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//------------------------------------------------------------------------------
// <copyright file="CountdownTask.cs" company="Microsoft">
// Copyright (c) Microsoft Corporation. All rights reserved.
// </copyright>
//------------------------------------------------------------------------------
namespace System.Web.Util {
using System;
using System.Threading;
using System.Threading.Tasks;
// This class is similar to CountdownEvent, but it uses Task under the covers
// instead of ManualResetEvent. When the internal counter hits zero, the Task
// is marked as complete.
//
// This type is thread-safe. Error checking is not performed in RET builds.
internal sealed class CountdownTask {
private int _pendingCount;
private readonly TaskCompletionSource<object> _tcs = new TaskCompletionSource<object>();
public CountdownTask(int initialCount) {
AddCount(initialCount);
}
public int CurrentCount {
get { return _pendingCount; }
}
public Task Task {
get { return _tcs.Task; }
}
private void AddCount(int delta) {
int newCount = Interlocked.Add(ref _pendingCount, delta);
Debug.Assert(newCount >= 0, "The counter should never hit a negative value.");
if (newCount == 0) {
bool success = _tcs.TrySetResult(null);
Debug.Assert(success, "TrySetResult shouldn't have been already called.");
}
}
public void MarkOperationCompleted() {
AddCount(-1);
}
public void MarkOperationPending() {
AddCount(+1);
}
}
}
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