+        app.getJobQueue().postCoroTask(jtCLIENT, "RPC-Client", [&](auto) -> CoroTask<void> {
             context.params = rpf(Account("alice"), Account("bob"), 0);
-            context.coro = coro;
             RPC::doCommand(context, result);
             g.signal();
+            co_return;
         });
         BEAST_EXPECT(g.wait_for(5s));
         BEAST_EXPECT(result.isMember(jss::error));

src/test/core/CoroTask_test.cpp

@@ -0,0 +1,537 @@
+#include <test/jtx.h>
+
+#include <xrpl/core/JobQueue.h>
+#include <xrpl/core/JobQueueAwaiter.h>
+
+#include <chrono>
+#include <mutex>
+
+namespace xrpl {
+namespace test {
+
+/**
+ * Test suite for the C++20 coroutine primitives: CoroTask, CoroTaskRunner,
+ * and JobQueueAwaiter.
+ *
+ * Dependency Diagram
+ * ==================
+ *
+ *   CoroTask_test
+ *   +-------------------------------------------------+
+ *   | + gate (inner class) : condition_variable helper |
+ *   +-------------------------------------------------+
+ *          |  uses
+ *          v
+ *   jtx::Env  -->  JobQueue::postCoroTask()
+ *                       |
+ *                       +-- CoroTaskRunner (suspend / post / resume)
+ *                       +-- CoroTask<void> / CoroTask<T>
+ *                       +-- JobQueueAwaiter
+ *
+ * Test Coverage Matrix
+ * ====================
+ *
+ *   Test                      | Primitives exercised
+ *   --------------------------+----------------------------------------------
+ *   testVoidCompletion        | CoroTask<void> basic lifecycle
+ *   testCorrectOrder          | suspend() -> join() -> post() -> complete
+ *   testIncorrectOrder        | post() before suspend() (race-safe path)
+ *   testJobQueueAwaiter       | JobQueueAwaiter suspend + auto-repost
+ *   testThreadSpecificStorage | LocalValue isolation across coroutines
+ *   testExceptionPropagation  | unhandled_exception() in promise_type
+ *   testMultipleYields        | N sequential suspend/resume cycles
+ *   testValueReturn           | CoroTask<T> co_return value
+ *   testValueException        | CoroTask<T> exception via co_await
+ *   testValueChaining         | nested CoroTask<T> -> CoroTask<T>
+ *   testShutdownRejection     | postCoroTask returns nullptr when stopping
+ */
+class CoroTask_test : public beast::unit_test::suite
+{
+public:
+    /**
+     * Simple one-shot gate for synchronizing between test thread
+     * and coroutine worker threads. signal() sets the flag;
+     * wait_for() blocks until signaled or timeout.
+     */
+    class gate
+    {
+    private:
+        std::condition_variable cv_;
+        std::mutex mutex_;
+        bool signaled_ = false;
+
+    public:
+        /**
+         * Block until signaled or timeout expires.
+         *
+         * @param rel_time Maximum duration to wait
+         *
+         * @return true if signaled before timeout
+         */
+        template <class Rep, class Period>
+        bool
+        wait_for(std::chrono::duration<Rep, Period> const& rel_time)
+        {
+            std::unique_lock<std::mutex> lk(mutex_);
+            auto b = cv_.wait_for(lk, rel_time, [this] { return signaled_; });
+            signaled_ = false;
+            return b;
+        }
+
+        /**
+         * Signal the gate, waking any waiting thread.
+         */
+        void
+        signal()
+        {
+            std::lock_guard lk(mutex_);
+            signaled_ = true;
+            cv_.notify_all();
+        }
+    };
+
+    // NOTE: All coroutine lambdas passed to postCoroTask use explicit
+    // pointer-by-value captures instead of [&] to work around a GCC 14
+    // bug where reference captures in coroutine lambdas are corrupted
+    // in the coroutine frame.
+
+    /**
+     * CoroTask<void> runs to completion and runner becomes non-runnable.
+     */
+    void
+    testVoidCompletion()
+    {
+        using namespace std::chrono_literals;
+        using namespace jtx;
+
+        testcase("void completion");
+
+        Env env(*this, envconfig([](std::unique_ptr<Config> cfg) {
+            cfg->FORCE_MULTI_THREAD = true;
+            return cfg;
+        }));
+
+        gate g;
+        auto runner = env.app().getJobQueue().postCoroTask(
+            jtCLIENT, "CoroTaskTest", [gp = &g](auto) -> CoroTask<void> {
+                gp->signal();
+                co_return;
+            });
+        BEAST_EXPECT(runner);
+        BEAST_EXPECT(g.wait_for(5s));
+        runner->join();
+        BEAST_EXPECT(!runner->runnable());
+    }
+
+    /**
+     * Correct order: suspend, join, post, complete.
+     * Mirrors existing Coroutine_test::correct_order.
+     */
+    void
+    testCorrectOrder()
+    {
+        using namespace std::chrono_literals;
+        using namespace jtx;
+
+        testcase("correct order");
+
+        Env env(*this, envconfig([](std::unique_ptr<Config> cfg) {
+            cfg->FORCE_MULTI_THREAD = true;
+            return cfg;
+        }));
+
+        gate g1, g2;
+        std::shared_ptr<JobQueue::CoroTaskRunner> r;
+        auto runner = env.app().getJobQueue().postCoroTask(
+            jtCLIENT,
+            "CoroTaskTest",
+            [rp = &r, g1p = &g1, g2p = &g2](auto runner) -> CoroTask<void> {
+                *rp = runner;
+                g1p->signal();
+                co_await runner->suspend();
+                g2p->signal();
+                co_return;
+            });
+        BEAST_EXPECT(runner);
+        BEAST_EXPECT(g1.wait_for(5s));
+        runner->join();
+        runner->post();
+        BEAST_EXPECT(g2.wait_for(5s));
