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Back to newsletter 190 contents

Thanks to a nice slide from Azul's Ivan Krylov, I have listed all the JEPs that have performance impact in Java 9. There are lots of low-, feature-, and high-level changes. Starting at the low-level, there's: better contention management - 143; sharing interned Strings across JVMs running G1 - 250; restructured code cache (with some new tuning flags) - 230; faster cryptography using recently available CPU instructions - 246; denser strings - 254; and moving String concatentation optimization from compile-time to runtime - 280.

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At the new feature level we have a JIT-C plugin capability - 243 - yes, you can now replace hotspot with your own compiler! JMH with a benchmark suite is included so you can run benchmarks to compare versions - 230. jcmd will now be able to alter some fine-grained JIT compiler directives at runtime, and of course you can define them statically at startup - 165, this may be particularly useful for those low latency applications with warmup concerns.

At the high level we have Flow* Reactive Streams interfaces - 266 (Flow.Processor, Flow.Publisher, Flow.Subscriber, Flow.Subscription); we have convenience collection factories for creating (immutable) collections - 269, you can now write List l = List.of(a, b, c) or Map m = Map.of(k1, v1, k2, v2), letting you create your collection in a nice easily readable format and also getting a more efficient form because knowing they're immutable means a specialized data structure can be used. It's not minimal perfect hashing yet, but that's doable. And finally, java.lang.invoke.VarHandle gives you properly supported access to capabilities that were previously restricted to sun.misc.Unsafe. This is likely to be the most far-reaching change, with libraries that previously shied away from hacking sun.misc.Unsafe, now converting to use VarHandles. Look at the JEP or VarHandle if you want more detail.

Now on to those JEP links, our usual links to tools, articles, news, talks, blogs. And if you need the tips from this month's articles and talks, as ever they are extracted into this month's tips page.


Java performance tuning related news.


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Jack Shirazi

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Last Updated: 2022-06-29
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