获取互斥量后调用await操作 [英] Calling await operation after acquiring mutex

问题描述

如何在获取 mutex 后使用 await FileIO.WriteTextAsync()(在 Windows Phone 8.1 中)写入文件，以便没有两个线程访问同一个文件并且确保互斥.我正在做以下事情:

How can I write to a file using await FileIO.WriteTextAsync() (in Windows Phone 8.1) after acquiring mutex so that no two threads access the same file and mutual exclusion is ensured. I'm doing the following:

mutex.WaitOne()

try
{
    await FileIO.WriteTextAsync(filename, text);
    Debug.WriteLine("written");
}
finally
{
    mutex.ReleaseMutex();
}

但该方法仅适用于一两次迭代，之后它会抛出一个System.Exception.此外，如果我删除 await 关键字或完全删除文件写入方法，代码运行得非常好.所以，所有的麻烦都是由调用异步方法引起的.我该怎么做才能解决这个问题?

But the method works for one or two iterations only, after which it throws a System.Exception. Also, if I remove the await keyword or remove the file writing method entirely, the code runs perfectly fine. So, all trouble is caused by calling an async method. What can I do to resolve this?

推荐答案

这是一个监视器的工作(或者为了使它更异步友好，一个信号量)，而不是一个互斥锁.

This is a job for a monitor (or to make this more async-friendly, a semaphore), not a mutex.

问题是 WriteTextAsync 的延续很可能在一个单独的线程上运行，所以它不能释放互斥量 - 这只能从与最初获取互斥锁的线程相同.

The problem is that the continuation to WriteTextAsync is likely to run on a separate thread, so it can't release the mutex - that can only be done from the same thread that originally acquired the mutex.

var semaphore = new SemaphoreSlim(1);

await semaphore.WaitAsync();

try
{
    await FileIO.WriteTextAsync(filename, text);
    Debug.WriteLine("written");
}
finally
{
    semaphore.Release();
}

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