+        runner->join();
+    }
+
+    /**
+     * Incorrect order: post() before suspend(). Verifies the
+     * race-safe path. Mirrors Coroutine_test::incorrect_order.
+     */
+    void
+    testIncorrectOrder()
+    {
+        using namespace std::chrono_literals;
+        using namespace jtx;
+
+        testcase("incorrect order");
+
+        Env env(*this, envconfig([](std::unique_ptr<Config> cfg) {
+            cfg->FORCE_MULTI_THREAD = true;
+            return cfg;
+        }));
+
+        gate g;
+        env.app().getJobQueue().postCoroTask(
+            jtCLIENT, "CoroTaskTest", [gp = &g](auto runner) -> CoroTask<void> {
+                runner->post();
+                co_await runner->suspend();
+                gp->signal();
+                co_return;
+            });
+        BEAST_EXPECT(g.wait_for(5s));
+    }
+
+    /**
+     * JobQueueAwaiter suspend + auto-repost across multiple yield points.
+     */
+    void
+    testJobQueueAwaiter()
+    {
+        using namespace std::chrono_literals;
+        using namespace jtx;
+
+        testcase("JobQueueAwaiter");
+
+        Env env(*this, envconfig([](std::unique_ptr<Config> cfg) {
+            cfg->FORCE_MULTI_THREAD = true;
+            return cfg;
+        }));
+
+        gate g;
+        int step = 0;
+        env.app().getJobQueue().postCoroTask(
+            jtCLIENT, "CoroTaskTest", [sp = &step, gp = &g](auto runner) -> CoroTask<void> {
+                *sp = 1;
+                co_await JobQueueAwaiter{runner};
+                *sp = 2;
+                co_await JobQueueAwaiter{runner};
+                *sp = 3;
+                gp->signal();
+                co_return;
+            });
+        BEAST_EXPECT(g.wait_for(5s));
+        BEAST_EXPECT(step == 3);
+    }
+
+    /**
+     * Per-coroutine LocalValue isolation. Each coroutine sees its own
+     * copy of thread-local state. Mirrors Coroutine_test::thread_specific_storage.
+     */
+    void
+    testThreadSpecificStorage()
+    {
+        using namespace std::chrono_literals;
+        using namespace jtx;
+
+        testcase("thread specific storage");
+        Env env(*this);
+
+        auto& jq = env.app().getJobQueue();
+
+        static int const N = 4;
+        std::array<std::shared_ptr<JobQueue::CoroTaskRunner>, N> a;
+
+        LocalValue<int> lv(-1);
+        BEAST_EXPECT(*lv == -1);
+
+        gate g;
+        jq.addJob(jtCLIENT, "LocalValTest", [&]() {
+            this->BEAST_EXPECT(*lv == -1);
+            *lv = -2;
+            this->BEAST_EXPECT(*lv == -2);
+            g.signal();
+        });
+        BEAST_EXPECT(g.wait_for(5s));
+        BEAST_EXPECT(*lv == -1);
+
+        for (int i = 0; i < N; ++i)
+        {
+            jq.postCoroTask(
+                jtCLIENT,
+                "CoroTaskTest",
+                [this, ap = &a, gp = &g, lvp = &lv, id = i](auto runner) -> CoroTask<void> {
+                    (*ap)[id] = runner;
+                    gp->signal();
+                    co_await runner->suspend();
+
+                    this->BEAST_EXPECT(**lvp == -1);
+                    **lvp = id;
+                    this->BEAST_EXPECT(**lvp == id);
+                    gp->signal();
+                    co_await runner->suspend();
+
+                    this->BEAST_EXPECT(**lvp == id);
+                    co_return;
+                });
+            BEAST_EXPECT(g.wait_for(5s));
+            a[i]->join();
+        }
+        for (auto const& r : a)
+        {
+            r->post();
+            BEAST_EXPECT(g.wait_for(5s));
+            r->join();
+        }
+        for (auto const& r : a)
+        {
+            r->post();
+            r->join();
+        }
+
+        jq.addJob(jtCLIENT, "LocalValTest", [&]() {
+            this->BEAST_EXPECT(*lv == -2);
+            g.signal();
+        });
+        BEAST_EXPECT(g.wait_for(5s));
+        BEAST_EXPECT(*lv == -1);
+    }
+
+    /**
+     * Exception thrown in coroutine body is caught by
+     * promise_type::unhandled_exception(). Coroutine completes.
+     */
+    void
+    testExceptionPropagation()
+    {
+        using namespace std::chrono_literals;
+        using namespace jtx;
+
+        testcase("exception propagation");
+
+        Env env(*this, envconfig([](std::unique_ptr<Config> cfg) {
+            cfg->FORCE_MULTI_THREAD = true;
+            return cfg;
+        }));
+
+        gate g;
+        auto runner = env.app().getJobQueue().postCoroTask(
+            jtCLIENT, "CoroTaskTest", [gp = &g](auto) -> CoroTask<void> {
+                gp->signal();
+                throw std::runtime_error("test exception");
+                co_return;
+            });
+        BEAST_EXPECT(runner);
+        BEAST_EXPECT(g.wait_for(5s));
+        runner->join();
+        // The exception is caught by promise_type::unhandled_exception()
+        // and the coroutine is considered done
+        BEAST_EXPECT(!runner->runnable());
+    }
+
+    /**
+     * Multiple sequential suspend/resume cycles via co_await.
+     */
+    void
+    testMultipleYields()
+    {
+        using namespace std::chrono_literals;
+        using namespace jtx;
+
+        testcase("multiple yields");
+
+        Env env(*this, envconfig([](std::unique_ptr<Config> cfg) {
+            cfg->FORCE_MULTI_THREAD = true;
+            return cfg;
+        }));
+
+        gate g;
+        int counter = 0;
+        std::shared_ptr<JobQueue::CoroTaskRunner> r;
+        auto runner = env.app().getJobQueue().postCoroTask(
+            jtCLIENT,
