RFR: 8241234: Unify monitor enter/exit runtime entries

[Yudi Zheng]

Thanks for the comment!

Here is the new version: http://cr.openjdk.java.net/~yzheng/8241234/webrev.03/ <http://cr.openjdk.java.net/~yzheng/8241234/webrev.03/>

Differences w.r.t. webrev.00 are that:
1. parameter _obj is now renamed to obj
2. oop obj(_obj) is removed

Many thanks,
Yudi


> On 26 Mar 2020, at 15:25, coleen.phillimore at oracle.com wrote:
> 
> 
> 
> On 3/26/20 9:48 AM, Yudi Zheng wrote:
>> Hi Coleen,
>> 
>> The monitor exit entries are marked with JRT_LEAF which contains 
>> >  debug_only(NoHandleMark __hm;)                                     \
>> 
>> This disallows the creation of Handle within the monitor exit entries.
>> > # A fatal error has been detected by the Java Runtime Environment:
>> > #
>> > #  Internal Error (open/src/hotspot/share/runtime/handles.cpp:35), pid=28631, tid=28687
>> > #  assert(_no_handle_mark_nesting == 0) failed: allocating handle inside NoHandleMark
> 
> You are right.  Thanks for pointing this out.
>> I have uploaded a version that addresses the following comments:
>> 1. Have monitor_enter_helper take Handle as arguments.
>> 2. Avoid using _obj as parameter name as it indicates a field according to the coding conventions.
>> 3. oop obj(_obj); is not necessary as there is an implicit conversion from oopDesc* to oop
>> 
>> See http://cr.openjdk.java.net/~yzheng/8241234/webrev.02/ <http://cr.openjdk.java.net/~yzheng/8241234/webrev.02/>
>> 
> 
> Actually, I apologize that I think I am wrong about making monitor_enter_helper take a Handle because I don't think you can create Handle from a thread that isn't _thread_in_vm.
> 
> +// Handles the uncommon case in locking, i.e., contention or an inflated lock.
> +JRT_BLOCK_ENTRY(void, SharedRuntime::complete_monitor_locking_C(oopDesc* obj, BasicLock* lock, JavaThread* thread))
> +  Handle h_obj(thread, obj);
> +  SharedRuntime::monitor_enter_helper(h_obj, lock, thread);
> +JRT_END
>  
> So I think SharedRuntime::monitor_enter_helper() shouldn't take a Handle and that would allow all paths to have this fast path:
> 
>    if (!SafepointSynchronize::is_synchronizing()) {
>      // Only try quick_enter() if we're not trying to reach a safepoint
>      // so that the calling thread reaches the safepoint more quickly.
> -    if (ObjectSynchronizer::quick_enter(_obj, thread, lock)) return;
> +    if (ObjectSynchronizer::quick_enter(h_obj(), thread, lock)) return;
>    }
> 
> Then create the handle in the JRT_BLOCK_NO_ASYNC where it was. Maybe this gets you back to your original webrev.  Sorry about this.
> 
> Thanks,
> Coleen
> 
>> Let me know if there is any other problem.
>> 
>> Many thanks,
>> Yudi
>> 
>>> On 25 Mar 2020, at 15:49, coleen.phillimore at oracle.com <mailto:coleen.phillimore at oracle.com> wrote:
>>> 
>>> 
>>> 
>>> On 3/24/20 1:14 PM, Yudi Zheng wrote:
>>>> Hi Coleen,
>>>> 
>>>> Thanks for the review! Sorry I missed your email. And thanks Vladimir for the reminder.
>>>> 
>>>>>> I think you should have monitor_enter_helper and maybe monitor_exi_helper both take Handle as arguments.  This looks very strange.
>>>> 
>>>> Shall we change ObjectSynchronizer::exit to accept Handle as argument as well?
>>> 
>>> I think you should.
>>>> 
>>>>>> +void SharedRuntime::monitor_enter_helper(oopDesc* _obj, BasicLock* lock, JavaThread* thread) {
>>>>>> Because it creates a Handle anyway.  We try to eagerly pass Handle so that we don't have to search through the code to make sure there aren't any unhandled oops.
>>>>>> The _obj parameter name doesn't follow coding conventions (I was looking for it to be a field in something).
>>>> 
>>>> I took the parameter name from the original methods:
>>>> JRT_BLOCK_ENTRY(void, SharedRuntime::complete_monitor_locking_C(oopDesc* _obj, BasicLock* lock, JavaThread* thread))
>>>> JRT_LEAF(void, SharedRuntime::complete_monitor_unlocking_C(oopDesc* _obj, BasicLock* lock, JavaThread * THREAD))
>>>> Will Change that.
>>>> 
>>>>>> + oop obj(_obj);
>>>>>> Is there not already a implicit conversion from oopDesc* to oop?
>>>> 
>>>> Also took from the original methods. Will get rid of that.
>>> 
>>> Great. thank you.
>>> Coleen
>>>> 
>>>> Thanks,
>>>> Yudi
>>>> 
>>>>>> Thanks,
>>>>>> Coleen
>>>>>> On 3/20/20 11:03 AM, Yudi Zheng wrote:
>>>>>>> Hello,
>>>>>>> 
>>>>>>> Please review this patch that unifies the monitor enter/exit runtime entries used by C1, C2, and JVMCI.
>>>>>>> 
>>>>>>> https://bugs.openjdk.java.net/browse/JDK-8061553 <https://bugs.openjdk.java.net/browse/JDK-8061553> added support for faster "slow" locking paths.
>>>>>>> These paths are not currently used by JVMCI (or C1) leading to slower performance on programs
>>>>>>> that have a lot of short lived locked sections (such as dacapo:h2).
>>>>>>> 
>>>>>>> This patch creates helper methods based on C2’s monitor enter/exit entries, and shares with the C1,
>>>>>>> JVMCI runtimes. It will prevent these runtimes from missing future updates.
>>>>>>> 
>>>>>>> https://bugs.openjdk.java.net/browse/JDK-8241234 <https://bugs.openjdk.java.net/browse/JDK-8241234>
>>>>>>> http://cr.openjdk.java.net/~yzheng/8241234/webrev.00/ <http://cr.openjdk.java.net/~yzheng/8241234/webrev.00/>
>>>>>>> 
>>>>>>> Many thanks,
>>>>>>> Yudi
>> 
>