异步情况下线程同步

SemaphoreSlim.cs

SemaphoreSlim mutex = new SemaphoreSlim(1);

int value;

Task<int> GetNextValueAsync(int current);

async Task UpdateValueAsync()

{

  await mutex.WaitAsync().ConfigureAwait(false);

  try

  {

    value = await GetNextValueAsync(value);

  }

  finally

  {

    mutex.Release();

  }

}