RFR: 8227745: Enable Escape Analysis for Better Performance in the Presence of JVMTI Agents

[Richard Reingruber]

On Mon, 14 Sep 2020 04:57:21 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Hi,
>> 
>> this is the continuation of the review of the implementation for:
>> 
>> https://bugs.openjdk.java.net/browse/JDK-8227745
>> https://bugs.openjdk.java.net/browse/JDK-8233915
>> 
>> It allows for JIT optimizations based on escape analysis even if JVMTI agents acquire capabilities to access references
>> to objects that are subject to such optimizations, e.g. scalar replacement. The implementation reverts such
>> optimizations just before access very much as when switching from JIT compiled execution to the interpreter, aka
>> "deoptimization".  Webrev.8 was the last one before before the transition to Git/Github:
>> 
>> http://cr.openjdk.java.net/~rrich/webrevs/8227745/webrev.8/
>> 
>> Thanks, Richard.
>
> src/hotspot/share/compiler/compileBroker.cpp line 831:
> 
>> 829:       MonitorLocker ml(dt, EscapeBarrier_lock, Mutex::_no_safepoint_check_flag);
>> 830:       static int single_thread_count = 0;
>> 831:       enter_single_loop = single_thread_count++ < DeoptimizeObjectsALotThreadCountSingle;
> 
> The update to `single_thread_count` is not atomic.

I think it is atomic because it is never accessed without holding EscapeBarrier_lock

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PR: https://git.openjdk.java.net/jdk/pull/119