c# - Monitor.TryEnter 不起作用

Question

我的部分代码隐藏:

object _sync = new object();

private async void OnKeyDown(object sender, KeyEventArgs e) {
    if (!Monitor.TryEnter(_sync)) return;

    Trace.Write("taken...");
    await Task.Delay(TimeSpan.FromSeconds(5));
    Trace.WriteLine(" done");

    Monitor.Exit(_sync);
}

输出(在不到 5 秒内按几次):

taken...taken...taken... done
done
done

怎么会？？ _sync 锁从未被占用，为什么？

Answer 1

混合使用 Monitor 和 await 是……有点冒险。看起来您正在尝试做的是确保它一次只运行一次。我怀疑 Interlocked 可能更简单:

object _sync = new object();
int running = 0;
private async void OnKeyDown(object sender, KeyEventArgs e) {
    if(Interlocked.CompareExchange(ref running, 1, 0) != 0) return;

    Trace.Write("taken...");
    await Task.Delay(TimeSpan.FromSeconds(5));
    Trace.WriteLine(" done");

    Interlocked.Exchange(ref running, 0);
}

请注意，您可能还想考虑如果发生错误等会发生什么；值如何重置？您可能可以使用 try/finally:

if(Interlocked.CompareExchange(ref running, 1, 0) != 0) return;

try {
    Trace.Write("taken...");
    await Task.Delay(TimeSpan.FromSeconds(5));
    Trace.WriteLine(" done");
} finally {
    Interlocked.Exchange(ref running, 0);
}