RFR: 8263896: Remove not_suspended parameter from ObjectMonitor::exit()

[David Holmes]

On Mon, 22 Mar 2021 20:14:49 GMT, Daniel D. Daugherty <dcubed at openjdk.org> wrote:

>> Hi,
>> 
>> Please review the following small patch. The boolean parameter not_suspended is used to detect if we need to set the current JavaThread exiting the monitor as the previous owner (_previous_owner_tid). If not_suspended is true then we set _previous_owner_tid, otherwise we skip the write (modulo the JFR checks). This parameter is always true except when we call exit() from inside enter(). This happens when the JavaThread acquires the monitor but notices that it was suspended while being in the _thread_blocked state. Since in that case the JT was never really "the owner" we skip setting _previous_owner_tid.
>> 
>> This behaviour of releasing the monitor is just an implementation detail of ObjectMonitor::enter() which doesn't need to be exposed in the exit() API. We can identify the same scenario just by checking _current_pending_monitor instead.
>> 
>> Thanks,
>> Patricio
>
> src/hotspot/share/runtime/objectMonitor.cpp line 1182:
> 
>> 1180: #if INCLUDE_JFR
>> 1181:   // set _previous_owner_tid for the MonitorEnter event if it is enabled and
>> 1182:   // the thread isn't releasing the monitor from inside enter()
> 
> nit - need a period and the end of the comment.

This is rather a bit too obscure so I think the comment needs to be expanded.
// Set _previous_owner_tid for the MonitorEnter event if it is enabled and
// we legitimately owned this monitor. We can also get here if we need to self-suspend
// in enter(), in which case we never really owned this monitor and so should not record
// our thread id. In that case current_pending_monitor() is non-NULL.

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PR: https://git.openjdk.java.net/jdk/pull/3101