[mapserver] Java VM Crashes using the Mapscript API

Christian Schroeder mailings at ABIWOOD99.DE
Tue Jun 28 06:16:01 EDT 2005 

Hello Umberto,

Umberto Nicoletti wrote:

>Hi Christian,
>I do not think the error you are getting is due to threading issues,
>but trying what Mario suggests will at least narrow the search field.
>
>In case you are still getting errors even with synchronized code
>blocks I have a few questions for you to help me understand your
>setup:
>Do you always get errors in delete_classObj or do the segfaults happen
>in different functions?
>  
>
Yes, the segfaults alway happen in the delete_classObj function.

>If the segfault is always caused by
>delete_ClassObj then I suppose you are creating class objects in your
>java code. Is that true?
>  
>
Yes, that's true, I need to create classObjects.

>If that is the case then we can setup a very simple test to reproduce
>the problem: modify one of the examples so that it will load a map and
>then start adding classes in similar fashion to your code, but in a
>tight loop. Classes should be made eligible for gc by dropping all
>references to them. As soon as gc kicks in the vm should crash. At
>that point it will be clear that the problem is in delete_ClassObj and
>the hunting season will be open.
>  
>
I have tested a proposed solution by Benedikt Rothe yet, which said that 
one should call the delete method of the classObject after it is not 
needed any more.
This confirms my assumption that this problem occours when java's 
garbage-collector destroys the null-referenced objects. Now it seems to 
work properly.

The mapserver version we actually use is 4.4.1, we have tested 4.4.2, 
4.2.4 and 4.6.0, too before.

Thank you all for your help!

Best Regards,
Christian :-)


