RFR: 8304074: [JMX] Add an approximation of total bytes allocated on the Java heap by the JVM [v11]

[David Holmes]

On Mon, 8 May 2023 23:13:05 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.
>
> Paul Hohensee has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Implement 32-bit linux Atomic::add()

src/hotspot/share/runtime/atomic.hpp line 310:

> 308: 
> 309:   // Platform-specific implementation of add.  Support for sizes of 4
> 310:   // and 8 bytes are required.  The class must be default constructable,

Comment change seems unnecessary.

src/hotspot/share/services/management.cpp line 2107:

> 2105:     // when result is initialized. The iterator is created and initialized
> 2106:     // before the call to exited_allocated_bytes to ensure we don't miss
> 2107:     // accounting for threads that are just about to terminate.

Sorry this is only accurate if a thread updates `exited_allocated_bytes` after it removes itself from the Threads-list.

src/jdk.management/share/classes/com/sun/management/ThreadMXBean.java line 119:

> 117:      * @implSpec The default implementation throws UnsupportedOperationException
> 118:      * if the Java virtual machine implementation does not support thread
> 119:      * memory allocation measuremust, and otherwise acts as though thread

Typo: measuremust

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PR Review Comment: https://git.openjdk.org/jdk/pull/13814#discussion_r1188021732
PR Review Comment: https://git.openjdk.org/jdk/pull/13814#discussion_r1188023201
PR Review Comment: https://git.openjdk.org/jdk/pull/13814#discussion_r1188022520