我的计时器导致我的应用程序挂起吗？

Question

I've been scratching my head for days about this problem. I'm trying to get a timer that restarts the application every 50s. The code basically fetches database items every 50s and does something. However it seems to hang overnight when there has been a long period of inactivity. I've just shown a skeleton of the code below. In the code also theres's a connection to a mysql db, rest hhtpwebrequest, and a ssh using renci.ssh to get to another computer. All these are closed properly.

static void Main(string[] args)
        {
            Timer timer = new Timer(state => workDone(), null, 50000, 50000);
            workDone();
        }

        private static void workDone()
        {


        //Hold program open for next cycle
            Console.ReadLine();

        }

Somewhere towards the end of my code i also used Console.ReadLine(); to hold the program open. Is there a reason why this should hang after a period of inactivity? I have a suspicion it's my code but it may also be the linux box? Will post the whole code if need be. Thank you so much for all your help. Cheers.

Answer 1

I guess you are trying to do this:

private static Timer timer;

static void Main(string[] args)
{
    timer = new Timer(state => workDone(), null, 0, 50000);

    // Hold program open...
    Console.ReadLine();
}

private static void workDone()
{
    // Do work
}

I think that by blocking in the callback you'll eventually use up the threadpool.

From MSDN :

The method specified for callback should be reentrant, because it is called on ThreadPool threads. The method can be executed simultaneously on two thread pool threads if the timer interval is less than the time required to execute the method, or if all thread pool threads are in use and the method is queued multiple times.

In your example the time to execute the callback is taking indefinitely long as it is blocking while waiting for user input.

Answer 2

If you want to perform such computation, I suggest you to have one independent thread that will contain a Sleep(50000) call inside. The reason is that if your computation takes more than 50 seconds you might end up with an overhead.

So in your thread measure the start time, do your computation, measure the end time, then compute the computation time and do a sleep of 50 seconds - "computation time". Ensure that this number is positive and put a 10 second minimum sleep in order to let some slack to the other tasks if the computation was longer than 40 seconds.

Thread thread = new Thread(new ThreadStart(myThreadFunction)); thread.Start();

then:

public void myThreadFunction()
{
    Stopwatch stopWatch = new Stopwatch();

    while(someCondition) { 
        Stopwatch stopWatch = new Stopwatch();
        stopWatch.Start();
        doWork();
        stopWatch.Stop();
        long elapsed = stopWatch.ElapsedMilliseconds;
        if(elapsed < 10000) elapsed = 10000;
        Thread.Sleep(elapsed);
    }
}

**doWork() does not have the ReadLine call.