From 645e32b19e73c519a807362a21aa29045b826101 Mon Sep 17 00:00:00 2001
From: Tom Ritchford <tom@swirly.com>
Date: Tue, 28 Jul 2015 16:16:06 -0400
Subject: [PATCH] Fix coroutine suspend

---
 src/ripple/rpc/Context.h                   |  9 +++++++++
 src/ripple/rpc/Yield.h                     |  5 +++--
 src/ripple/rpc/handlers/RipplePathFind.cpp | 12 +++++++-----
 3 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/src/ripple/rpc/Context.h b/src/ripple/rpc/Context.h
index 4660096c9c..0d4feeb15a 100644
--- a/src/ripple/rpc/Context.h
+++ b/src/ripple/rpc/Context.h
@@ -47,6 +47,15 @@ struct Context
     NodeStore::ScopedMetrics metrics;
 };
 
+inline
+void suspend(Context const& context, Continuation const& continuation)
+{
+    if (context.suspend)
+        context.suspend(continuation);
+    else
+        continuation(doNothingCallback);
+}
+
 } // RPC
 } // ripple
 
diff --git a/src/ripple/rpc/Yield.h b/src/ripple/rpc/Yield.h
index 73dffafbc0..1c700e2974 100644
--- a/src/ripple/rpc/Yield.h
+++ b/src/ripple/rpc/Yield.h
@@ -40,8 +40,9 @@ namespace RPC {
 /** Callback: do something and eventually return. */
 using Callback = std::function <void ()>;
 
+/** A non-empty callback that does nothing. */
 static
-Callback const emptyCallback ([] () {});
+Callback const doNothingCallback ([] () {});
 
 /** Continuation: do something, guarantee to eventually call Callback. */
 using Continuation = std::function <void (Callback const&)>;
@@ -115,7 +116,7 @@ Callback suspendForContinuation (
 {
     return suspend
             ? Callback ([=] () { suspend (continuation); })
-            : emptyCallback;
+            : Callback ([=] () { continuation (doNothingCallback); });
 }
 
 } // RPC
diff --git a/src/ripple/rpc/handlers/RipplePathFind.cpp b/src/ripple/rpc/handlers/RipplePathFind.cpp
index 6b2a012a0e..ca651fb743 100644
--- a/src/ripple/rpc/handlers/RipplePathFind.cpp
+++ b/src/ripple/rpc/handlers/RipplePathFind.cpp
@@ -104,13 +104,15 @@ Json::Value doRipplePathFind (RPC::Context& context)
         lpLedger = context.ledgerMaster.getClosedLedger();
 
         PathRequest::pointer request;
-        context.suspend ([&request, &context, &jvResult, &lpLedger]
-                         (RPC::Callback const& c)
+        suspend(context,
+                [&request, &context, &jvResult, &lpLedger]
+                (RPC::Callback const& callback)
         {
             jvResult = getApp().getPathRequests().makeLegacyPathRequest (
-                request, c, lpLedger, context.params);
-            if (! request)
-                c();
+                request, callback, lpLedger, context.params);
+            assert(callback);
+            if (! request && callback)
+                callback();
         });
 
         if (request)