On Fri, 14 Nov 2025 21:21:16 GMT, Jonas Norlinder <[email protected]> wrote:
>> Hi all, >> >> This PR augments the CPU time sampling measurement capabilities that a user >> can perform from Java code with the addition of >> `MemoryMXBean.getGcCpuTime()`. With this patch it will be possible for a >> user to measure process and GC CPU time during critical section or >> iterations in benchmarks to name a few. This new method complements the >> existing `OperatingSystemMXBean.getProcessCpuTime()` for a refined >> understanding. >> >> `CollectedHeap::gc_threads_do` may operate on terminated GC threads during >> shutdown, but thanks to JDK-8366865 by @walulyai we can piggyback on the new >> `Universe::is_shutting_down`. I have implemented a stress-test >> `test/jdk/java/lang/management/MemoryMXBean/GetGcCpuTime.java` that may >> identify reading CPU time of terminated threads. Synchronizing on >> `Universe::is_shutting_down` and `Heap_lock` resolves this problem. >> >> FWIW; To my understanding we don't want to add a >> `Universe::is_shutting_down` check in gc_threads_do as this may introduce a >> performance penalty that is unacceptable, therefore we must be careful about >> the few places where external users call upon gc_threads_do and may race >> with a terminating VM. >> >> Tested: test/jdk/java/lang/management/MemoryMXBean/GetGcCpuTime.java, >> jdk/javax/management/mxbean hotspot/jtreg/vmTestbase/nsk/monitoring on Linux >> x64, Linux aarch64, Windows x64, macOS x64 and macOS aarch64 with release >> and fastdebug. > > Jonas Norlinder has updated the pull request incrementally with one > additional commit since the last revision: > > Revert "Reduce GC coverage for trivial API test" > > This reverts commit 8fd1ee093066138c9aa5602dcac0e7db1916db6b. Marked as reviewed by kevinw (Reviewer). ------------- PR Review: https://git.openjdk.org/jdk/pull/27537#pullrequestreview-3472086274
