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$2.invokeFinalize(Ljava/lang/Object;)V+1
java.base@21.0.6
j
java.lang.ref.Finalizer.runFinalizer(Ljdk/internal/access/JavaLangAccess;)V+115
java.base@21.0.6
j java.lang.ref.Finalizer$FinalizerThread.run()V+29 java.base@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.
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