SemaphoreLight

Qoollo SemaphoreLight

Semaphore is a synchronization primitive that control the access to limited resource.

BCL already have 2 implementations of this primitive: System.Threading.Semaphore and System.Threading.SemaphoreSlim. But they are not as fast as possible. System.Threading.Semaphore use the Windows semaphore under cover so it should call WinAPI which gives an overhead. System.Threading.SemaphoreSlim is support async Wait method (which require additional checks) and also badly implemented.

SemaphoreLight provide a similar API but outperform standard implementations all the time. This is because it works in lock-free manner when possible.

Sample code:

var sem = new SemaphoreLight(0);

// Release and wait
sem.Release();
sem.Wait();

// Release and wait with timeout and CancellationToken
sem.Release();
sem.Wait(0, CancellationToken.None);

Performance

All tests performed on CPU with 8 cores. Every iteration has pause for 10 processor ticks (Thread.Spin(10)).

Release thread count / Wait thread count	SemaphoreLight	SemaphoreSlim	Semaphore
1 / 1	980 ms	1700 ms	3670 ms
8 / 8	650 ms	1700 ms	3500 ms
1 / 8	1750 ms	3700 ms	6900 ms
4 / 16	870 ms	2800 ms	4800 ms
8 / 1	520 ms	1240 ms	3450 ms
16 / 4	550 ms	1300 ms	3200 ms