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From "cyang.cq" <cyang...@gmail.com>
Subject Re: [drlvm]program takes forever to exit when using GCV4.1 in r553700
Date Fri, 31 Aug 2007 08:01:01 GMT
It seems to be caused by commit 549899 for HAROMNY-3864. 
This commit introduced a global lock  to guard the methods of 
java.lang.ThreadGroup. And due to the global lock, adaemon thread 
may now block the vm_destroy process.

 To my knowledge, vm_destroy calls vm_shutdown_stop_java_threads
 to stop all the daemon threads, which registers safepoint_callback
(vm_shutdown_callback) for each daemon thread. At a safe point, 
vm_shutdown_callback calls hythread_exit to stop a thread directly. 

The problem is that, a daemon thread may exit spontaneously during this 
process. The run method of the thread returns, java.lang.Thread.detach is 
then called, which in turn calls ThreadGroup.remove, where the global lock 
is acquired. If the thread encounters a safe point, before the release of the 
lock, and the vm_shutdown_callback has been registered, bad thing happens: 
the daemon thread quits directly, the lock never gets released. The non-daemon 
thread who initiates the vm shutdown process, will then be blocked forever, 
when it calls java.lang.Thread.detach to detach itself.

And in the gcv4.1's case, the daemon thread makes this happen is the instance 
of java.lang.FinalizerThread. It is supposed to be shut down by 
exec_shutdown_sequence. However, exec_shutdown_sequence doesn't wait 
for its termination before returning.

Any ideas?
Thanks.

  

 
    
----- Original Message ----- 
From: "Xiao-Feng Li" <xiaofeng.li@gmail.com>
To: <dev@harmony.apache.org>
Sent: Monday, August 27, 2007 10:54 AM
Subject: Re: [drlvm]program takes forever to exit when using GCV4.1 in r553700


> Looks like GCv4.1 is not covered by the daily regression testing. It
> should be some issues introduced in other modules. Since GCv4.1 is not
> actively maintained now, if possible, please try to use the default
> GCv5. I'd be happy to answer you questions about it.
> 
> Thanks,
> xiaofeng
> 
> On 8/26/07, cyang.cq <cyang.cq@gmail.com> wrote:
>> Hi, all
>> I checked out r553700 about one month ago. And I find that a program
>> sometimes takes forever to exit when using GCV4.1.
>>
>> A simple HelloWorld.java below is enough to reproduce this problem.
>>
>> public class HelloWorld{
>>    public static void main(String[] argv){
>>       System.out.println("Hello, world!");
>>    }
>> }
>>
>> java -XX:gc.dll=libgc_cc.so HelloWorld
>>
>> The "Hello, world!" can be printed out, but the program then enters dead loop.
>> It seems to be blocked forever when trying to acquire the lock in
>> java.lang.Thread.detach();
>>
>> My configuration is:
>> drlvm: svn = r553700, (Aug 26 2007), Linux/ia32/gcc 3.4.3, debug/release build
>> OS:    Red Hat Enterprise Linux AS release 4 (Nahant)
>>        Kernel 2.6.9-5.ELsmp on an i686
>> CPU:   4 X Intel(R) Xeon(TM) CPU 3.20GHz
>>
>>
>> Any suggestions?
>>
>> Thanks in advance.
> 
> 
> -- 
> http://xiao-feng.blogspot.com
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