Changed lightweight semaphore to avoid costly sem_timedwait (on Linux) when timeout is 0 (see #210); also fixed error handling in semaphore

Author: cameron314

build/makefile

@@ -29,7 +29,7 @@ tests: bin/unittests$(EXT) bin/fuzztests$(EXT)
 
 benchmarks: bin/benchmarks$(EXT)
 
-bin/unittests$(EXT): ../concurrentqueue.h ../blockingconcurrentqueue.h ../tests/unittests/unittests.cpp ../tests/unittests/mallocmacro.cpp ../tests/common/simplethread.h ../tests/common/simplethread.cpp ../tests/common/systemtime.h ../tests/common/systemtime.cpp ../tests/corealgos.h ../tests/unittests/minitest.h makefile
+bin/unittests$(EXT): ../concurrentqueue.h ../blockingconcurrentqueue.h ../lightweightsemaphore.h ../tests/unittests/unittests.cpp ../tests/unittests/mallocmacro.cpp ../tests/common/simplethread.h ../tests/common/simplethread.cpp ../tests/common/systemtime.h ../tests/common/systemtime.cpp ../tests/corealgos.h ../tests/unittests/minitest.h makefile
 	test -d bin || mkdir bin
 	g++ -std=c++11 -Wall -pedantic-errors -Wpedantic -Wconversion $(OPTS) -fno-elide-constructors ../tests/common/simplethread.cpp ../tests/common/systemtime.cpp ../tests/unittests/unittests.cpp -o bin/unittests$(EXT) $(LD_OPTS)
 

lightweightsemaphore.h

@@ -274,8 +274,11 @@ class LightweightSemaphore
 		if (oldCount > 0)
 			return true;
 		if (timeout_usecs < 0)
-			return m_sema.wait();
-		if (m_sema.timed_wait((std::uint64_t)timeout_usecs))
+		{
+			if (m_sema.wait())
+				return true;
+		}
+		if (timeout_usecs > 0 && m_sema.timed_wait((std::uint64_t)timeout_usecs))
 			return true;
 		// At this point, we've timed out waiting for the semaphore, but the
 		// count is still decremented indicating we may still be waiting on
@@ -311,12 +314,7 @@ class LightweightSemaphore
 		oldCount = m_count.fetch_sub(1, std::memory_order_acquire);
 		if (oldCount <= 0)
 		{
-			if (timeout_usecs < 0)
-			{
-				if (!m_sema.wait())
-					return 0;
-			}
-			else if (!m_sema.timed_wait((std::uint64_t)timeout_usecs))
+			if ((timeout_usecs == 0) || (timeout_usecs < 0 && !m_sema.wait()) || (timeout_usecs > 0 && !m_sema.timed_wait((std::uint64_t)timeout_usecs)))
 			{
 				while (true)
 				{