RFR: 8017513: Support for closeable streams

Paul Benedict pbenedict at apache.org
Thu Jul 11 20:22:44 UTC 2013

Paul S.'s said the "negative" of using AutoCloseable is "it is no longer
clear whether a stream should be closed or not" (6/20). That's true because
the semantics of AutoCloseable indicates you have a resource that requires

However, the choice to make MayHoldCloseableResource a sub-interface of
AutoClosable should be resisted. It's an inverted design. The Liskov
principle *says that sub-interfaces can't loosen the contracts of their
superinterface. If anything, AutoCloseable should be subclass of this new
interface, which MIGHT hold a resource that requires closing. The current
choice is just plainly backwards.

For the above reason stated, and for the fact the interface adds no new
functionality, it's superfluous. If the interface relationship can't be
inverted, then chuck it -- it does nothing anyway. At the least, keep the


On Thu, Jul 11, 2013 at 3:01 PM, Henry Jen <henry.jen at oracle.com> wrote:

> On 07/11/2013 01:13 AM, Florian Weimer wrote:
> > On 07/10/2013 11:30 PM, Henry Jen wrote:
> >
> >> A new interface, java.util.MayHoldCloseableResource, indicates an
> >> implementation may or may not hold a resource need to be closed.
> >
> > Why doesn't close() throw Exception?
> Because there is really much a developer can do on that situation. The
> API simply make it not throw a *checked* exception.
> See EG discussion on this topic,
> http://mail.openjdk.java.net/pipermail/lambda-libs-spec-experts/2013-June/002081.html
> >
> >> Annotation {@link HoldsResource} may be used to guide users/static
> >> analysis tools that a MHCR instance that definitely hold a Closeable
> >> resource.
> >
> > All this looks a bit odd to me.  I suppose the idea is that you don't
> > want to give up the last reference to a closeable resource without
> > calling close()—and not leak references which out-live the call to
> > close().  This is definitely not a property of the type of the resource,
> > so I don't see why the MayHoldCloseableResource interface is needed (or
> > can confer relevant information).  The HoldsResource annotation could be
> > useful, but based on the current documentation, it's not clear if it is
> > actually intended to express the data flow property.
> >
> I would suggest you look at EG discussion on this topic. The MHCR is
> different from AutoCloseable on the chances of holding critical resources.
> Perhaps that suggests the javadoc is not clear enough, I would like to
> know what is important and missing.
> Cheers,
> Henry


More information about the core-libs-dev mailing list