Simple Multi-Threading in Java

Question

Currently, I'm running on a thread-less model that isn't working simply because I'm running out of memory before I can process the data I'm being handed. I've made all the changes that I can to optimize the code, and it's still just not quite quick enough.

Clearly I should move on to a threaded model. I'm wondering what the simplest, easiest way to do the following is:

• The main thread passes some info to the worker
• That worker performs some work that I'll refactor out of the main method
• The workers will disappear and new ones will be instantiated when needed

I've never worked with java threading and from what I've read up on it seems pretty complicated, even if what I'm looking for seems pretty simple.

Answer 1

If you have multiple independent units of work of equal priority, the best solution is generally some sort of work queue, where a limited number of threads (the number chosen to optimize performance) sit in a while(true) loop dequeuing work units from the queue and executing them.

Generally the optimum number of threads is going to be the number of processors +/- 1, though in some cases a larger number will be optimal if the threads tend to get stalled by disk I/O requests or some such.

But keep in mind that tuning the entire system may be required. Eg, you may need more disk arms, and certainly more RAM may be required.

Answer 2

I'd start by having a read through Java Concurrency as refresher ;)

In particular, I would spend some time getting to know the Executors API as it will do most of what you've described without a lot of the overhead of dealing with to many locks ;)

Answer 3

Distributing the memory consumption to multiple threads will not change overall memory consumption. From what I read out of your question, I would like to step forward and tell you: Increase the heap of the Java engine, this will help. Looks like you have to optimize the Java startup parameters and not your code. If I am wrong, then you will have to buffer the data. To Disk! Not to a thread in the same memory model.