want your help

[Gary Benson]

Hi Yongqiang,

Yongqiang Yang wrote:
> Hi everyone,
> 
> I am porting hotspot to MIPS.  I meet a bug as follows.
> 
> In function Java_java_lang_ref_Finalizer_invokeFinalizeMethod,
> value of jobject is right when call GetObjectClass and also right
> before return from GetObjectClass . However,  it is wrong when
> calling CallVoidMethod.   For example, It is changed from 0x3e0885d0
> to 0x423ce794.
> Thus, it results in an assert failure below.
> ----------------------------------------------------------------------
>   assert(SharedSkipVerify || obj->is_oop()) failed: sanity check
> ----------------------------------------------------------------------
> 

> I want to know who will change this value from return at GetObjectClass
> to calling CallVoidMethod.  During this time, GC don't run.

> 
> Could anyone have an idea about this?

Look at the source code to jni_GetMethodID and jni_CallVoidMethod,
in hotspot/src/share/vm/prims/jni.cpp.  Notice the JNI_ENTRY and
JNI_END surrounding them?  Look at the source code for JNI_ENTRY,
in hotspot/src/share/vm/runtime/interfaceSupport.hpp.  Do you see
the ThreadInVMfromNative?  That object has a constructor and a
destructor, both of which contain thread state transitions.
Safepoints can occur during those transitions, and oops can change
at any safepoint regardless of whether the GC runs.  You could try
running with -XX:+TraceSafepoint or something like that to see if
one is occuring.

Cheers,
Gary

--
http://gbenson.net/