.NetCore - 使用 Semaphoreslim 的异步记录器

Question

I am trying to create a logic based on requirements below.

• The class should output to a file
• The class must preserve the order of the messages
• Calling Log does not block calling thread
• Calling Log must be thread safe (will be called from multiple threads)

Sample code i tried is below

 Ilogger log = new Logger();

Thread t1 = new Thread(LongRunningTask);
Thread t2 = new Thread(LongRunningTask2);
t1.Start();
t2.Start();

Console.WriteLine("Hello, World!");

async void LongRunningTask()
{

    for (int i = 0; i < 10; i++)
    {
        await log.Info("Thread-1 - " + i.ToString());
    }

}

async void LongRunningTask2()
{

    for (int i = 0; i < 10; i++)
    {
        await log.Info("Thread-2 - " + i.ToString());
    }

}

Logger Concrete class implementation

internal class Logger : Ilogger
    {
        SemaphoreSlim semaphoreSlim = new SemaphoreSlim(1);
        public async Task Info(string message)
        {
            
            try
            {
                await semaphoreSlim.WaitAsync();
                Console.WriteLine(message);
                
                //await File.WriteAllTextAsync("C://test.txt", message);
            }
            finally
            {
                semaphoreSlim.Release();
            }
        }

    }

Console output seems to be fine. I am getting messages in order. But if i tried to write to a file am getting error as

The process cannot access the file 'C:\test.txt' because it is being used by another process

Can anyone help me understand what I am doing wrong here?

Update:

Actually the problem is with File.WriteAllText - it will override what's already in. Replaced with

File.AppendAllTextAsync - working fine now

Answer 1

Try using this to create your SemaphoreSlim

SemaphoreSlim semaphoreSlim = new SemaphoreSlim(1,1);

This basically works as a mutex now - allowing only one thread at a time.