Core pool size vs maximum pool size in ThreadPoolExecutor

From this blog post:

Take this example. Starting thread pool size is 1, core pool size is5, max pool size is 10 and the queue is 100.

As requests come in,threads will be created up to 5 and then tasks will be added to thequeue until it reaches 100. When the queue is full new threads will becreated up to maxPoolSize. Once all the threads are in use and thequeue is full tasks will be rejected. As the queue reduces, so doesthe number of active threads.

IF running threads > corePoolSize & < maxPoolSize, then create a new Thread if Total task queue is full and new one is arriving.

Form doc:(If there are more than corePoolSize but less than maximumPoolSize threads running, a new thread will be created only if the queue is full.)

Now, Take a simple example,

ThreadPoolExecutor executorPool = new ThreadPoolExecutor(5, 10, 3, TimeUnit.SECONDS, new ArrayBlockingQueue<Runnable>(50));

Here, 5 is the corePoolSize - means Jvm will create new thread for new task for first 5 tasks. and other tasks will be added to the queue until queue is getting full (50 tasks).

10 is the maxPoolSize - JVM can create max 10 threads. Means if there are already 5 task/thread is running and queue is full with 50 pending tasks and if one more new request/task is arriving in queue then JVM will create new thread up to 10 (total threads=previous 5 + new 5);

new ArrayBlockingQueue(50) = is a total queue size - it can queue 50 tasks in it.

once all 10 threads are running and if new task is arriving then that new task will be rejected.

Rules for creating Threads internally by SUN:

1. If the number of threads is less than the corePoolSize, create a new Thread to run a new task.

2. If the number of threads is equal (or greater than) the corePoolSize, put the task into the queue.

3. If the queue is full, and the number of threads is less than the maxPoolSize, create a new thread to run tasks in.

4. If the queue is full, and the number of threads is greater than or equal to maxPoolSize, reject the task.

Hope, This is HelpFul.. and please correct me if i'm wrong...

From the doc:

When a new task is submitted in method execute(java.lang.Runnable), and fewer than corePoolSize threads are running, a new thread is created to handle the request, even if other worker threads are idle. If there are more than corePoolSize but less than maximumPoolSize threads running, a new thread will be created only if the queue is full.

Furthermore:

By setting corePoolSize and maximumPoolSize the same, you create a fixed-size thread pool. By setting maximumPoolSize to an essentially unbounded value such as Integer.MAX_VALUE, you allow the pool to accommodate an arbitrary number of concurrent tasks. Most typically, core and maximum pool sizes are set only upon construction, but they may also be changed dynamically using setCorePoolSize(int) and setMaximumPoolSize(int).