Chapter 11: Self-Running Objects

	Chapter 13 - Thread Pooling
	Java Thread Programming
	Paul Hyde


Benefits of Thread Pooling


Thread pooling saves the virtual machine the work of creating brand new threads for every short-lived task. In addition, it minimizes 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 recycled over and over for different tasks .


With the thread pooling technique, you can reduce response time because a thread is already constructed and started and is simply waiting for its next task. In the case of an HTTP server, an available thread in the pool can deliver each new file requested . Without pooling, a brand new thread would have to be constructed and started before the request could be serviced.

Another characteristic of the thread pools discussed in this chapter is that they are fixed in size at the time of construction. All the threads are started, and then each goes into a wait state (which uses very few processor resources) until a task is assigned to it. This fixed size characteristic holds the number of assigned tasks to an upper limit. If all the threads are currently assigned a task, the pool is empty. New service requests can simply be rejected or can be put into a wait state until one of the threads finishes its task and returns itself to the pool. In the case of an HTTP server, this limit prevents a flood of requests from overwhelming the server to the point of servicing everyone very slowly or even crashing. You can expand on the designs presented in this chapter to include a method to support growing the size of the pool at runtime if you need this kind of dynamic tuning.


Toc

Chapter 13 - Thread Pooling