Merge branch 'fix_pipe_sleep_notifyFromAnywhere' into 'master'

[PipeSleepStrategy] fix notifyFromAnywhere

See merge request !277

emper/sleep_strategy/PipeSleepStrategy.hpp

@@ -188,24 +188,32 @@ class PipeSleepStrategy : AbstractWorkerSleepStrategy<PipeSleepStrategy>,
 		// by making the sleepers count negative and thus preventing at least count
 		// sleep attempts.
 
+		int64_t newSleeping;
 		do {
 			// We already prevent enough sleep attempts
 			if (sleeping <= -count) {
 				LOGD("notifyFromAnywhere sleeper count already preventing enough sleep attempts");
 				return;
 			}
-		} while (!sleepers.compare_exchange_weak(sleeping, sleeping - count, std::memory_order_release,
+			// Don't decrease the sleeper count in the CAS loop further than -count,
+			// which is the threshold we need to ensure that the notifications will be
+			// observed.
+			// Decreasing it further than this threshold is not faulty it just
+			// results in unnecessary skipped sleeps.
+			newSleeping = std::max(-count, sleeping - count);
+		} while (!sleepers.compare_exchange_weak(sleeping, newSleeping, std::memory_order_release,
 																						 std::memory_order_acquire));
 
 		stats.incNotify();
 
-		int64_t toWakeup = std::min(sleeping, count);
-		if (sleeping > 0) {
+		// To wakeup should not be negative but could be if sleeping was already negative
+		int64_t toWakeup = std::max(std::min(sleeping, count), 0L);
+		if (toWakeup > 0) {
 			writeNotifications(hint, toWakeup);
 		}
 
 		LOGD("notifyFromAnywhere written "
-				 << toWakeup << " notifications and set sleepers count to: " << sleeping - count);
+				 << toWakeup << " notifications and set sleepers count to: " << newSleeping);
 	}
 
 	template <CallerEnvironment callerEnvironment>