+            "CoroTaskTest",
+            [rp = &r, cp = &counter, gp = &g](auto runner) -> CoroTask<void> {
+                *rp = runner;
+                ++(*cp);
+                gp->signal();
+                co_await runner->suspend();
+                ++(*cp);
+                gp->signal();
+                co_await runner->suspend();
+                ++(*cp);
+                gp->signal();
+                co_return;
+            });
+        BEAST_EXPECT(runner);
+
+        BEAST_EXPECT(g.wait_for(5s));
+        BEAST_EXPECT(counter == 1);
+        runner->join();
+
+        runner->post();
+        BEAST_EXPECT(g.wait_for(5s));
+        BEAST_EXPECT(counter == 2);
+        runner->join();
+
+        runner->post();
+        BEAST_EXPECT(g.wait_for(5s));
+        BEAST_EXPECT(counter == 3);
+        runner->join();
+        BEAST_EXPECT(!runner->runnable());
+    }
+
+    /**
+     * CoroTask<T> returns a value via co_return. Outer coroutine
+     * extracts it with co_await.
+     */
+    void
+    testValueReturn()
+    {
+        using namespace std::chrono_literals;
+        using namespace jtx;
+
+        testcase("value return");
+
+        Env env(*this, envconfig([](std::unique_ptr<Config> cfg) {
+            cfg->FORCE_MULTI_THREAD = true;
+            return cfg;
+        }));
+
+        gate g;
+        int result = 0;
+        auto runner = env.app().getJobQueue().postCoroTask(
+            jtCLIENT, "CoroTaskTest", [rp = &result, gp = &g](auto) -> CoroTask<void> {
+                auto inner = []() -> CoroTask<int> { co_return 42; };
+                *rp = co_await inner();
+                gp->signal();
+                co_return;
+            });
+        BEAST_EXPECT(runner);
+        BEAST_EXPECT(g.wait_for(5s));
+        runner->join();
+        BEAST_EXPECT(result == 42);
+        BEAST_EXPECT(!runner->runnable());
+    }
+
+    /**
+     * CoroTask<T> propagates exceptions from inner coroutines.
+     * Outer coroutine catches via try/catch around co_await.
+     */
+    void
+    testValueException()
+    {
+        using namespace std::chrono_literals;
+        using namespace jtx;
+
+        testcase("value exception");
+
+        Env env(*this, envconfig([](std::unique_ptr<Config> cfg) {
+            cfg->FORCE_MULTI_THREAD = true;
+            return cfg;
+        }));
+
+        gate g;
+        bool caught = false;
+        auto runner = env.app().getJobQueue().postCoroTask(
+            jtCLIENT, "CoroTaskTest", [cp = &caught, gp = &g](auto) -> CoroTask<void> {
+                auto inner = []() -> CoroTask<int> {
+                    throw std::runtime_error("inner error");
+                    co_return 0;
+                };
+                try
+                {
+                    co_await inner();
+                }
+                catch (std::runtime_error const& e)
+                {
+                    *cp = true;
+                }
+                gp->signal();
+                co_return;
+            });
+        BEAST_EXPECT(runner);
+        BEAST_EXPECT(g.wait_for(5s));
+        runner->join();
+        BEAST_EXPECT(caught);
+        BEAST_EXPECT(!runner->runnable());
+    }
+
+    /**
+     * CoroTask<T> chaining. Nested value-returning coroutines
+     * compose via co_await.
+     */
+    void
+    testValueChaining()
+    {
+        using namespace std::chrono_literals;
+        using namespace jtx;
+
+        testcase("value chaining");
+
+        Env env(*this, envconfig([](std::unique_ptr<Config> cfg) {
+            cfg->FORCE_MULTI_THREAD = true;
+            return cfg;
+        }));
+
+        gate g;
+        int result = 0;
+        auto runner = env.app().getJobQueue().postCoroTask(
+            jtCLIENT, "CoroTaskTest", [rp = &result, gp = &g](auto) -> CoroTask<void> {
+                auto add = [](int a, int b) -> CoroTask<int> { co_return a + b; };
+                auto mul = [add](int a, int b) -> CoroTask<int> {
+                    int sum = co_await add(a, b);
+                    co_return sum * 2;
+                };
+                *rp = co_await mul(3, 4);
+                gp->signal();
+                co_return;
+            });
+        BEAST_EXPECT(runner);
+        BEAST_EXPECT(g.wait_for(5s));
+        runner->join();
+        BEAST_EXPECT(result == 14);  // (3 + 4) * 2
+        BEAST_EXPECT(!runner->runnable());
+    }
+
+    /**
+     * postCoroTask returns nullptr when JobQueue is stopping.
+     */
+    void
+    testShutdownRejection()
+    {
+        using namespace std::chrono_literals;
+        using namespace jtx;
+
+        testcase("shutdown rejection");
+
+        Env env(*this, envconfig([](std::unique_ptr<Config> cfg) {
+            cfg->FORCE_MULTI_THREAD = true;
+            return cfg;
+        }));
+
+        // Stop the JobQueue
+        env.app().getJobQueue().stop();
+
+        auto runner = env.app().getJobQueue().postCoroTask(
+            jtCLIENT, "CoroTaskTest", [](auto) -> CoroTask<void> { co_return; });
+        BEAST_EXPECT(!runner);
+    }
+
+    void
+    run() override
+    {
+        testVoidCompletion();
+        testCorrectOrder();
+        testIncorrectOrder();
+        testJobQueueAwaiter();
+        testThreadSpecificStorage();
+        testExceptionPropagation();
+        testMultipleYields();
+        testValueReturn();
+        testValueException();
+        testValueChaining();
+        testShutdownRejection();
+    }
+};
+
+BEAST_DEFINE_TESTSUITE(CoroTask, core, xrpl);
+
+}  // namespace test
+}  // namespace xrpl

