如何使用async / await以线程安全的方式从多个线程异步写入文件流

Question

I have an extremely simple logging utility that is currently synchronous. It gets called from UI (WPF) and threadpool threads (Task.Run) and uses lock(_stream){_stream.WriteLine(message);} for thread safety. I'd like to add an asynchronous write method but not sure how to make it threadsafe.

1. Will the following async method work?
2. Will it play nice with the existing synchronous method and can they be used together without issues?
3. Assuming the previous is resolved, should the final Debug.WriteLine go inside the try block or after the finally where it currently is - does it make a difference?

private static SemaphoreSlim _sync = new SemaphoreSlim(1);    

public static async Task WriteLineAsync(string message)
{
    if (_stream != null)
    {
        await _sync.WaitAsync();

        try
        {
            await _stream.WriteLineAsync(string.Format("{0} {1}", DateTime.Now.ToString("HH:mm:ss.fff") + message));
        }
        catch(Exception ex)
        {
            Debug.WriteLine(ex.ToString());
        }
        finally
        {
            _sync.Release();
        }

        Debug.WriteLine("{0} {1}", DateTime.Now.ToString("HH:mm:ss.fff"), message);
    }
}

Answer 1

Will the following async method work?

If the stream is set up properly, then yes, i see no reason why it wouldn't

Will it play nice with the existing synchronous method and can they be used together without issues?

If your synchronous methods use the same SemaphoreSlim and use the synchronous Wait , they should play along nicely.

Assuming the previous is resolved, should the final Debug.WriteLine go inside the try block or after the finally where it currently is - does it make a difference?

If the debug message should be written if and only if the stream successfully writes a message to the stream, it should be inside your try block, after the call to WriteLineAsync .