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

[serguei.spit...@oracle.com]

Hi Coleen, Thank you for the update 02.incr. I'm Okay with it. There is already a version of the oops_do in the JvmtiThreadState class (but no nmethods_do). But no pressure. It is not clear to me if moving the event queue from Thread to JvmtiThreadState is better (it solves the footprint issue though). So, your is Okay fix now with this small update. Thank you a lot for taking care about it! Thanks, Serguei On 12/4/19 15:06, coleen.phillim...@oracle.com wrote: Hi Serguei, On 12/4/19 5:15 PM, serguei.spit...@oracle.com wrote: Hi Coleen, 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.phillim...@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