src/test/core/Coroutine_test.cpp

@@ -40,6 +40,11 @@ public:
         }
     };
 
+    // NOTE: All coroutine lambdas passed to postCoroTask use explicit
+    // pointer-by-value captures instead of [&] to work around a GCC 14
+    // bug where reference captures in coroutine lambdas are corrupted
+    // in the coroutine frame.
+
     void
     correct_order()
     {
@@ -54,13 +59,15 @@ public:
         }));
 
         gate g1, g2;
-        std::shared_ptr<JobQueue::Coro> c;
-        env.app().getJobQueue().postCoro(jtCLIENT, "CoroTest", [&](auto const& cr) {
-            c = cr;
-            g1.signal();
-            c->yield();
-            g2.signal();
-        });
+        std::shared_ptr<JobQueue::CoroTaskRunner> c;
+        env.app().getJobQueue().postCoroTask(
+            jtCLIENT, "CoroTest", [cp = &c, g1p = &g1, g2p = &g2](auto runner) -> CoroTask<void> {
+                *cp = runner;
+                g1p->signal();
+                co_await runner->suspend();
+                g2p->signal();
+                co_return;
+            });
         BEAST_EXPECT(g1.wait_for(5s));
         c->join();
         c->post();
@@ -81,11 +88,17 @@ public:
         }));
 
         gate g;
-        env.app().getJobQueue().postCoro(jtCLIENT, "CoroTest", [&](auto const& c) {
-            c->post();
-            c->yield();
-            g.signal();
-        });
+        env.app().getJobQueue().postCoroTask(
+            jtCLIENT, "CoroTest", [gp = &g](auto runner) -> CoroTask<void> {
+                // Schedule a resume before suspending.  The posted job
+                // cannot actually call resume() until the current resume()
+                // releases CoroTaskRunner::mutex_, which only happens after
+                // the coroutine suspends at co_await.
+                runner->post();
+                co_await runner->suspend();
+                gp->signal();
+                co_return;
+            });
         BEAST_EXPECT(g.wait_for(5s));
     }
 
@@ -101,7 +114,7 @@ public:
         auto& jq = env.app().getJobQueue();
 
         static int const N = 4;
-        std::array<std::shared_ptr<JobQueue::Coro>, N> a;
+        std::array<std::shared_ptr<JobQueue::CoroTaskRunner>, N> a;
 
