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From Ashwin Jayaprakash <ashwin.jayaprak...@gmail.com>
Subject [Native:JNI] jni.Global vs jni.Lock and fatal error at childInit(..) on Linux
Date Tue, 30 Aug 2011 22:22:45 GMT
Hi,
I tried using the jni.Global class to do interprocess locking between 2
processes. I wasn't sure whether to use Global or the Lock class. Both seem
to have identical APIs.

It worked alright on Windows 7. The 2 communicating processes weren't even
parent-child and it still worked.

However, on Linux (Ubuntu 64bit Intel) the child process crashes at
Global.childInit(..) method. Even when the second process was started by
hand (not as a child process of the first using ProcessBuilder) it crashed.
The first few lines of the dump shown below.

The code and a related question I asked a few days ago on the same
forum: [Native:JNI]
Stability, usage and maintenance of shared memory and mutex
code<http://markmail.org/thread/rudbjh7n3knkm4ji>

Questions:

   1. What is the difference between Global and Lock?
   2. How do you use either one of them for inter-process locking - esp. on
   Linux?


JVM dump:

---------------  T H R E A D  ---------------

Current thread (0x08492000):  JavaThread "main" [_thread_in_native, id=9706,
stack(0xb6d10000,0xb6d61000)]

siginfo:si_signo=SIGSEGV: si_errno=0, si_code=1 (SEGV_MAPERR),
si_addr=0x00000000

Registers:
EAX=0x8ee065fc, EBX=0xb4428ff4, ECX=0x00000000, EDX=0x00000000
ESP=0xb6d5fedc, EBP=0xb6d5fef8, ESI=0x0855b4a8, EDI=0x08492118
EIP=0x00000000, CR2=0x00000000, EFLAGS=0x00010282

Top of Stack: (sp=0xb6d5fedc)
0xb6d5fedc:   b4415a76 8ee065fc 08559450 0855b4a8
0xb6d5feec:   b4415a4f 0855b4a8 08551f60 b6d5ff28
0xb6d5fefc:   b4415d90 8ee065fc 0855b4a8 08559450
0xb6d5ff0c:   08492118 b6d5ff78 b780b230 08559450
0xb6d5ff1c:   b4415d60 b6d5ff5c b45f3ff4 b6d5ff78
0xb6d5ff2c:   b45ee1fe b6d5ff5c 0855b4a8 08559450
0xb6d5ff3c:   b6d5ffc4 b6fa4b8d 08492000 084928b0
0xb6d5ff4c:   08559450 084928b4 084928b4 fffffffe

Instructions: (pc=0x00000000)
0xfffffff0:

Stack: [0xb6d10000,0xb6d61000],  sp=0xb6d5fedc,  free space=13fb6d5f860k
Java frames: (J=compiled Java code, j=interpreted, Vv=VM code)
j  org.apache.tomcat.jni.Global.childInit(Ljava/lang/String;J)J+0
j  shm.ShmReader.test()V+48
j  shm.ShmReader.main([Ljava/lang/String;)V+7
v  ~StubRoutines::call_stub


Thanks,
Ashwin.

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