Revert "Always use co-routines:"

This reverts commit 3d6e76046c.

src/ripple/rpc/Yield.h

@@ -78,10 +78,15 @@ private:
 struct YieldStrategy
 {
     enum class Streaming {no, yes};
+    enum class UseCoroutines {no, yes};
 
     /** Is the data streamed, or generated monolithically? */
     Streaming streaming = Streaming::no;
 
+    /** Are results generated in a coroutine?  If this is no, then the code can
+        never yield. */
+    UseCoroutines useCoroutines = UseCoroutines::no;
+
     /** How many bytes do we emit before yielding?  0 means "never yield due to
         number of bytes sent". */
     std::size_t byteYieldCount = 0;

src/ripple/rpc/impl/Yield.cpp

@@ -71,6 +71,9 @@ YieldStrategy makeYieldStrategy (Section const& s)
     ys.streaming = get<bool> (s, "streaming") ?
             YieldStrategy::Streaming::yes :
             YieldStrategy::Streaming::no;
+    ys.useCoroutines = get<bool> (s, "use_coroutines") ?
+            YieldStrategy::UseCoroutines::yes :
+            YieldStrategy::UseCoroutines::no;
     ys.byteYieldCount = get<std::size_t> (s, "byte_yield_count");
     ys.accountYieldCount = get<std::size_t> (s, "account_yield_count");
     ys.transactionYieldCount = get<std::size_t> (s, "transaction_yield_count");

src/ripple/server/impl/ServerHandlerImp.cpp

@@ -180,12 +180,24 @@ ServerHandlerImp::onRequest (HTTP::Session& session)
 
     auto detach = session.detach();
 
+    if (setup_.yieldStrategy.useCoroutines ==
+        RPC::YieldStrategy::UseCoroutines::yes)
+    {
         RPC::SuspendCallback suspend (
             [this, detach] (RPC::Suspend const& suspend) {
                 processSession (detach, suspend);
             });
         RPC::Coroutine coroutine (suspend);
         coroutine.run();
+    }
+    else
+    {
+        getApp().getJobQueue().addJob (
+            jtCLIENT, "RPC-Client",
+            [=] (Job&) {
+                processSession (detach, RPC::Suspend());
+            });
+    }
 }
 
 void