Can anybody explain with examples about why should we use Thread-pools.
I have know about use of threadpools with Executors theoretically.
I have gone through number of tutorials, but I didn't get any practically examples about why should we use Threadpools, it can be newFixedThreadPool or newCachedThreadPool or newSingleThreadExecutor
in terms of scalability and performance .
If anybody explain me with respect to performance and scalability with examples about it?
First off, check this description of thread pools that I wrote yesterday: Android Thread Pool to manage multiple bluetooth handeling threads? (ok, it was about android but it's the same for classic java).
The main use I always seem to find for using a threadpool is that is very nicely manages a very common problem: producer-consumer. In this pattern, someone needs to constantly send work items (the producer) to be processed by someone else (the consumers). The work items are obtained from some stream-like source, like a socket, a database, or a collection of disk files, and needs multiple workers in order to be processed efficiently. The main components identifiable here are:
- the producer: a thread that keeps posting jobs
- a queue where the jobs are posted
- the consumers: worker threads that take jobs from the queue and execute them
In addition to this, synchronization needs to be employed to make all this work correctly, since reading and writing to the queue without synchronization can lead to corrupted and inconsistent data. Also, we need to make the system efficient, since the consumers should not waste CPU cycles when there is nothing to do.
Now this pattern is very common, but to implement it from scratch it takes a considerable effort, which is error prone and needs to be carefully reviewed.
The solution is the thread pool. It very conveniently manages the work queue, the consumer threads and all the synchronization needed. All you need to do is play the role of the producer and feed the pool with tasks!