jmx-dev RFR: 8304074: [JMX] Add an approximation of JVM process allocated bytes

[David Holmes]

On Thu, 4 May 2023 19:54:57 GMT, Paul Hohensee <phh at openjdk.org> wrote:

> Please review this addition to com.sun.management.ThreadMXBean that returns the total number of bytes allocated on the Java heap since JVM launch by both terminated and live threads.
> 
> Because this PR adds a new interface method, I've updated the JMM_VERSION to 4, but would be happy to update it to 3_1 instead.

src/hotspot/share/services/management.cpp line 2102:

> 2100: JVM_ENTRY(jlong, jmm_GetAllThreadAllocatedMemory(JNIEnv *env))
> 2101:     // There is a race between threads that exit during the loop and calling
> 2102:     // exited_allocated_bytes. If the  result is initialized with exited_allocated_bytes,

If you want a stable and accurate value did you consider holding the Threads_lock while you iterate the threads? Or do it as a safepoint VMop?

src/hotspot/share/services/management.cpp line 2106:

> 2104:     // the loop gets to it and thus not be counted. If, on the other hand and done
> 2105:     // here, exited_allocated_bytes is added after the loop, the final result might be
> 2106:     // "too large" because a thread might be counted twice, once in the loop and agsin

typo agsin

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PR Review Comment: https://git.openjdk.org/jdk/pull/13814#discussion_r1185748115
PR Review Comment: https://git.openjdk.org/jdk/pull/13814#discussion_r1185746920