Java Performance question...

Question

Hi,
I am trying to find information/tips to help me improve overall Java and thread performance using j2sdk 1.4.2 or at least verify I am following good practices regarding performance. I have seen some articles that mention issues w/ synchronized elements, avoiding exception throwing, etc., I still have questions as to if and how the following afffect performance:
- yield() vs. sleep() vs. wait() (or none) for maximizing thread execution time/efficiency
- join() vs. wait() + isAlive()
- static vs. instance methods/data
- Running threads as classes that extend Thread vs. implement Runnable
- ... anything else I may be missing at the moment
Do any of these things even matter?
What about JVM command-line arguments and performance? Is there comprehensive explanation somewhere detailing all options and guidelines on what values to use?
It seems like all of this must have been written about/discussed before, but I haven't seen anything that helps pull it all together so I don't have to experiment with it myself (i.e., reinvent the wheel).

Answer 1

practices regarding performance. I have seen some
articles that mention issues w/ synchronized
elements, avoiding exception throwing, etc.,Take those with a grain of salt.
Sync: Try to keep your synchronized blocks short--get in and get out. This minimizes contention. But don't avoid syncing when you need it or convolute your code just because you think syncing will hurt performance.
Exceptions: If you're throwing so many exceptions that it's significantly hurting performance, you've got bad data, a stupid user, buggy code, a bad network, etc. Avoiding exceptions won't fix that. Throw an exception when it's called for. By definition it should be exceptional, so it won't have a big impact on overall performance.
I still
have questions as to if and how the following afffect
performance:None of the following choices would be made for performance reasons.
>
- yield() vs. sleep() vs. wait() (or none) for
maximizing thread execution time/efficiencyAll of the above serve different purposes. Choose the one that's right for what you're trying to accopmlish.
Yield is for when you want to explicitly give other threads a chance to run. There's no guarantee the will. I've never used it, and I think I've heard that it's rarely usefule and can actually hurt performance a bit, probably because you shouldn't try to outsmart the scheduler.
Sleep is for when you want your thread to stop executing for a certain amount of time.
Wait is for when you want your thread to stop executing until some external event tells it to go back to work.
- join() vs. wait() + isAlive()Join just says stop here until the thread in question exits. I can't think off the top of my head when you'd use wait() + isAlive(), but I doubt there's any performance reason to chose it over join() to accomplish the same task.
- static vs. instance methods/dataNo.
Use static members for things that apply to the class as a whole, and have no need to use or modify the state of a particular instance of the class. Use instance members for things that are related to specific instance--i.e. this Foo as opposed to that Foo. Absolutely DO NOT pick one or the other thinking you'll get better performance.
- Running threads as classes that extend Thread vs.
implement RunnableAre you modifying or adding to Thread's behavior? Almost certainly no. Therefore, your class IS-NOT-A Thread, so don't extend Thread. Implement Runnable. This has nothing to do with performance.
- ... anything else I may be missing at the moment
Do any of these things even matter?It sounds like you're falling into the premature optimization trap.
Use appropriate algorithms and data structures to get maximum performance. Don't futz around with little bitty tweaks that go against good OO or the nature of your design until and unless you have measured the time these sections of code are taking and have verified that they are bottlenecks.
>
What about JVM command-line arguments and
performance? Is there comprehensive explanation
somewhere detailing all options and guidelines on
what values to use? The main things that you tweak on the command line in this respect relate to GC, I think.
http://java.sun.com/docs/hotspot/