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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