Add MessageContext message discarding

Allow exception teardown paths to discard pending output messages without asserting that they were sent.

Author: autumn-mck

Framework/Core/include/Framework/MessageContext.h

@@ -466,6 +466,11 @@ class MessageContext
   /// discarded.
   void clear();
 
+  /// Discard pending output messages without asserting that they were sent. This
+  /// is intended for exception teardown paths where normal post-processing will
+  /// not run.
+  void discard();
+
   FairMQDeviceProxy& proxy()
   {
     return mProxy;

Framework/Core/src/MessageContext.cxx

@@ -107,6 +107,13 @@ void MessageContext::clear()
   mMessages.clear();
 }
 
+void MessageContext::discard()
+{
+  mDidDispatch = false;
+  mScheduledMessages.clear();
+  mMessages.clear();
+}
+
 int64_t MessageContext::addToCache(std::unique_ptr<fair::mq::Message>& toCache)
 {
   auto&& cached = toCache->GetTransport()->CreateMessage();