Changed MessageBase::post() to return a bool to detect failure in the OS message queue (which can happen under stress on win32), and used this to avoid some messaging classes getting stuck.

modules/juce_events/broadcasters/juce_AsyncUpdater.cpp

@@ -61,7 +61,9 @@ AsyncUpdater::~AsyncUpdater()
 void AsyncUpdater::triggerAsyncUpdate()
 {
     if (activeMessage->shouldDeliver.compareAndSetBool (1, 0))
-        activeMessage->post();
+        if (! activeMessage->post())
+            cancelPendingUpdate(); // if the message queue fails, this avoids getting
+                                   // trapped waiting for the message to arrive
 }
 
 void AsyncUpdater::cancelPendingUpdate() noexcept

modules/juce_events/messages/juce_MessageManager.cpp

@@ -66,12 +66,17 @@ void MessageManager::deleteInstance()
 }
 
 //==============================================================================
-void MessageManager::MessageBase::post()
+bool MessageManager::MessageBase::post()
 {
     MessageManager* const mm = MessageManager::instance;
 
     if (mm == nullptr || mm->quitMessagePosted || ! postMessageToSystemQueue (this))
+    {
         Ptr deleter (this); // (this will delete messages that were just created with a 0 ref count)
+        return false;
+    }
+
+    return true;
 }
 
 //==============================================================================
@@ -158,9 +163,15 @@ void* MessageManager::callFunctionOnMessageThread (MessageCallbackFunction* cons
     jassert (! currentThreadHasLockedMessageManager());
 
     const ReferenceCountedObjectPtr<AsyncFunctionCallback> message (new AsyncFunctionCallback (func, parameter));
-    message->post();
-    message->finished.wait();
-    return message->result;
+
+    if (message->post())
+    {
+        message->finished.wait();
+        return message->result;
+    }
+
+    jassertfalse; // the OS message queue failed to send the message!
+    return nullptr;
 }
 
 //==============================================================================
@@ -275,7 +286,9 @@ bool MessageManagerLock::attemptLock (Thread* const threadToCheck, ThreadPoolJob
     }
 
     blockingMessage = new BlockingMessage();
-    blockingMessage->post();
+
+    if (! blockingMessage->post())
+        return false;
 
     while (! blockingMessage->lockedEvent.wait (20))
     {

modules/juce_events/messages/juce_MessageManager.h

@@ -170,7 +170,7 @@ public:
         virtual ~MessageBase() {}
 
         virtual void messageCallback() = 0;
-        void post();
+        bool post();
 
         typedef ReferenceCountedObjectPtr<MessageBase> Ptr;