> # 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 an `AtomicReference` and one > protected by double-checked locking under concurrent access by 8 threads: > > > Benchmark Mode Cnt Score Error Units > StableBenchmark.instanceAtomic avgt 10 1.576 ? 0.052 ns/op > StableBenchmark.instanceDCL avgt 10 1.608 ? 0.059 ns/op > StableBenchmark.instanceStable avgt 10 0.979 ? 0.023 ns/op <- > StableValue (~40% faster than DCL) > > > Performance compared to static variables protected by `AtomicReference`, > class-holder idiom holder, and double-checked locking (8 threads): > > > Benchmark Mode Cnt Score Error Units > StableBenchmark.staticAtomic avgt 10 1.335 ? 0.056 ns/op > StableBenchmark.staticCHI avgt 10 0.623 ? 0.086 ns/op > StableBenchmark.staticDCL avgt 10 1.418 ? 0.171 ns/op > StableBenchmark.staticList avgt 10 0.617 ? 0.024 ns/op > StableBenchmark.staticStable avgt 10 0.604 ? 0.022 ns/op <- > StableValue ( > 2x faster than `AtomicInteger` and DCL) > > > Performance for stable lists in both instance and static contexts whereby the > sum of random contents is calculated for stable lists (which are thread-safe) > compared to `ArrayList` instances (which are not thread-safe) (under single > thread access): > > > Benchmark Mode Cnt Score Error Units > StableListSumBenchmark.instanceArrayList avgt 10 0.356 ? 0.005 ns/op > StableListSumBenchmark.instanceList avgt 10 0.373 ? 0.017 ns/op > <- Stable list > StableListSumBenchmark.staticArrayList avgt 10 0.352 ? 0.002 ns/op > StableListSumBenchmark.staticList avgt 10 0.356 ? 0.00...
Per Minborg has updated the pull request incrementally with one additional commit since the last revision: Add delegation to the thread's exception handler ------------- Changes: - all: https://git.openjdk.org/jdk/pull/18794/files - new: https://git.openjdk.org/jdk/pull/18794/files/d7c31585..7db1101c Webrevs: - full: https://webrevs.openjdk.org/?repo=jdk&pr=18794&range=02 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18794&range=01-02 Stats: 70 lines in 3 files changed: 62 ins; 0 del; 8 mod Patch: https://git.openjdk.org/jdk/pull/18794.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/18794/head:pull/18794 PR: https://git.openjdk.org/jdk/pull/18794
