RFR (M) 8212160: JVMTI agent crashes with "assert(_value != 0LL) failed: resolving NULL _value"

[coleen.phillimore at oracle.com]

Thanks Dan.  I moved the field.  For some reason I thought that class 
did more/different things than hold per-thread information.

I've retested this version with tiers 2-6.

incr webrev at 
http://cr.openjdk.java.net/~coleenp/2019/8212160.03.incr/webrev
full  webrev at http://cr.openjdk.java.net/~coleenp/2019/8212160.03/webrev

Thanks to Serguei for offline discussion.

Coleen

On 12/4/19 7:40 PM, Daniel D. Daugherty wrote:
> Generally speaking, JVM/TI related things should be in JvmtiThreadState
> instead of directly in the Thread class. That way the extra space is only
> consumed when JVM/TI is in use and only when a Thread does something that
> requires a JvmtiThreadState to be created.
>
> Please reconsider moving _jvmti_event_queue.
>
> Dan
>
>
> On 12/4/19 6:06 PM, coleen.phillimore at oracle.com wrote:
>>
>> Hi Serguei,
>>
>> On 12/4/19 5:15 PM, serguei.spitsyn at oracle.com wrote:
>>> Hi Collen, (no problem)
>>>
>>> It looks good in general.
>>> Thank you a lot for sorting this out!
>>>
>>> Just a couple of comments.
>>>
>>>
>>> http://cr.openjdk.java.net/~coleenp/2019/8212160.01/webrev/src/hotspot/share/runtime/thread.hpp.frames.html
>>> 1993 protected:
>>> 1994 // Jvmti Events that cannot be posted in their current context.
>>> 1995 // ServiceThread uses this to collect deferred events from 
>>> NonJava threads
>>> 1996 // that cannot post events.
>>> 1997 JvmtiDeferredEventQueue* _jvmti_event_queue;
>>>
>>> As David I also have a concern about footprint of having the 
>>> _jvmti_event_queue field in the Thread class.
>>> I'm thinking if it'd be better to move this field into the 
>>> JvmtiThreadState class.
>>> Please, see jvmti_thread_state() and 
>>> JvmtiThreadState::state_for(JavaThread *thread).
>>
>> The reason I have it directly in JavaThread is so that the GC oops_do 
>> and nmethods_do code can find it easily.  I like your idea of hiding 
>> it in jvmti but this doesn't seem good to have this code know about 
>> jvmtiThreadState, which seems to be a queue of Jvmti states.  I also 
>> don't want to have jvmtiThreadState to have to add an oops_do() or 
>> nmethods_do() either.
>>
>>>
>>>
>>> http://cr.openjdk.java.net/~coleenp/2019/8212160.01/webrev/src/hotspot/share/prims/jvmtiImpl.cpp.frames.html
>>> 973 void JvmtiDeferredEvent::post(JvmtiEnv* env) {
>>> 974 assert(_type == TYPE_COMPILED_METHOD_LOAD, "only user of this 
>>> method");
>>> 975 nmethod* nm = _event_data.compiled_method_load;
>>> 976 JvmtiExport::post_compiled_method_load(env, nm);
>>> 977 }
>>>
>>> The JvmtiDeferredEvent::post name looks too generic as it posts 
>>> compiled load events only.
>>> Do you consider this function extended in the future to support more 
>>> event types?
>>>
>>
>> I don't envision an extension for this function but I do for 
>> JvmtiDeferredEventQueue::post().  I have a small enhancement that 
>> would handoff the entire queue to the ServiceThread and have it call 
>> post() to post all the events rather than one at a time.
>>
>> So I'll rename this one post_compiled_method_load_event() and leave 
>> the other post() as is for now.
>>
>> open webrev at 
>> http://cr.openjdk.java.net/~coleenp/2019/8212160.02.incr/webrev
>>
>> Thanks,
>> Coleen
>>
>>
>>>
>>> Thanks,
>>> Serguei
>>>
>>>
>>> On 11/26/19 06:22, coleen.phillimore at oracle.com wrote:
>>>> Summary: Add local deferred event list to thread to post events 
>>>> outside CodeCache_lock.
>>>>
>>>> This patch builds on the patch for JDK-8173361.  With this patch, I 
>>>> made the JvmtiDeferredEventQueue an instance class (not AllStatic) 
>>>> and have one per thread.  The CodeBlob event that used to drop the 
>>>> CodeCache_lock and raced with the sweeper thread, adds the events 
>>>> it wants to post to its thread local list, and processes it outside 
>>>> the lock.  The list is walked in GC and by the sweeper to keep the 
>>>> nmethods from being unloaded and zombied, respectively.
>>>>
>>>> Also, the jmethod_id field in nmethod was only used as a boolean so 
>>>> don't create a jmethod_id until needed for 
>>>> post_compiled_method_unload.
>>>>
>>>> Ran hs tier1-8 on linux-x64-debug and the stress test that crashed 
>>>> in the original bug report.
>>>>
>>>> open webrev at 
>>>> http://cr.openjdk.java.net/~coleenp/2019/8212160.01/webrev
>>>> bug link https://bugs.openjdk.java.net/browse/JDK-8212160
>>>>
>>>> Thanks,
>>>> Coleen
>>>
>>
>

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