CODEWITHSUNDEEP
c#.netmemory-leaksgarbage-collectionwindows-services
ptls44
ptls44

Reputation: 11

GC.Collect() not working when run once a day vs when run continuously

I have a Windows Service. There are 2 projects; the Service project (C#) which houses the service class that has all the timer based code (OnStart, OnStop, Timer_Elapsed etc.) and config files. The other project (VB) has the code on what the service actually does in Manager class.

This windows service has memory leaks and the rate of increase in memory usage is ~50 MB/day. In a month, its memory usage reaches almost 1.5 GB.

Long term, my company plans to implement IDisposable but as a temporary solution we decided to use GC.Collect(). So I added GC.Collect() in timer_elapsed() which is called every 3 seconds since poll_interval = 3. I also set some objects which do not implement IDisposable to null/Nothing.

int counter = 0;

private void Timer_Elapsed()
{
    // create instance of Manager.cs
    try
    {
        // do something
    }
    catch (Exception ex)
    {
        // handle errors
    }
    finally
    {
        Process currentProcess = Process.GetCurrentProcess();
        Logger logger = LogManager.GetCurrentClassLogger();
        logger.Debug("Working Set " + currentProcess.WorkingSet64);

        counter += 1;
        if (counter == counterThreshold)
        {
            counter = 0;
            GC.Collect(GC.MaxGeneration, GCCollectionMode.Forced, true);
            GC.WaitForPendingFinalizers();
            GC.Collect(GC.MaxGeneration, GCCollectionMode.Forced, true);
            logger.Debug("GC");
            logger.Debug("Gen 0: " + GC.CollectionCount(0));
            logger.Debug("Gen 1: " + GC.CollectionCount(1));
            logger.Debug("Gen 2: " + GC.CollectionCount(2));
        }

        currentProcess.Dispose();
        logger = null;

        // set objects to null

        _timer.Start();
    }
}

When counterThreshold is set to 1, memory usage always stays ~28 MB. When it is set to 10, usage stays ~28 MB +/- 0.5 MB. When it is set to 75 (because when poll_interval = 3, timer_elapsed called 20 times/min, so setting counterThreshold to 75 means calling GC.Collect() every 3.75 minutes), I can see that GC.Collect() does not seem to be making much difference. 

12:53:24|SVC.Service1|Working Set 27172864
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12:57:08|SVC.Service1|GC
12:57:08|SVC.Service1|Gen 0: 3
12:57:08|SVC.Service1|Gen 1: 2
12:57:08|SVC.Service1|Gen 2: 2
12:57:11|SVC.Service1|Working Set 31956992
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13:00:54|SVC.Service1|GC
13:00:54|SVC.Service1|Gen 0: 6
13:00:54|SVC.Service1|Gen 1: 4
13:00:54|SVC.Service1|Gen 2: 4
13:00:57|SVC.Service1|Working Set 32673792
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And when counterThreshold is set to 28800 (i.e. call GC.Collect() once a day) increase in memory usage is still ~50 MB/day and calling GC.Collect() seems to have made no difference at all.

memory usage graph

Every time I call GC.Collect(), I expect memory usage to drop to ~28 MB whether I call it continuously or once a day.

  1. What is happening with GC.Collect() as counterThreshold increases/when counterThreshold = 28800?
  2. Why does it work when running continuously vs not work when running once a day?
  3. What I can do with GC so that memory usage drops to ~28 MB whenever I call GC.Collect() irrespective of the value of counterThreshold?

Upvotes: 1

Views: 347

Answers (1)

weichch
weichch

Reputation: 10035

Copied from my comment under the question:

GC.Collect does not solve memory leak issues. It does not destroy objects that are alive / referenced by others. GC.Collect only collects objects in given generations. If you believe you have some objects that can immediately be collected, e.g. a big bitmap that has been closed, calling GC.Collect would help. Otherwise, GC.Collect wouldn't do much.

Furthermore, the fact is garbage collection is running constantly in the background. Calling GC.Collect only forces garbage collection to run now. If there's nothing to collect, memory usage won't drop.

Once per day not works vs run continuously works might be coincidental, that by the time GC.Collect is called once per day, there's nothing to collect, versus running continuously increases the chance of having things to collect.

Upvotes: 1

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