ThreadPoolExecutor : Tasks are getting queued up and not submitted

Question

We have a scenario where tasks submitted to ThreadPoolExecutor are long running. When the thread pool is started we start it with core pool size = 5, max pool size = 20 and queu

Answer 1

I think another approach would be to set the corePoolSize based on the the number of tasks waiting in the queue. One can control the corePoolSize by using setCorePoolSize. A sample monitor thread can control you threadPoolExecutor. You can also improve this monitor to adjust the degree of parallelism.

    public class ExecutorMonitor extends Thread{

            ThreadPoolExecutor executor = null;
            int initialCorePoolSize;
            public ExecutorMonitor(ThreadPoolExecutor executor)
            {
                this.executor = executor;
                this.initialCorePoolSize = executor.getCorePoolSize();
            }
            @Override
            public void run()
            {
                while (true)
                {   
                    try {
                        Thread.sleep(5000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    if (executor.getQueue().size() > 0)
                    {
                        if(executor.getActiveCount() < executor.getMaximumPoolSize())
                            executor.setCorePoolSize(executor.getCorePoolSize() + 1);
                    }
                    if (executor.getQueue().size() == 0)
                    {
                        if(executor.getCorePoolSize() > initialCorePoolSize)
                            executor.setCorePoolSize(executor.getCorePoolSize() -1);
                    }
                }
            }
        }