没有任务等待时如何适当延迟

Question

我有一个任务正在等待属性设置为真（= 已完成）。我收到属性值更改的方式是通过 EventHandler（准确地说是 System.Diagnostics.Process.OutputDataReceived - 它不断读取另一个进程的输出，直到提供正确的输出）。然而，一直检查属性感觉有点低效。我已经尝试添加一个小的延迟，因为我相信如果这样可以节省 CPU 时间，我可以让自己等待，但我读到 .NET 挣扎于小数毫秒。我可以改进这段代码吗？

private ConcurrentBag<string> _allMessages = new ConcurrentBag<string>();

public OutputRetriever()
{
    var process = new System.Diagnostics.Process();
    ...
    process.OutputDataReceived += OutputDataReceived;
    process.Start();
}

public async Task<string[]> GetAllOutput()
{   
    while (!IsCompleted)
    {
        // how to properly wait here?
        // await Task.Delay(TimeSpan.FromTicks(1)); // is this ok?
    }
    return _allMessages.ToArray();
}

private void ConsoleDataReceived(object sender, DataReceivedEventArgs e)
{
    _allMessages.Add(e?.Data);
    if (e?.Data == "success")
    {
        IsCompleted = true;
    }
}

Answer 1

Windows 中的计时器的分辨率约为16 毫秒，因此无法精确实现低于 16 毫秒的任何延迟。这适用于任何计时器 - .NET 计时器只是 Windows 本机计时器的包装器。

创建自定义 TaskCompletionSource<T> 和 return 一个可以等待的 Task，而不是在循环中忙等待。

class OutputRetriever
{
    private readonly ConcurrentBag<string> _allMessages = new ConcurrentBag<string>();

    private readonly TaskCompletionSource<string[]> _taskSource
        = new TaskCompletionSource<string[]>();

    // Note: this method is not async anymore
    public Task<string[]> GetAllOutput()
    {
        // We just return a task that can be awaited
        return _taskSource.Task;
    }

    void ConsoleDataReceived(object sender, DataReceivedEventArgs e)
    {
        _allMessages.Add(e?.Data);
        if (e?.Data == "success")
        {
            // Here we notify that the task is completed by setting the result
            _taskSource.SetResult(_allMessages.ToArray());
        }
    }
}

现在客户可以像往常一样简单地等待结果：

var receiver = new OutputReceiver();
string[] messages = await receiver.GetAllOutput();

没有任务等待时如何适当延迟

How to properly delay when there is no task to wait for

c#

asynchronous

process

task

delay