>BTW can you report the mapserver version you are using (I have 4.4.2
>and I know it works, so if you can use that).
>
>Best Regards,
>Umberto
>
>On 6/21/05, Christian Schroeder <mailings at abiwood99.de> wrote:
>  
>
>>Hello Umberto,
>>
>>thank your for your immediate answer.
>>I do not call the delete_ methody directly and don't think I am using
>>special gc parameters.
>>
>>And... I have read the README file before compiling the mapserver :-)
>>
>>I will try to get it to work with "synchronized"-flags als Mario Basa
>>supposed.
>>
>>Thank you!
>>
>>Christian
>>
>>
>>Umberto Nicoletti schrieb:
>>
>>    
>>
>>>Christian,
>>>are you calling the delete_ methods directly in your code or are you
>>>using some special gc paramaters?
>>>
>>>As a side note the --use-threads option to configure is *absolutely*
>>>necessary, as are brakes on your car. I think we should write it in
>>>the README (as if someone actually cared to read it :-( ).
>>>
>>>Best regards,
>>>Umberto
>>>
>>>
>>>On 6/21/05, Sean Gillies <sgillies at frii.com> wrote:
>>>
>>>
>>>      
>>>
>>>>I'm forwarding this to the users list. Hopefully, Umberto will be able
>>>>to provide some insight.
>>>>
>>>>cheers,
>>>>Sean
>>>>
>>>>On Jun 16, 2005, at 5:08 PM, Christian Schröder wrote:
>>>>
>>>>
>>>>
>>>>        
>>>>
>>>>>Dear Mr. Gillies,
>>>>>
>>>>>some weeks ago me and Florian Pepping contacted you because we had
>>>>>problems using the Java Mapscript API. Thanks to you we could solve
>>>>>these problems :-)
>>>>>
>>>>>Now we got our program doing what it's supposed to do but there is
>>>>>still a big problem left which we were not able to solve yet:
>>>>>We created a simple servlet which is created inside a Tomcat 5.0
>>>>>Webserver. This servlet created a map image (png/jpg) and displays
>>>>>some specified objects on the map. (We use it for location based
>>>>>services --> "show me the position of the next printer").
>>>>>After an irregular number of calls of our servlet which uses the Java
>>>>>Mapscript API the complete Java VM and with it the Tomcat crashes. I
>>>>>attached the error report below. The program works properly for a
>>>>>number of calls (between 5 and 1000 :-) ) and after that it crashes.
>>>>>We have tried several versions of the mapserver (4.4.1, 4.4.2, 4.2.4,
>>>>>4.6.1 RC1) and compiled the Java Mapscript Module with JDK 1.4.2 and
>>>>>1.5.0. We also configured mapserver using the --with-threads option,
>>>>>but all this did not help. By the way the mapserv cgi-module works
>>>>>properly.
>>>>>
>>>>>Do you have an idea for this?
>>>>>
>>>>>Thanks for your anxiety
>>>>>
>>>>>Christian & Florian
>>>>>University of Paderborn, Germany
>>>>>
>>>>>
>>>>>-------------------------------------------------------------------
>>>>>
>>>>>JavaMapscriptLoader: mapscript native library has been loaded.
>>>>>* mapscript native library loaded *
>>>>>
>>>>>An unexpected exception has been detected in native code outside the
>>>>>VM.
>>>>>Unexpected Signal : 11 occurred at PC=0x3338268
>>>>>Function=delete_classObj+0x8
>>>>>Library=/usr/lib/libmapscript.so
>>>>>
>>>>>Current Java thread:
>>>>>       at edu.umn.gis.mapscript.mapscriptJNI.delete_classObj(Native
>>>>>Method)
>>>>>       at edu.umn.gis.mapscript.classObj.delete(classObj.java:32)
>>>>>       at edu.umn.gis.mapscript.classObj.finalize(classObj.java:26)
>>>>>       at java.lang.ref.Finalizer.invokeFinalizeMethod(Native Method)
>>>>>       at java.lang.ref.Finalizer.runFinalizer(Finalizer.java:83)
>>>>>       at java.lang.ref.Finalizer.access$100(Finalizer.java:14)
>>>>>       at
>>>>>java.lang.ref.Finalizer$FinalizerThread.run(Finalizer.java:160)
>>>>>
>>>>>Dynamic libraries:
>>>>>Can not get information for pid = 10558
>>>>>
>>>>>Heap at VM Abort:
>>>>>Heap
>>>>>def new generation   total 1152K, used 135K [0x08ae0000, 0x08c20000,
>>>>>0x08fc0000)
>>>>> eden space 1024K,   0% used [0x08ae0000, 0x08ae4078, 0x08be0000)
>>>>> from space 128K, 100% used [0x08c00000, 0x08c20000, 0x08c20000)
>>>>> to   space 128K,   0% used [0x08be0000, 0x08be0000, 0x08c00000)
>>>>>tenured generation   total 15048K, used 13624K [0x08fc0000,
>>>>>0x09e72000,
>>>>>0x0cae0000)
>>>>>  the space 15048K,  90% used [0x08fc0000, 0x09d0e1c0, 0x09d0e200,
>>>>>0x09e72000)
>>>>>compacting perm gen  total 18432K, used 18373K [0x0cae0000,
>>>>>0x0dce0000,
>>>>>0x10ae0000)
>>>>>  the space 18432K,  99% used [0x0cae0000, 0x0dcd1618, 0x0dcd1800,
>>>>>0x0dce0000)
>>>>>
>>>>>Local Time = Tue Jun 14 15:32:19 2005
>>>>>Elapsed Time = 246
>>>>>#
>>>>># The exception above was detected in native code outside the VM
>>>>>#
>>>>># Java VM: Java HotSpot(TM) Client VM (1.4.2_08-b03 mixed mode)
>>>>>#
>>>>># An error report file has been saved as /tmp/hs_err_pid10558.log.
>>>>># Please refer to the file for further information.
>>>>>#
>>>>>
>>>>>-------------------------------------------------------------------
>>>>>
>>>>>On Mar 22, 2005, at 12:02 PM, Florian Pepping wrote:
>>>>>
>>>>>
>>>>>
>>>>>          
>>>>>
>>>>>>Dear Mr. Gillies,
>>>>>>
>>>>>>I'm a student of the University of Paderborn in Germany and member of
>>>>>>the project group "Location Based Services for Wireless Devices". In
>>>>>>this project we try to position laptops and other WLAN-enabled
>>>>>>devices  using the signal strength of the WLAN. According to their
>>>>>>position, we  want to offer location based services to the persons
>>>>>>using the devices  (where I am; where's the next printer; is there a
>>>>>>friend nearby)
>>>>>>
>>>>>>In order to do this, we want to use your mapserver and the Java
>>>>>>Mapscript API to generate maps according to the actual position and
>>>>>>situation. We like to customize the map of our building and add
>>>>>>points, lines and so on.
>>>>>>
>>>>>>We have been able to compile the whole mapserver and the Java
>>>>>>Mapscript API. A small Java example also works, which presents an
>>>>>>unchanged map of our building.
>>>>>>
>>>>>>[...]
>>>>>>
>>>>>>
>>>>>>            
>>>>>>
>>>
>>>
>>>      
>>>
>
>
>  
>

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