On Wed, 15 May 2024 15:27:34 GMT, Per Minborg <pminb...@openjdk.org> wrote:
>> # Stable Values & Collections (Internal) >> >> ## Summary >> This PR proposes to introduce an internal _Stable Values & Collections_ API, >> which provides immutable value holders where elements are initialized _at >> most once_. Stable Values & Collections offer the performance and safety >> benefits of final fields while offering greater flexibility as to the timing >> of initialization. >> >> ## Goals >> * Provide an easy and intuitive API to describe value holders that can >> change at most once. >> * Decouple declaration from initialization without significant footprint or >> performance penalties. >> * Reduce the amount of static initializer and/or field initialization code. >> * Uphold integrity and consistency, even in a multi-threaded environment. >> >> For more details, see the draft JEP: https://openjdk.org/jeps/8312611 >> >> ## Performance >> Performance compared to instance variables using two `AtomicReference` and >> two protected by double-checked locking under concurrent access by all >> threads: >> >> >> Benchmark Mode Cnt Score >> Error Units >> StableBenchmark.atomic thrpt 10 259.478 ? >> 36.809 ops/us >> StableBenchmark.dcl thrpt 10 225.710 ? >> 26.638 ops/us >> StableBenchmark.stable thrpt 10 4382.478 ? >> 1151.472 ops/us <- StableValue significantly faster >> >> >> Performance compared to static variables protected by `AtomicReference`, >> class-holder idiom holder, and double-checked locking (all threads): >> >> >> Benchmark Mode Cnt Score >> Error Units >> StableStaticBenchmark.atomic thrpt 10 6487.835 ? >> 385.639 ops/us >> StableStaticBenchmark.dcl thrpt 10 6605.239 ? >> 210.610 ops/us >> StableStaticBenchmark.stable thrpt 10 14338.239 ? >> 1426.874 ops/us >> StableStaticBenchmark.staticCHI thrpt 10 13780.341 ? >> 1839.651 ops/us >> >> >> Performance for stable lists (thread safe) in both instance and static >> contexts whereby we access a single value compared to `ArrayList` instances >> (which are not thread-safe) (all threads): >> >> >> Benchmark Mode Cnt Score >> Error Units >> StableListElementBenchmark.instanceArrayList thrpt 10 5812.992 ? >> 1169.730 ops/us >> StableListElementBenchmark.instanceList thrpt 10 4818.643 ? >> 704.893 ops/us >> StableListElementBenchmark... > > Per Minborg has updated the pull request incrementally with one additional > commit since the last revision: > > Switch to monomorphic StableValue and use lazy arrays src/java.base/share/classes/jdk/internal/lang/stable/StableUtil.java line 152: > 150: StableValueImpl<V> witness = (StableValueImpl<V>) > 151: Holder.UNSAFE.compareAndExchangeReference(elements, > offset, null, stable); > 152: return witness == null ? stable: witness; Suggestion: return witness == null ? stable : witness; ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/18794#discussion_r1602094801