         LocalValue<int> lv(-1);
         BEAST_EXPECT(*lv == -1);
@@ -118,19 +131,23 @@ public:
 
         for (int i = 0; i < N; ++i)
         {
-            jq.postCoro(jtCLIENT, "CoroTest", [&, id = i](auto const& c) {
-                a[id] = c;
-                g.signal();
-                c->yield();
+            jq.postCoroTask(
+                jtCLIENT,
+                "CoroTest",
+                [this, ap = &a, gp = &g, lvp = &lv, id = i](auto runner) -> CoroTask<void> {
+                    (*ap)[id] = runner;
+                    gp->signal();
+                    co_await runner->suspend();
 
-                this->BEAST_EXPECT(*lv == -1);
-                *lv = id;
-                this->BEAST_EXPECT(*lv == id);
-                g.signal();
-                c->yield();
+                    this->BEAST_EXPECT(**lvp == -1);
+                    **lvp = id;
+                    this->BEAST_EXPECT(**lvp == id);
+                    gp->signal();
+                    co_await runner->suspend();
 
-                this->BEAST_EXPECT(*lv == id);
-            });
+                    this->BEAST_EXPECT(**lvp == id);
+                    co_return;
+                });
             BEAST_EXPECT(g.wait_for(5s));
             a[i]->join();
         }

src/test/core/JobQueue_test.cpp

@@ -43,87 +43,91 @@ class JobQueue_test : public beast::unit_test::suite
         }
     }
 
+    // NOTE: All coroutine lambdas passed to postCoroTask use explicit
+    // pointer-by-value captures instead of [&] to work around a GCC 14
+    // bug where reference captures in coroutine lambdas are corrupted
+    // in the coroutine frame.
+
     void
-    testPostCoro()
+    testPostCoroTask()
     {
         jtx::Env env{*this};
 
         JobQueue& jQueue = env.app().getJobQueue();
         {
-            // Test repeated post()s until the Coro completes.
+            // Test repeated post()s until the coroutine completes.
             std::atomic<int> yieldCount{0};
-            auto const coro = jQueue.postCoro(
-                jtCLIENT,
-                "PostCoroTest1",
-                [&yieldCount](std::shared_ptr<JobQueue::Coro> const& coroCopy) {
-                    while (++yieldCount < 4)
-                        coroCopy->yield();
+            auto const runner = jQueue.postCoroTask(
+                jtCLIENT, "PostCoroTest1", [ycp = &yieldCount](auto runner) -> CoroTask<void> {
+                    while (++(*ycp) < 4)
+                        co_await runner->suspend();
+                    co_return;
                 });
-            BEAST_EXPECT(coro != nullptr);
+            BEAST_EXPECT(runner != nullptr);
 
             // Wait for the Job to run and yield.
             while (yieldCount == 0)
                 ;
 
-            // Now re-post until the Coro says it is done.
+            // Now re-post until the CoroTaskRunner says it is done.
             int old = yieldCount;
-            while (coro->runnable())
+            while (runner->runnable())
             {
-                BEAST_EXPECT(coro->post());
+                BEAST_EXPECT(runner->post());
                 while (old == yieldCount)
                 {
                 }
-                coro->join();
+                runner->join();
                 BEAST_EXPECT(++old == yieldCount);
             }
             BEAST_EXPECT(yieldCount == 4);
         }
         {
-            // Test repeated resume()s until the Coro completes.
+            // Test repeated resume()s until the coroutine completes.
             int yieldCount{0};
-            auto const coro = jQueue.postCoro(
-                jtCLIENT,
-                "PostCoroTest2",
-                [&yieldCount](std::shared_ptr<JobQueue::Coro> const& coroCopy) {
-                    while (++yieldCount < 4)
-                        coroCopy->yield();
+            auto const runner = jQueue.postCoroTask(
+                jtCLIENT, "PostCoroTest2", [ycp = &yieldCount](auto runner) -> CoroTask<void> {
+                    while (++(*ycp) < 4)
+                        co_await runner->suspend();
+                    co_return;
                 });
-            if (!coro)
+            if (!runner)
             {
-                // There's no good reason we should not get a Coro, but we
+                // There's no good reason we should not get a runner, but we
                 // can't continue without one.
                 BEAST_EXPECT(false);
                 return;
             }
 
             // Wait for the Job to run and yield.
-            coro->join();
+            runner->join();
 
-            // Now resume until the Coro says it is done.
+            // Now resume until the CoroTaskRunner says it is done.
             int old = yieldCount;
-            while (coro->runnable())
+            while (runner->runnable())
             {
-                coro->resume();  // Resume runs synchronously on this thread.
+                runner->resume();  // Resume runs synchronously on this thread.
                 BEAST_EXPECT(++old == yieldCount);
             }
             BEAST_EXPECT(yieldCount == 4);
         }
         {
             // If the JobQueue is stopped, we should no
-            // longer be able to add a Coro (and calling postCoro() should
-            // return false).
+            // longer be able to post a coroutine (and calling postCoroTask()
+            // should return nullptr).
             using namespace std::chrono_literals;
             jQueue.stop();
 
