[gdal-dev] Java bindings to gdal/ogr - looking for more developer documentation

[Even Rouault]

Hi Tom,

please file an issue at https://github.com/OSGeo/gdal/issues with your 
reproducer snippet

Even

Le 17/07/2025 à 02:28, Tom Moore a écrit :
> Hi Evan
>
> I seem to still be having problems closing datasets in Java resulting 
> in a JVM crash, using gdal-3-13-3_x64 downloaded from the GISInternals 
> site.  Below is the stack trace information.
>
> ---------------  T H R E A D  ---------------
>
> Current thread (0x000001ffd39932c0):  JavaThread "Finalizer" daemon 
> [_thread_in_native, id=25140, 
> stack(0x000000ba6eb00000,0x000000ba6ec00000) (1024K)]
>
> Stack: [0x000000ba6eb00000,0x000000ba6ec00000], 
> sp=0x000000ba6ebfed60,  free space=1019k
> Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, 
> C=native code)
> C  [gdal.dll+0xc86927]
>
> Java frames: (J=compiled Java code, j=interpreted, Vv=VM code)
> j  org.gdal.gdal.gdalJNI.delete_Dataset(J)V+0
> j  org.gdal.gdal.Dataset.delete()V+25
> j  org.gdal.gdal.Dataset.finalize()V+1
> j  java.lang.System$2.invokeFinalize(Ljava/lang/Object;)V+1 
> java.base at 21.0.6
> j 
> java.lang.ref.Finalizer.runFinalizer(Ljdk/internal/access/JavaLangAccess;)V+115 
> java.base at 21.0.6
> j  java.lang.ref.Finalizer$FinalizerThread.run()V+29 java.base at 21.0.6
> v  ~StubRoutines::call_stub 0x000001ffa369100d
>
> siginfo: EXCEPTION_ACCESS_VIOLATION (0xc0000005), reading address 
> 0xffffffffffffffff
>
> The crash is happening when the swig delete_Dataset method, called by 
> the finalizer, calls into the gdal.dll.
>
> I tried calling Open() and Close() several times in a row to see if 
> this would trigger the problem, like this:
> gdal./AllRegister/();
>  Dataset ds = gdal.Open(filename);
>  ds.Close();
>  ds.Close();
>
> but that seemed to work ok.
>
> I also tried open and close sequences, like this:
>  Dataset ds = gdal.Open(filename);
>  ds.Close();
>  ds = gdal.Open(filename);
>  ds.Close();
>  ds = gdal.Open(filename);
>  System.gc();
>  System.runFinalization();
>
> This didn't trigger a problem either.  I did a few more tests, 
> repeating steps of opening a dataset, reading a band, closing the 
> dataset, and this didn't do it either.
>
> If I enable CPL_DEBUG then my pattern of access that causes the crash is:
> GDAL: 
> GDALDriver::Create(GTiff,c:/tmp/test1.tif,10,10,1,Int32,000001BCB9893680)
> GDAL: GDALClose(c:/tmp/test1.tif, this=000001BCB9872A90)
> GDAL: GDALOpen(c:/tmp/test1.tif, this=000001BCB98784D0) succeeds as GTiff.
> GDAL: GDALClose(c:/tmp/test1.tif, this=000001BCB98784D0)
> GDAL: GDALOpen(c:/tmp/test1.tif, this=000001BCBE486550) succeeds as GTiff.
> GDAL: GDALOpen(c:/tmp/test1.tif.vat.dbf, this=000001BCBE10D070) 
> succeeds as ESRI Shapefile.
> GDAL: GDALClose(c:/tmp/test1.tif.vat.dbf, this=000001BCBE10D070)
> GDAL: GDALClose(c:/tmp/test1.tif, this=000001BCBE486550)
>
> Around this point the finalizer kicks in and the JVM crashes.
>
> This is a hard one for me to track down, because I don't know the 
> tooling to debug native cpp code from within Java.  What I could do is 
> insert some debugging statements in to the code to try to see what is 
> going on.  If you have any suggestions about this I would be happy to 
> try it.
>
> Tom
>
>
> On Fri, May 30, 2025, at 5:53 PM, Even Rouault wrote:
>>
>> Le 30/05/2025 à 23:39, Tom Moore a écrit :
>> > Hi Even
>> >
>> > I just wanted to update you and provide a record for posterity with
>> > the results of me playing around with gdal/java and resource 
>> management.
>> >
>> > It appears to me that Dataset objects should not be closed from Java
>> > client code.  If you do then often there will be an access violation
>> > (native null pointer) that will crash the JVM. From the dump file the
>> > following stack trace shows the Java code being executed when the
>> > exception occurs:
>>
>> I believe this issue should be fixed in 3.11.0 per
>> https://github.com/OSGeo/gdal/commit/ec4ca7930b48653bb0fac27b59c6c1bf883c45f2
>>
>> Actually historically this was the .delete() method that should be
>> called. The exposition of .Close() is quite recent and was broken (until
>> the above mentioned fix)
>>
>> >
>> > Java frames: (J=compiled Java code, j=interpreted, Vv=VM code)
>> > j  org.gdal.gdal.gdalJNI.delete_Dataset(J)V+0
>> > j  org.gdal.gdal.Dataset.delete()V+25
>> > j  org.gdal.gdal.Dataset.finalize()V+1
>> > j java.lang.System$2.invokeFinalize(Ljava/lang/Object;)V+1
>> > java.base at 21.0.6
>> > j
>> > 
>> java.lang.ref.Finalizer.runFinalizer(Ljdk/internal/access/JavaLangAccess;)V+115 
>>
>> > java.base at 21.0.6
>> > j  java.lang.ref.Finalizer$FinalizerThread.run()V+29 java.base at 21.0.6
>> >
>> > So it looks like the swig bindings implement a finalizer to dispose of
>> > the native object when the reference is no longer reachable (nice!).
>> > However it looks like there might not be any protection to prevent bad
>> > things from happening when the Delete method is called more than
>> > once.  It appears that in this case that when the finalizer calls
>> > Delete on the Dataset the jvm crashes because the Dataset has already
>> > been closed manually and the resources have already been released.
>> >
>> > If I am correct in this conclusions then this is not a problem.  If
>> > correct I suggest that either the docs be updated to indicate do not
>> > manually call Delete on the Dataset object, or change the Delete
>> > method code to gracefully handle multiple calls (better choice).
>> >
>> > By the way, something to note for the future is that finalizers have
>> > been deprecated since Java 9 (2017).  This is described in
>> > https://openjdk.org/jeps/421. Although deprecated, finalizers are
>> > still allowed in modern jdk's and probably will be for a while yet. At
>> > some future time they will be removed.  The suggested replacement for
>> > finalizers are cleaners, but they are only available in Java 9+.  When
>> > finalizers are removed there will need to be a new set of bindings
>> > that use cleaners.  You can probably ignore this problem for a few
>> > more years, but at some point you will need to provide two sets of
>> > Java bindings (one required for Java 8 and earlier, and one required
>> > for some future Java and later).
>>
>> Thanks for the heads up. Seizing the opportunity to remind interesting
>> parties in the GDAL Java bindings that they should not be shy and are
>> welcome to be proactive. On my side, they are very very minimilastically
>> maintained.
>>
>> Even
>>
>> -- 
>> http://www.spatialys.com
>> My software is free, but my time generally not.
>>
>>
>
> --
> Tom Moore
> Spatial Planning Systems
> 960 Burkes Bluff Lane
> Deep River ON  K0J 1P0
> Canada
>
> Phone: +1 613 584 9354
>
-- 
http://www.spatialys.com
My software is free, but my time generally not.
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