ThreadPool frustrations - Thread creation exceeding SetMaxThreads

user_236476 0
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  • I've got an I/O intensive operation.
  • I only want a MAX of 5 threads ever running at one time.
  • I've got 8000 tasks to queue and complete.
  • Each task takes approximately 15-20seconds to execute.

I've looked around at ThreadPool, but 

        ThreadPool.SetMaxThreads(5, 0);

        List<task> tasks = GetTasks();

        int toProcess = tasks.Count;
        ManualResetEvent resetEvent = new ManualResetEvent(false);

        for (int i = 0; i < tasks.Count; i++)
        {
            ReportGenerator worker = new ReportGenerator(tasks[i].Code, id);
            ThreadPool.QueueUserWorkItem(x =>
            {
                worker.Go();
                if (Interlocked.Decrement(ref toProcess) == 0)
                    resetEvent.Set();
            });
        }

        resetEvent.WaitOne();

I cannot figure out why... my code is executing more than 5 threads at one time. I've tried to setmaxthreads, setminthreads, but it keeps executing more than 5 threads.

What is happening? What am I missing? Should I be doing this in another way?

Thanks

threadpool multithreading c#
5 Answers

There is a limitation in SetMaxThreads in that you can never set it lower than the number of processors on the system. If you have 8 processors, setting it to 5 is the same as not calling the function at all.

user_29609990

Its works for me. This way you can't use a number of workerthreads smaller than "minworkerThreads". The problem is if you need five "workerthreads" maximum and the "minworkerThreads" is six doesn't work. {

ThreadPool.GetMinThreads(out minworkerThreads,out minportThreads);
ThreadPool.SetMaxThreads(minworkerThreads, minportThreads);

}

MSDN

Remarks

You cannot set the maximum number of worker threads or I/O completion threads to a number smaller than the number of processors on the computer. To determine how many processors are present, retrieve the value of the Environment.ProcessorCount property. In addition, you cannot set the maximum number of worker threads or I/O completion threads to a number smaller than the corresponding minimum number of worker threads or I/O completion threads. To determine the minimum thread pool size, call the GetMinThreads method.

If the common language runtime is hosted, for example by Internet Information Services (IIS) or SQL Server, the host can limit or prevent changes to the thread pool size.

Use caution when changing the maximum number of threads in the thread pool. While your code might benefit, the changes might have an adverse effect on code libraries you use.

Setting the thread pool size too large can cause performance problems. If too many threads are executing at the same time, the task switching overhead becomes a significant factor.

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