-            // The Coro should never run, so having the Coro access this
+            // The coroutine should never run, so having it access this
             // unprotected variable on the stack should be completely safe.
             // Not recommended for the faint of heart...
             bool unprotected;
-            auto const coro = jQueue.postCoro(
-                jtCLIENT, "PostCoroTest3", [&unprotected](std::shared_ptr<JobQueue::Coro> const&) {
-                    unprotected = false;
+            auto const runner = jQueue.postCoroTask(
+                jtCLIENT, "PostCoroTest3", [up = &unprotected](auto) -> CoroTask<void> {
+                    *up = false;
+                    co_return;
                 });
-            BEAST_EXPECT(coro == nullptr);
+            BEAST_EXPECT(runner == nullptr);
         }
     }
 
@@ -132,7 +136,7 @@ public:
     run() override
     {
         testAddJob();
-        testPostCoro();
+        testPostCoroTask();
     }
 };
 

src/test/jtx/impl/AMMTest.cpp

@@ -6,6 +6,7 @@
 
 #include <xrpld/rpc/RPCHandler.h>
 
+#include <xrpl/core/CoroTask.h>
 #include <xrpl/protocol/ApiVersion.h>
 #include <xrpl/protocol/STParsedJSON.h>
 #include <xrpl/resource/Fees.h>
@@ -193,7 +194,6 @@ AMMTest::find_paths_request(
          c,
          Role::USER,
          {},
-         {},
          RPC::apiVersionIfUnspecified},
         {},
         {}};
@@ -215,11 +215,11 @@ AMMTest::find_paths_request(
 
     Json::Value result;
     gate g;
-    app.getJobQueue().postCoro(jtCLIENT, "RPC-Client", [&](auto const& coro) {
+    app.getJobQueue().postCoroTask(jtCLIENT, "RPC-Client", [&](auto) -> CoroTask<void> {
         context.params = std::move(params);
-        context.coro = coro;
         RPC::doCommand(context, result);
         g.signal();
+        co_return;
     });
 
     using namespace std::chrono_literals;

src/xrpld/app/main/Application.cpp

@@ -1425,7 +1425,6 @@ ApplicationImp::setup(boost::program_options::variables_map const& cmdline)
              c,
              Role::ADMIN,
              {},
-             {},
              RPC::apiMaximumSupportedVersion},
             jvCommand};
 

src/xrpld/app/main/GRPCServer.cpp

@@ -3,6 +3,7 @@
 
 #include <xrpl/beast/core/CurrentThreadName.h>
 #include <xrpl/beast/net/IPAddressConversion.h>
+#include <xrpl/core/CoroTask.h>
 #include <xrpl/resource/Fees.h>
 
 namespace xrpl {
@@ -99,13 +100,14 @@ GRPCServerImpl::CallData<Request, Response>::process()
     // ensures that finished is always true when this CallData object
     // is returned as a tag in handleRpcs(), after sending the response
     finished_ = true;
-    auto coro = app_.getJobQueue().postCoro(
-        JobType::jtRPC, "gRPC-Client", [thisShared](std::shared_ptr<JobQueue::Coro> coro) {
-            thisShared->process(coro);
+    auto runner = app_.getJobQueue().postCoroTask(
+        JobType::jtRPC, "gRPC-Client", [thisShared](auto) -> CoroTask<void> {
+            thisShared->processRequest();
+            co_return;
         });
 
-    // If coro is null, then the JobQueue has already been shutdown
-    if (!coro)
+    // If runner is null, then the JobQueue has already been shutdown
+    if (!runner)
     {
         grpc::Status status{grpc::StatusCode::INTERNAL, "Job Queue is already stopped"};
         responder_.FinishWithError(status, this);
@@ -114,7 +116,7 @@ GRPCServerImpl::CallData<Request, Response>::process()
 
 template <class Request, class Response>
 void
-GRPCServerImpl::CallData<Request, Response>::process(std::shared_ptr<JobQueue::Coro> coro)
+GRPCServerImpl::CallData<Request, Response>::processRequest()
 {
     try
     {
@@ -156,7 +158,6 @@ GRPCServerImpl::CallData<Request, Response>::process(std::shared_ptr<JobQueue::C
                  app_.getLedgerMaster(),
                  usage,
                  role,
-                 coro,
                  InfoSub::pointer(),
                  apiVersion},
                 request_};

src/xrpld/app/main/GRPCServer.h

@@ -206,9 +206,12 @@ private:
         clone() override;
 
     private:
-        // process the request. Called inside the coroutine passed to JobQueue
+        /**
+         * Process the gRPC request. Called inside the CoroTask lambda
+         * posted to the JobQueue by process().
+         */
         void
-        process(std::shared_ptr<JobQueue::Coro> coro);
+        processRequest();
 
