Re: [bdbxml] Crash in dbxml_javaJNI.XmlResults_next__SWIG_0

Thomas,

The problem is that your main thread of execution is
closing the container and manager before the child
threads are through with them.

This results in deallocating objects and resources out from
underneath the child threads and unpredictable things
happen when freed memory is accessed in the underlying
C++ code.

You need to manage your threads and ensure that none of
them are still using BDB XML resources when you close
the container and manager.

I believe that others have seen this problem, and it may
be the same issue.  The closing/deleting of shared XmlContainer
and XmlManager objects in Java will ignore reference counting,
and destroy the underlying native objects.

There are a couple of ways to manage this.  First,
you really must simply share the XmlManager instance,
and make sure that does not go away.
Second, you can safely share the same XmlContainer
object among threads as long as you make sure it
doesn't get deleted or closed while a thread is active.

You can also safely construct multiple XmlContainer objects
by calling XmlManager.openContainer() on the same
container name.  Multiple open calls will return multiple references
to the *same* underlying XmlContainer object in C++.
HOWEVER, when destroying those objects, be sure to
call XmlContainer.delete() and NOT XmlContainer.close().
The close() method will ignore reference counting.

In general, the close() methods on XmlManager and XmlContainer
should be avoided.  The delete() methods do what you want
most of the time.

Regards,

George

> George Feinberg wrote:
>
>> You should share a single XmlManager and open XmlContainer
>> object among threads, and only close when the application is
>> exiting.
>>
>
> Hi George,
> I rewrote the Testcase so that all Threads are using the same
> XMLManager and XMLContainer objects
> (see ftp://ftp.suse.com/pub/people/freitag/dbxml/ 
> MultithreadingTestCase.java).
> The db is now created inline.
> Unfortunately the error still happens in
> [libdbxml_java-2.1.so+0x23ae0a]  
> Java_com_sleepycat_dbxml_dbxml_1javaJNI_XmlResults_1next_1_1SWIG_10 
> +0xb0 .
>


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