[UnboundedBlockingMpscQueue] Add another assert

emper/UnboundedBlockingMpscQueue.hpp

@@ -83,10 +83,16 @@ class UnboundedBlockingMpscQueue : public Blockable<LogSubsystem::U_B_MPSC_Q> {
 			});
 			if (!tPopped) {
 				std::lock_guard<std::mutex> lock(queueMutex);
+				// If we observed tPopped to be false without holding the
+				// queueMutex, then the same must be true when holding the
+				// mutex.
+				assert(!tPopped);
+
 				// If 't' isn't already set, then mspcQueue.get() MUST
 				// return an element. Note that a non-lineralizabe
 				// queue may break this invariant.
 				assert(!mpscQueue.empty());
+
 				t = mpscQueue.front();
 				mpscQueue.pop();
 				postRetrieve();