         // return load type of this RPC
         Resource::Charge

src/xrpld/rpc/Context.h

@@ -3,7 +3,6 @@
 #include <xrpld/rpc/Role.h>
 
 #include <xrpl/beast/utility/Journal.h>
-#include <xrpl/core/JobQueue.h>
 #include <xrpl/server/InfoSub.h>
 
 namespace xrpl {
@@ -24,7 +23,6 @@ struct Context
     LedgerMaster& ledgerMaster;
     Resource::Consumer& consumer;
     Role role;
-    std::shared_ptr<JobQueue::Coro> coro{};
     InfoSub::pointer infoSub{};
     unsigned int apiVersion;
 };

src/xrpld/rpc/ServerHandler.h

@@ -169,13 +169,10 @@ public:
 
 private:
     Json::Value
-    processSession(
-        std::shared_ptr<WSSession> const& session,
-        std::shared_ptr<JobQueue::Coro> const& coro,
-        Json::Value const& jv);
+    processSession(std::shared_ptr<WSSession> const& session, Json::Value const& jv);
 
     void
-    processSession(std::shared_ptr<Session> const&, std::shared_ptr<JobQueue::Coro> coro);
+    processSession(std::shared_ptr<Session> const&);
 
     void
     processRequest(
@@ -183,7 +180,6 @@ private:
         std::string const& request,
         beast::IP::Endpoint const& remoteIPAddress,
         Output&&,
-        std::shared_ptr<JobQueue::Coro> coro,
         std::string_view forwardedFor,
         std::string_view user);
 

src/xrpld/rpc/detail/ServerHandler.cpp

@@ -14,6 +14,7 @@
 #include <xrpl/basics/make_SSLContext.h>
 #include <xrpl/beast/net/IPAddressConversion.h>
 #include <xrpl/beast/rfc2616.h>
+#include <xrpl/core/CoroTask.h>
 #include <xrpl/core/JobQueue.h>
 #include <xrpl/json/json_reader.h>
 #include <xrpl/json/to_string.h>
@@ -284,9 +285,10 @@ ServerHandler::onRequest(Session& session)
     }
 
     std::shared_ptr<Session> detachedSession = session.detach();
-    auto const postResult = m_jobQueue.postCoro(
-        jtCLIENT_RPC, "RPC-Client", [this, detachedSession](std::shared_ptr<JobQueue::Coro> coro) {
-            processSession(detachedSession, coro);
+    auto const postResult = m_jobQueue.postCoroTask(
+        jtCLIENT_RPC, "RPC-Client", [this, detachedSession](auto) -> CoroTask<void> {
+            processSession(detachedSession);
+            co_return;
         });
     if (postResult == nullptr)
     {
@@ -322,17 +324,18 @@ ServerHandler::onWSMessage(
 
     JLOG(m_journal.trace()) << "Websocket received '" << jv << "'";
 
-    auto const postResult = m_jobQueue.postCoro(
+    auto const postResult = m_jobQueue.postCoroTask(
         jtCLIENT_WEBSOCKET,
         "WS-Client",
-        [this, session, jv = std::move(jv)](std::shared_ptr<JobQueue::Coro> const& coro) {
-            auto const jr = this->processSession(session, coro, jv);
+        [this, session, jv = std::move(jv)](auto) -> CoroTask<void> {
+            auto const jr = this->processSession(session, jv);
             auto const s = to_string(jr);
             auto const n = s.length();
             boost::beast::multi_buffer sb(n);
             sb.commit(boost::asio::buffer_copy(sb.prepare(n), boost::asio::buffer(s.c_str(), n)));
             session->send(std::make_shared<StreambufWSMsg<decltype(sb)>>(std::move(sb)));
             session->complete();
+            co_return;
         });
     if (postResult == nullptr)
     {
@@ -373,10 +376,7 @@ logDuration(Json::Value const& request, T const& duration, beast::Journal& journ
 }
 
 Json::Value
-ServerHandler::processSession(
-    std::shared_ptr<WSSession> const& session,
-    std::shared_ptr<JobQueue::Coro> const& coro,
-    Json::Value const& jv)
+ServerHandler::processSession(std::shared_ptr<WSSession> const& session, Json::Value const& jv)
 {
     auto is = std::static_pointer_cast<WSInfoSub>(session->appDefined);
     if (is->getConsumer().disconnect(m_journal))
@@ -443,7 +443,6 @@ ServerHandler::processSession(
                  app_.getLedgerMaster(),
                  is->getConsumer(),
                  role,
-                 coro,
                  is,
                  apiVersion},
                 jv,
@@ -514,18 +513,14 @@ ServerHandler::processSession(
     return jr;
 }
 
-// Run as a coroutine.
 void
-ServerHandler::processSession(
-    std::shared_ptr<Session> const& session,
-    std::shared_ptr<JobQueue::Coro> coro)
+ServerHandler::processSession(std::shared_ptr<Session> const& session)
 {
     processRequest(
         session->port(),
         buffers_to_string(session->request().body().data()),
         session->remoteAddress().at_port(0),
         makeOutput(*session),
-        coro,
         forwardedFor(session->request()),
         [&] {
             auto const iter = session->request().find("X-User");
@@ -562,7 +557,6 @@ ServerHandler::processRequest(
     std::string const& request,
     beast::IP::Endpoint const& remoteIPAddress,
     Output&& output,
-    std::shared_ptr<JobQueue::Coro> coro,
     std::string_view forwardedFor,
     std::string_view user)
 {
@@ -819,7 +813,6 @@ ServerHandler::processRequest(
              app_.getLedgerMaster(),
              usage,
              role,
-             coro,
              InfoSub::pointer(),
              apiVersion},
             params,

src/xrpld/rpc/handlers/RipplePathFind.cpp

@@ -7,6 +7,9 @@
 #include <xrpl/protocol/RPCErr.h>
 #include <xrpl/resource/Fees.h>
 
