我创建了一个线程安全的类，该类将a绑定CancellationTokenSource到Task，并保证CancellationTokenSource将在关联Task完成后将其处置。它使用锁来确保CancellationTokenSource遗嘱在处置期间或处置之后不会被取消。发生这种情况是为了遵守文档，其中指出：
Dispose仅当CancellationTokenSource对象上的所有其他操作都已完成时才可以使用该方法。
而且还：
该Dispose方法使CancellationTokenSource处于不可用状态。
这是课程：
public class CancelableExecution
{
private readonly bool _allowConcurrency;
private Operation _activeOperation;
private class Operation : IDisposable
{
private readonly object _locker = new object();
private readonly CancellationTokenSource _cts;
private readonly TaskCompletionSource<bool> _completionSource;
private bool _disposed;
public Task Completion => _completionSource.Task; // Never fails
public Operation(CancellationTokenSource cts)
{
_cts = cts;
_completionSource = new TaskCompletionSource<bool>(
TaskCreationOptions.RunContinuationsAsynchronously);
}
public void Cancel()
{
lock (_locker) if (!_disposed) _cts.Cancel();
}
void IDisposable.Dispose() // Is called only once
{
try
{
lock (_locker) { _cts.Dispose(); _disposed = true; }
}
finally { _completionSource.SetResult(true); }
}
}
public CancelableExecution(bool allowConcurrency)
{
_allowConcurrency = allowConcurrency;
}
public CancelableExecution() : this(false) { }
public bool IsRunning =>
Interlocked.CompareExchange(ref _activeOperation, null, null) != null;
public async Task<TResult> RunAsync<TResult>(
Func<CancellationToken, Task<TResult>> taskFactory,
CancellationToken extraToken = default)
{
var cts = CancellationTokenSource.CreateLinkedTokenSource(extraToken, default);
using (var operation = new Operation(cts))
{
// Set this as the active operation
var oldOperation = Interlocked.Exchange(ref _activeOperation, operation);
try
{
if (oldOperation != null && !_allowConcurrency)
{
oldOperation.Cancel();
await oldOperation.Completion; // Continue on captured context
}
var task = taskFactory(cts.Token); // Run in the initial context
return await task.ConfigureAwait(false);
}
finally
{
// If this is still the active operation, set it back to null
Interlocked.CompareExchange(ref _activeOperation, null, operation);
}
}
}
public Task RunAsync(Func<CancellationToken, Task> taskFactory,
CancellationToken extraToken = default)
{
return RunAsync<object>(async ct =>
{
await taskFactory(ct).ConfigureAwait(false);
return null;
}, extraToken);
}
public Task CancelAsync()
{
var operation = Interlocked.CompareExchange(ref _activeOperation, null, null);
if (operation == null) return Task.CompletedTask;
operation.Cancel();
return operation.Completion;
}
public bool Cancel() => CancelAsync() != Task.CompletedTask;
}
CancelableExecution该类的主要方法是RunAsync和Cancel。默认情况下，不允许并发操作，这意味着调用RunAsync第二次将在开始新操作之前默默取消并等待上一个操作的完成（如果它仍在运行）。
此类可以在任何类型的应用程序中使用。它的主要用法是在UI应用程序中，在带有用于启动和取消异步操作的按钮的窗体中，或者在每次更改选定项时都具有取消和重新启动操作的列表框。这是第一种情况的示例：
private readonly CancelableExecution _cancelableExecution = new CancelableExecution();
private async void btnExecute_Click(object sender, EventArgs e)
{
string result;
try
{
Cursor = Cursors.WaitCursor;
btnExecute.Enabled = false;
btnCancel.Enabled = true;
result = await _cancelableExecution.RunAsync(async ct =>
{
await Task.Delay(3000, ct); // Simulate some cancelable I/O operation
return "Hello!";
});
}
catch (OperationCanceledException)
{
return;
}
finally
{
btnExecute.Enabled = true;
btnCancel.Enabled = false;
Cursor = Cursors.Default;
}
this.Text += result;
}
private void btnCancel_Click(object sender, EventArgs e)
{
_cancelableExecution.Cancel();
}
该RunAsync方法接受一个额外的CancellationToken作为参数，该参数链接到内部创建的CancellationTokenSource。提供此可选令牌可能对提前使用场景有用。