RFR: 8257831: Suspend with handshakes [v8]

[Robbin Ehn]

On Wed, 14 Apr 2021 16:05:39 GMT, Daniel D. Daugherty <dcubed at openjdk.org> wrote:

>> Robbin Ehn has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fixed flag undef dep + spelling error
>
> src/hotspot/share/runtime/handshake.hpp line 99:
> 
>> 97:   // but we need to check for a safepoint before.
>> 98:   // (this is due to a suspension handshake which put the JavaThread in blocked
>> 99:   // state so a safepoint may be in-progress)
> 
> nit: s/(this/(This/
> nit: s/in-progress)/in-progress.)/

Fixed

> src/hotspot/share/runtime/handshake.hpp line 166:
> 
>> 164:   // thread gets suspended again (after a resume)
>> 165:   // and we have not yet processed it.
>> 166:   bool _async_suspend_handshake;
> 
> Does this need to be `volatile`?

No, _async_suspend_handshake is now only loaded/stored with mutex held.

> src/hotspot/share/runtime/handshake.hpp line 177:
> 
>> 175:   void set_suspended(bool to)               { return Atomic::store(&_suspended, to); }
>> 176:   bool has_async_suspend_handshake()        { return _async_suspend_handshake; }
>> 177:   void set_async_suspend_handshake(bool to) { _async_suspend_handshake = to; }
> 
> Does this need to be an Atomic::store?

No, _async_suspend_handshake is now only loaded/stored with mutex held.

> src/hotspot/share/runtime/objectMonitor.cpp line 424:
> 
>> 422:         // thread that suspended us.
>> 423:         _recursions = 0;
>> 424:         _succ = NULL;
> 
> You might want to add a comment here:
> // Don't need a full fence after clearing successor here because of the call to exit().

Fixed

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

PR: https://git.openjdk.java.net/jdk/pull/3191