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

[Stefan Karlsson]

On Wed, 7 Feb 2024 15:35:16 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.

Thanks for reviewing!

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

PR Comment: https://git.openjdk.org/jdk/pull/17752#issuecomment-1934418657