On Sat, 9 Jul 2022 05:19:08 GMT, Ioi Lam <ik...@openjdk.org> wrote:
>> src/hotspot/os/posix/perfMemory_posix.cpp line 796:
>>
>>> 794: if (!is_locked_by_another_process) {
>>> 795: if ((pid == os::current_process_id()) ||
>>> 796: (kill(pid, 0) == OS_ERR && (errno == ESRCH || errno ==
>>> EPERM))) {
>>
>> Thinking about this, I now was confused. AFAICS this code is only ever
>> called from `mmap_create_shared` with the directory containing our own pid.
>> I do not see this called for PIDs from other processes. Why do we handle
>> that case? Or am I overlooking something?
>
> The current JVM process only cleans up stale files in the current user's own
> directory. I.e., /tmp/hsperfdata_bob/. However, when we see a file like
> /tmp/hsperfdata_bob/1234, it's possible that
>
> - 1234 was a JVM process created by bob, but this process died without
> cleaning up
> - A new process 1234 is now running, but it belongs to a different user, john
>
> So if `kill(1234, 0)` fails, the JVM concludes that,
> "/tmp/hsperfdata_bob/1234 must belong to a terminated JVM process owned by
> bob".
>
> I think this is the intention of the code, in spite of what the comment says
> above the `kill` call.
I simplified the code and restructured the comments to be interspersed with the
code. Hopefully that would make the logic a little easier to understand.
Despite the large diff in cleanup_sharedmem_files(), the only actual change is
to `flock` in the middle of the loop, and avoid deleting the file if the
`flock` fails.
I removed this comment
// ... are removed because the resources for such a
// process should be in a different user specific directory.
and replaced it with something more comprehensive which hopefully makes more
sense:
// This directory should be used only by JVM processes owned by the
// current user to store PerfMemory files. Any other files found
// in this directory may be removed.
-------------
PR: https://git.openjdk.org/jdk/pull/9406