+#include <condition_variable>
+#include <mutex>
+
 namespace xrpl {
 
 // This interface is deprecated.
@@ -37,98 +40,31 @@ doRipplePathFind(RPC::JsonContext& context)
         PathRequest::pointer request;
         lpLedger = context.ledgerMaster.getClosedLedger();
 
-        // It doesn't look like there's much odd happening here, but you should
-        // be aware this code runs in a JobQueue::Coro, which is a coroutine.
-        // And we may be flipping around between threads.  Here's an overview:
-        //
-        // 1. We're running doRipplePathFind() due to a call to
-        //    ripple_path_find.  doRipplePathFind() is currently running
-        //    inside of a JobQueue::Coro using a JobQueue thread.
-        //
-        // 2. doRipplePathFind's call to makeLegacyPathRequest() enqueues the
-        //    path-finding request.  That request will (probably) run at some
-        //    indeterminate future time on a (probably different) JobQueue
-        //    thread.
-        //
-        // 3. As a continuation from that path-finding JobQueue thread, the
-        //    coroutine we're currently running in (!) is posted to the
-        //    JobQueue.  Because it is a continuation, that post won't
-        //    happen until the path-finding request completes.
-        //
-        // 4. Once the continuation is enqueued, and we have reason to think
-        //    the path-finding job is likely to run, then the coroutine we're
-        //    running in yield()s.  That means it surrenders its thread in
-        //    the JobQueue.  The coroutine is suspended, but ready to run,
-        //    because it is kept resident by a shared_ptr in the
-        //    path-finding continuation.
-        //
-        // 5. If all goes well then path-finding runs on a JobQueue thread
-        //    and executes its continuation.  The continuation posts this
-        //    same coroutine (!) to the JobQueue.
-        //
-        // 6. When the JobQueue calls this coroutine, this coroutine resumes
-        //    from the line below the coro->yield() and returns the
-        //    path-finding result.
-        //
-        // With so many moving parts, what could go wrong?
-        //
-        // Just in terms of the JobQueue refusing to add jobs at shutdown
-        // there are two specific things that can go wrong.
-        //
-        // 1. The path-finding Job queued by makeLegacyPathRequest() might be
-        //    rejected (because we're shutting down).
-        //
-        //    Fortunately this problem can be addressed by looking at the
-        //    return value of makeLegacyPathRequest().  If
-        //    makeLegacyPathRequest() cannot get a thread to run the path-find
-        //    on, then it returns an empty request.
-        //
-        // 2. The path-finding job might run, but the Coro::post() might be
-        //    rejected by the JobQueue (because we're shutting down).
-        //
-        //    We handle this case by resuming (not posting) the Coro.
-        //    By resuming the Coro, we allow the Coro to run to completion
-        //    on the current thread instead of requiring that it run on a
-        //    new thread from the JobQueue.
-        //
-        // Both of these failure modes are hard to recreate in a unit test
-        // because they are so dependent on inter-thread timing.  However
-        // the failure modes can be observed by synchronously (inside the
-        // rippled source code) shutting down the application.  The code to
-        // do so looks like this:
-        //
-        //   context.app.signalStop();
-        //   while (! context.app.getJobQueue().jobCounter().joined()) { }
-        //
-        // The first line starts the process of shutting down the app.
-        // The second line waits until no more jobs can be added to the
-        // JobQueue before letting the thread continue.
-        //
-        // May 2017
+        // makeLegacyPathRequest enqueues a path-finding job that runs
+        // asynchronously.  We block this thread with a condition_variable
+        // until the path-finding continuation signals completion.
+        // If makeLegacyPathRequest cannot schedule the job (e.g. during
+        // shutdown), it returns an empty request and we skip the wait.
+        std::mutex mtx;
+        std::condition_variable cv;
+        bool pathDone = false;
+
         jvResult = context.app.getPathRequests().makeLegacyPathRequest(
             request,
-            [&context]() {
-                // Copying the shared_ptr keeps the coroutine alive up
-                // through the return.  Otherwise the storage under the
-                // captured reference could evaporate when we return from
-                // coroCopy->resume().  This is not strictly necessary, but
-                // will make maintenance easier.
-                std::shared_ptr<JobQueue::Coro> coroCopy{context.coro};
-                if (!coroCopy->post())
+            [&]() {
                 {
-                    // The post() failed, so we won't get a thread to let
-                    // the Coro finish.  We'll call Coro::resume() so the
-                    // Coro can finish on our thread.  Otherwise the
-                    // application will hang on shutdown.
-                    coroCopy->resume();
+                    std::lock_guard lk(mtx);
+                    pathDone = true;
                 }
+                cv.notify_one();
             },
             context.consumer,
             lpLedger,
             context.params);
         if (request)
         {
-            context.coro->yield();
+            std::unique_lock lk(mtx);
+            cv.wait(lk, [&] { return pathDone; });
             jvResult = request->doStatus(context.params);
         }