[mapserver] Java VM Crashes using the Mapscript API
Umberto Nicoletti
umberto.nicoletti at GMAIL.COM
Tue Jun 28 10:15:18 EDT 2005
This is what I also suspected and this is why I never attempt to
release objects on my own, but I always leave it up to the gc.
Even in that case a segfault is indeed possible and that's why we need
to open an issue on bugzilla so that the developers know.
A patch is probably not too difficult to develop if only I had more time :-(
Regards,
Umberto
On 6/28/05, Benedikt Rothe <umn-ms at hydrotec.de> wrote:
>
> 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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