await inside lock

refs:

https://blog.cdemi.io/async-waiting-inside-c-sharp-locks/

https://stackoverflow.com/questions/7612602/why-cant-i-use-the-await-operator-within-the-body-of-a-lock-statement

文章建议使用 信号量来代替lock

//Instantiate a Singleton of the Semaphore with a value of 1. This means that only 1 thread can be granted access at a time.static SemaphoreSlim semaphoreSlim = new SemaphoreSlim(1,1);

//Asynchronously wait to enter the Semaphore. If no-one has been granted access to the Semaphore, code execution will proceed, otherwise this thread waits here until the semaphore is released await semaphoreSlim.WaitAsync();try{    await Task.Delay(1000);}finally{    //When the task is ready, release the semaphore. It is vital to ALWAYS release the semaphore when we are ready, or else we will end up with a Semaphore that is forever locked.    //This is why it is important to do the Release within a try...finally clause; program execution may crash or take a different path, this way you are guaranteed execution    semaphoreSlim.Release();}