On Sat, 18 Oct 2025 00:56:25 GMT, Serguei Spitsyn <[email protected]> wrote:
>> With [JDK-8359110](https://bugs.openjdk.org/browse/JDK-8359110) a framework >> to measure GC CPU time was introduced. >> It will be exposed in JMX as `MemoryMXBean.getTotalGcCpuTime()`. There is >> also interest to get the same performance data from JVMTI. >> The following API's are being added with this enhancement: >> >> Introduce: >> - new capability: `can_get_gc_cpu_time` >> - new JVMTI functions: >> - `jvmtiError GetGCCpuTimerInfo(jvmtiEnv* env, jvmtiTimerInfo* info_ptr)` >> - `jvmtiError GetTotalGCCpuTime(jvmtiEnv* env, jlong* nanos_ptr)` >> >> **CSR**: [8370159](https://bugs.openjdk.org/browse/JDK-8370159): Spec: >> introduce new JVMTI function GetTotalGCCpuTime >> >> Testing: >> - TBD: Mach5 tiers 1-6 > > Serguei Spitsyn has updated the pull request incrementally with one > additional commit since the last revision: > > fix a typo in GetGCCpuTimerInfo: long => jlong src/hotspot/share/prims/jvmtiManageCapabilities.cpp line 95: > 93: jc.can_get_current_thread_cpu_time = 1; > 94: jc.can_get_thread_cpu_time = 1; > 95: jc.can_get_gc_cpu_time = 1; I'm wondering, would a user trying to call `GetTotalGCCpuTime` if `can_get_gc_cpu_time` is not successfully set to 1 be undefined behavior? The specs say "To possess a capability, the agent must add the capability (https://docs.oracle.com/en/java/javase/25/docs/specs/jvmti.html#capability). If yes maybe we can discard the extra call to `os::is_thread_cpu_time_supported` in `JvmtiEnv::GetTotalGCCpuTime`? That seems to align with the pattern to not have that check in the other methods as you pointed out. ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/27879#discussion_r2443399514
