Hi David,
On 11/1/2017 10:30 PM, David Holmes wrote:
On 2/11/2017 5:07 AM, Stuart Marks wrote:
On 10/31/17 6:58 PM, David Holmes wrote:
I'm not sure why you say this isn't helpful. It's clearly not
helpful to *clients* of TPE; but since finalize() is protected, the
warning is clearly directed at subclasses, and it provides
information about migrating away from finalization. Should say
something different?
It isn't helpful to people subclassing TPE (or any class that
defines finalize()) because the general strategies described in
Object.finalize() can't be applied by the subclass independent of
the class (TPE here) it is subclassing. Unless TPE provides an
alternate mechanism, the subclass is stuck with finalize().
I don't understand why the subclass has to rely on the mechanism
provided by its superclass (TPE here). I'm thinking of a case like
the following.
Suppose a subclass has some independent native resource that it needs
to clean up. Prior to the introduction of java.lang.ref, the only
thing available was finalization. The subclass would have to override
finalize(), do its own cleanup, and then make sure to call
super.finalize().
With Cleaner in JDK 9, the subclass can refactor its native resources
into a Cleanable, register it with a Cleaner, and then clean up its
native resources when the Cleanable's clean() method is called.
Can't this be done independently of TPE and finalization?
Of course it can. The independent part of the subclass can use
whatever mechanism it likes - it's independent. The point is that if
the subclass needs to coordinate it's additional cleanup with the
shutdown done by finalize() then it needs a means to do so.
Given the use cases and the context in which an unreferenced resource
needs to be
released, I don't think a fully general purpose mechanism is appropriate.
If there are dependencies in the cleanup those can be references between
the dependent
objects. Those dependencies will ensure that cleanup of each occurs
when it is unreferenced.
It is more robust if each resource handles its own cleanup. Peter
already suggested
that if coordination was required, the mechanism should be explicitly
provided by the
owning/coordinating object.
Roger
David
s'marks
