Question

From javadoc for ThreadPoolExecutor:

When a new task is submitted in method execute(java.lang.Runnable)
…. If there are more than corePoolSize but less than
maximumPoolSize threads running, a new thread will be created only if
the queue is full.

How can I make ThreadPool that will start new thread instead of submitting task to queue in this situation?

Example:

I have thread with corePoolSize=5 and maxPoolSize=10 and unbounded queue.

Suppose corePoolSize threads is busy right now, and new task is arrived – pool must start new thread and execute new task.

Suppose maxPoolSize threads is busy right now, and new task is arrived – pool must persist task into queue, and first free thread must take this task and execute.

Answer 1

If you want a thread pool with a maximum size where the tasks are queued only when all the threads are busy.

ExecutorService service = Executors.newFixedThreadPool(numberOfThreads);

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The cached thread pool which will not queue tasks, but will create a new thread as required. It will re-use a thread if one is free.

ExecutorService service = Executors.newCachedThreadPool();