This is a nice exercise in compatible migration from finalize() to
Cleaner. The compatibility would be even better with a little tweak to
the VM. Currently VM ignores empty finalize() method(s) and does not
register the instance for finalization if it has empty finalize() (just
return bytecode). There could be a special method-level runtime
annotation, say @IgnoreFinalize that would be used to annotate no-empty
finalize() methods and would have the same effect as empty method on the
VM behavior. XXXStream could then just annotate the finalize() and leave
it as is so that potential overriders of finalize() could call super.
Current approach (with AltFinalizer) is an approximation since it can
only call finalize() and close() in succession. If overridden finalize()
callse super.finalize() in the middle of the method, it may expect the
stream to be already closed for the rest of the method:
@Override
protected finalize() {
...
... pre-close logic
...
super.finalize();
...
... post-close logic (may expect stream to be already closed)
...
}
...bust since super.close() is empty, the stream is not closed yet and
will be closed by AltFinalizer after this.finalize() returns.
I don't know what impact does such order have on the compatibility.
Probably not big.
Regards, Peter
On 12/04/2017 02:25 PM, Peter Levart wrote:
Hi Rogger,
On 12/04/2017 02:17 PM, Peter Levart wrote:
Hi Rogger,
Interesting approach. Conditional finalization. You use finalization
to support cases where user overrides finalize() and/or close() and
Cleaner when he doesn't.
I wonder if it is the right thing to use AltFinalizer when user
overrides finalize() method. In that case the method is probably not
empty and calls super.finalize() (if it is empty or doesn't call
super, user probably doesn't want the finalization to close the
stream) and so normal finalization applies. If you register
AltFinalizer for such case, close() will be called twice.
Ah, scrap that. I forgot that XXXStream.finalize() is now empty, so
user overriding it and calling super does not in fact close the
stream. You have to register AltFinalizer in that case. But now I
wonder if the logic should still be 3-state and do the following:
- if user overrides finalize() - use AltFinalizer to call both: first
finalize() and then close(); else
- if user overrides close() - use AltFinalizer to call close(); else
- use Cleaner
What do you think?
Regards, Peter
