> Here is an attempt to simplify GCLocker implementation for Serial and > Parallel. > > GCLocker prevents GC when Java threads are in a critical region (i.e., > calling JNI critical APIs). JDK-7129164 introduces an optimization that > updates a shared variable (used to track the number of threads in the > critical region) only if there is a pending GC request. However, this also > means that after reaching a GC safepoint, we may discover that GCLocker is > active, preventing a GC cycle from being invoked. The inability to perform GC > at a safepoint adds complexity -- for example, a caller must retry allocation > if the request fails due to GC being inhibited by GCLocker. > > The proposed patch uses a readers-writer lock to ensure that all Java threads > exit the critical region before reaching a GC safepoint. This guarantees that > once inside the safepoint, we can successfully invoke a GC cycle. The > approach takes inspiration from `ZJNICritical`, but some regressions were > observed in j2dbench (on Windows) and the micro-benchmark in > [JDK-8232575](https://bugs.openjdk.org/browse/JDK-8232575). Therefore, > instead of relying on atomic operations on a global variable when entering or > leaving the critical region, this PR uses an existing thread-local variable > with a store-load barrier for synchronization. > > Performance is neutral for all benchmarks tested: DaCapo, SPECjbb2005, > SPECjbb2015, SPECjvm2008, j2dbench, and CacheStress. > > Test: tier1-8
Albert Mingkun Yang has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains six additional commits since the last revision: - Merge branch 'master' into gclocker - review - Merge branch 'master' into gclocker - review - Merge branch 'master' into gclocker - gclocker ------------- Changes: - all: https://git.openjdk.org/jdk/pull/23367/files - new: https://git.openjdk.org/jdk/pull/23367/files/1b6f908b..005087e3 Webrevs: - full: https://webrevs.openjdk.org/?repo=jdk&pr=23367&range=02 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=23367&range=01-02 Stats: 18668 lines in 693 files changed: 10993 ins; 4307 del; 3368 mod Patch: https://git.openjdk.org/jdk/pull/23367.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/23367/head:pull/23367 PR: https://git.openjdk.org/jdk/pull/23367
