diff options
Diffstat (limited to 'Xamarin.Forms.Core/LockingSemaphore.cs')
-rw-r--r-- | Xamarin.Forms.Core/LockingSemaphore.cs | 51 |
1 files changed, 51 insertions, 0 deletions
diff --git a/Xamarin.Forms.Core/LockingSemaphore.cs b/Xamarin.Forms.Core/LockingSemaphore.cs new file mode 100644 index 00000000..b9fd20a9 --- /dev/null +++ b/Xamarin.Forms.Core/LockingSemaphore.cs @@ -0,0 +1,51 @@ +using System; +using System.Collections.Generic; +using System.Threading; +using System.Threading.Tasks; + +namespace Xamarin.Forms +{ + internal class LockingSemaphore + { + static readonly Task Completed = Task.FromResult(true); + readonly Queue<TaskCompletionSource<bool>> _waiters = new Queue<TaskCompletionSource<bool>>(); + int _currentCount; + + public LockingSemaphore(int initialCount) + { + if (initialCount < 0) + throw new ArgumentOutOfRangeException("initialCount"); + _currentCount = initialCount; + } + + public void Release() + { + TaskCompletionSource<bool> toRelease = null; + lock(_waiters) + { + if (_waiters.Count > 0) + toRelease = _waiters.Dequeue(); + else + ++_currentCount; + } + if (toRelease != null) + toRelease.TrySetResult(true); + } + + public Task WaitAsync(CancellationToken token) + { + lock(_waiters) + { + if (_currentCount > 0) + { + --_currentCount; + return Completed; + } + var waiter = new TaskCompletionSource<bool>(); + _waiters.Enqueue(waiter); + token.Register(() => waiter.TrySetCanceled()); + return waiter.Task; + } + } + } +}
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