Comment by marginalia_nu | Hacker News Reader

Comment by marginalia_nu | Hacker News Reader

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OpenMP is a compiler flag away.

> Also, that is definitely not the rule? If your problem is parallelizable by nature, parallelism provides massive speedups. Overhead from parallelizing a stream is minimal (effectively nonexistent) now if you leverage Java virtual threads (JDK 21)

This is just not true at all. Not only do virtual threads cope very poorly with I/O other than network I/O, you still get memory barriers. Virtual threads makes the memory overhead lower since you don't need full separate stacks and reduces the cost of spawning new threads, neither of which was ever an issue with streams since they use the common thread pool. Virtual threads don't significantly increase the per-thread performance.

> Not only do virtual threads cope very poorly with I/O other than network I/O, you still get memory barriers.

Which is why I said you probably don't want to use the paradigm I outlined for I/O, but if you did you would want to leverage Java's Managed Blockers and async Completeable Futures for those exact reasons.

> Virtual threads makes the memory overhead lower since you don't need full separate stacks and reduces the cost of spawning new threads, neither of which was ever an issue with streams since they use the common thread pool. Virtual threads don't significantly increase the per-thread performance.

Of course virtual threads don't significantly increase per-thread performance? They make the overhead of spawning multiple threads minimal-to-zero compared to native OS/platform threads, minimizing the cost of jumping from sequential streams to parallel streams. Also, parallel streams don't have to use the global fork join pool, you can use your own fork-join pool? Which is possible in Java, because once again, streams are treated as a first-class citizen and can leverage nearly all other parts of the language efficiently and natively (although I will say Java's verbosity/boilerplateness can suck if you want to leverage your own fork-join pool, but that's widespread complaint of Java not specific to its streams)

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