RFR: 8325437: Safepoint polling in monitor deflation can cause massive logs [v2]

[Stefan Karlsson]

On Fri, 9 Feb 2024 10:06:30 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

>> If `-Xlog:monitorinflation=debug` is used and `ObjectSynchronizer::chk_in_use_entry` is called while monitor deflation is safepoint polled/blocked, we can have deflated monitors on the in-use list and we can get a huge number of lines stating:
>> 
>> [10.570s][debug][monitorinflation] WARNING: monitor=0x00007fa1004f8480: in-use monitor is deflated.
>> 
>> 
>> This comes from the following code:
>> 
>> void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
>>                                           int* error_cnt_p) {
>>   if (n->owner_is_DEFLATER_MARKER()) {
>>     // This should not happen, but if it does, it is not fatal.
>>     out->print_cr("WARNING: monitor=" INTPTR_FORMAT ": in-use monitor is "
>>                   "deflated.", p2i(n));
>>     return;
>>   }
>> 
>> 
>> There are tentative plans to rewrite the monitor deflation to unlink deflated monitors from the in-use list *before* the safepoint polls, but I'd like to suggest that we make an interim patch that deletes this warning.
>
> Stefan Karlsson has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:
> 
>  - Merge remote-tracking branch 'upstream/master' into 8325437_monitor_deflation_excessive_logging
>  - 8325437: Safepoint polling in monitor deflation can cause massive logs

Thanks, Aleksey for reviewing. GHA passes, so I'm integrating now.

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PR Comment: https://git.openjdk.org/jdk/pull/17752#issuecomment-1935899835