Merge branch 'notify_one_sleeping_worker' into 'master'

[Runtime] notify only one sleeping worker on new work

See merge request !60

emper/Runtime.cpp

@@ -66,7 +66,7 @@ Runtime::Runtime(workerid_t workerCount, RuntimeStrategy& strategy, unsigned int
 			threads(new pthread_t[workerCount]),
 			workers(new Worker*[workerCount]),
 			randomEngine(seed),
-			atLeastOneWorkerIsSleeping(false),
+			sleepingWorkers(0),
 			skipSleep(false) {
 	const int nprocs = get_nprocs();
 

emper/Runtime.hpp

@@ -57,7 +57,7 @@ class Runtime : public Logger<LogSubsystem::RUNTI> {
 
 	ALIGN_TO_CACHE_LINE std::mutex workerSleepMutex;
 	std::condition_variable workerSleepConditionVariable;
-	ALIGN_TO_CACHE_LINE std::atomic<bool> atLeastOneWorkerIsSleeping;
+	ALIGN_TO_CACHE_LINE std::atomic<unsigned long> sleepingWorkers;
 	bool skipSleep;
 
 	static RuntimeStrategy& DEFAULT_STRATEGY;
@@ -79,15 +79,15 @@ class Runtime : public Logger<LogSubsystem::RUNTI> {
 			// schedules another fiber, when this method will be called
 			// again. And then it is likely that the scheduling worker will
 			// observe the sleeping worker.
-			if (!atLeastOneWorkerIsSleeping.load(std::memory_order_relaxed)) {
+			if (!sleepingWorkers.load(std::memory_order_relaxed)) {
 				return;
 			}
 		}
 
 		std::lock_guard<std::mutex> lk(workerSleepMutex);
 		skipSleep = true;
-		atLeastOneWorkerIsSleeping = false;
-		workerSleepConditionVariable.notify_all();
+		sleepingWorkers.fetch_sub(1, std::memory_order_relaxed);
+		workerSleepConditionVariable.notify_one();
 	}
 
 	void dispatcherLoopSleep() {
@@ -100,7 +100,7 @@ class Runtime : public Logger<LogSubsystem::RUNTI> {
 		// Check again if "skip sleep" has been set.
 		if (skipSleep) return;
 
-		atLeastOneWorkerIsSleeping = true;
+		sleepingWorkers.fetch_add(1, std::memory_order_relaxed);
 		workerSleepConditionVariable.wait(lk);
 	}