In case anyone else finds this on a Google search:
Most Java objects are cleaned up through garbage collection, but some need
to be explicitly told to dispose of themselves when they are no longer
needed. The usual example is a file handle; you need to tell Java to close
that handle when you are done with it. ParcelableFileDescriptor is merely a
parcelable wrapper around a file handle, so it has this same need.
Now consider this implementation of an AIDL interface:
public ParcelableFileDescriptor doSomething(ParcelableFileDescriptor
withFile) {
someOtherRemoteAidlInterface.help(withFile);
return withFile;
}
The question is, when do you close this ParcelableFileDescriptor? When this
function returns, it still hasn't been sent back to the caller yet. However
we are certainly done with it and we want to ensure it's closed. Luckily,
the AIDL compiler uses PARCELABLE_WRITE_RETURN_VALUE and when the
ParcelableFileDescriptor sees this flag, it automatically closes itself. So
we don't have to do anything.
Any ParcelableFileDescriptor that isn't being returned has to be closed
explicitly:
public ParcelableFileDescriptor doSomething(ParcelableFileDescriptor
withFile) {
someOtherRemoteAidlInterface.help(withFile);
withFile.close();
return ParcelableFileDescriptor.open(new File("result file"),
MODE_READ_ONLY);
}
...And that's all there is to it. ParcelableFileDescriptor uses the flag to
close itself. The internal framework class InputChannel uses the flag for
the same reason. I don't believe there are any other parcelable objects
that care whether or not PARCELABLE_WRITE_RETURN_VALUE has been set.
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