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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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