RFR: 8241234: Unify monitor enter/exit runtime entries

Yudi Zheng yudi.zheng at oracle.com
Fri Mar 27 10:13:18 UTC 2020


Thanks David!

@Yumin, as David said, TRACE_jvmci_3 is implicitly guarded. I personally don’t have problem dropping it.
I think back to then it was for diagnosing some lock issue.

-Yudi

> On 26 Mar 2020, at 23:58, David Holmes <david.holmes at oracle.com> wrote:
> 
> On 27/03/2020 2:36 am, Yumin Qi wrote:
>> HI, Yudi and Coleen
>> jvmciRuntime.cpp:
>>  385 JRT_BLOCK_ENTRY(void, JVMCIRuntime::monitorenter(JavaThread* thread, oopDesc* obj, BasicLock* lock))
>>  386   IF_TRACE_jvmci_3 {
>>  387     char type[O_BUFLEN];
>>  388     obj->klass()->name()->as_C_string(type, O_BUFLEN);
>>  389     markWord mark = obj->mark();
>>  390     TRACE_jvmci_3("%s: entered locking slow case with obj=" INTPTR_FORMAT ", type=%s, mark=" INTPTR_FORMAT ", lock=" INTPTR_FORMAT, thread->name(), p2i(obj), type, mark.value(), p2i(lock));
>>  391     tty->flush();
>>  392   }
>>  393   SharedRuntime::monitor_enter_helper(obj, lock, thread);
>>  394   TRACE_jvmci_3("%s: exiting locking slow with obj=" INTPTR_FORMAT, thread->name(), p2i(obj));
>>  395 JRT_END
>> line 394:
>> first it is not guarded in IF_TRACE_jvmci_3
> 
> It doesn't need to be. An explicit IF_TRACE_jcmvi is only needed to guard code that you don't want to execute unless tracing e.g. setting up the temp buffer as per the preceding code.
> 
>> second I think it should be removed (I am not sure what it means here).
> 
> It is just a logging statement showing the monitor enter has completed - it matches the previous log statement.
> 
> David
> -----
> 
>> Thanks
>> Yumin
>> On 3/26/20 8:22 AM, Yudi Zheng wrote:
>>> 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



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