ThreadPool is a generic thread pool that manages and recycles threads instead of creating them when a task needs to be run on a different thread. Thread pooling saves the virtual machine the work of creating new threads for every short-lived task. In addition, it minimizes the overhead associated with getting a thread started and cleaning it up after it dies. By creating a pool of threads, a single thread from the pool can be reused any number of times for different tasks. This reduces response time because a thread is already constructed and started and is simply waiting for its next task.
Another characteristic of this thread pool is that it is fixed in size at the time of construction. All the threads are started, and then each goes into a wait state until a task is assigned to it. If all the threads in the pool are currently assigned a task, the pool is empty and new requests (tasks) will have to wait before being scheduled to run. This is a way to put an upper bound on the amount of resources any pool can use up. In the future, this class may be enhanced to provide support growing the size of the pool at runtime to facilitate dynamic tuning.