RFR: 8304074: [JMX] Add an approximation of total bytes allocated on the Java heap by the JVM [v13]

[David Holmes]

On Thu, 11 May 2023 03:40:31 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Paul Hohensee has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   8304074: getTotalThreadAllocatedBytes name change, increment exited_allocated_bytes in ThreadService::remove_thread, add 64-bit atomic add for linux/bsd_x86, stub out for other platforms
>
> src/hotspot/share/services/management.cpp line 2107:
> 
>> 2105:     // twice, once in the loop and agsin in exited_allocated_bytes if it's
>> 2106:     // removed from the list after it's encountered in the loop but before
>> 2107:     // adding exited_allocated_bytes.
> 
> This is not an accurate description.
> 
> Once we have the TLH we have a fixed set of threads and none of them can update exited_allocated_bytes. If we read exited_allocated_bytes while the TLH is held then the count can be short for two reasons:
> 1. Newly started threads
> 2. Terminating threads that already escaped the TLH but which hadn't updated exited_allocated_bytes by the time we read it.
> AFAICS with the current logic there is no possibility of double-accounting.

Sorry I thought you had made the change to only update exited_allocated_bytes after the thread removed itself from the threads-list. It really makes things so much simpler.

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/13814#discussion_r1190603367