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by bermanoid 4530 days ago
I hear this sort of claim over and over again. Yet whenever I've had to optimize Java code that does heavy math (particularly work with vectors, matrices, complex numbers, etc) the number one optimization is to more or less maintain my own small object stack, or manually put aside and reuse objects within individual functions. We're talking 10x speed improvements by making sure that garbage created per-iteration is near zero as opposed to just making a mess and letting GC sort it out.

These are objects that have basically no-op constructors, and never stay live for more than a method call, which makes me think that the observed speed boosts must have something to do with GC. Am I missing something?
1 comments
pron 4530 days ago
Yes, vectors is one of those cases where stack allocation has a significant advantage. This will hopefully be resolved (along with cache related issues) when value types are introduced, hopefully in Java 9.
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bermanoid 4526 days ago
Sadly I'm not holding my breath. For the past ten years we've been upvoting requests for value types, being told that they were not necessary because the JVM was brilliant already, then after much argument and ample proof being told that stack allocation in the JVM was a better solution, then having it delayed, finding out that the implementation didn't really work that well, etc. Sun has been pretty shit about prioritizing this issue, perhaps Oracle will be better, but it's a far shittier company than even Sun was so I'm skeptical.

It's also possible I'm jusy raging because this is a problem that has been well known for well over a decade but has been played down by the folks in charge of the JVM every time it comes up, even though it remains a real problem with the platform.

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pron 4525 days ago
The difference is that this time you hear Doug Lea and Brian Goetz talking about this as if it's definitely going into Java 9. This time it's not coming from users but form Oracle. Also theres a JEP and a prototype by John Rose. In fact, it is mention by Oracle as one of the first features of the core platforms planned for 9. This has never been the case before.
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