[mapserver] Java VM Crashes using the Mapscript API

Tue Jun 28 06:11:47 PDT 2005

Hallo Umberto and Christian

Christian reported a crash in layerObj.delete() which I
also detected. 
I think I understood the following:

Let's say, we have an initialized  mapObj mO;

layerObj lO = new layerObj(mO);
// Say lO is the 5th layer now.
// Now lO.swigCMemOwn == true and
//     lO.swigCPtr points onto the mO.swigCPtr->layers[4]

...
// now the mapObj is deleted but the Java-layerObj continues to live.
// the C-layer-Object mO.swigCPtr->layers[4] will deleted and freed also!
mO.delete()
// From now on O.swigCPtr points into invalid piece of C-memory.
...

Later on the Java-garbage-collector finalizes the layerObj. 

Because of "lO.swigCMemOwn == true" and "lO.swigCPtr!=0" the 
finalize-method calls 
layerObj.delete(). This method frees lO.swigCPtr which is invalid memory.

Same story about layerObj/classObj. 

Benedikt Rothe

UMN MapServer Users List <MAPSERVER-USERS at LISTS.UMN.EDU> schrieb am 
28.06.2005 12:16:01:

> 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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