New methods in PriorityQueue

[Julian Waters]

Hi all,

I apologize for the confusion, it seems like something went awry on my end
with the mailing lists, since there are apparently now 2 copies of the same
thread with different names. I guess I'll just go with this one, since the
technical discussion is going on here.

To clarify, I wasn't the one who created the PR, I'll relay the feedback to
the author since I'm not really in the position to give any feedback
myself, given my inexperience with this area of the JDK.

Thank you Stuart and Roger for the replies, have a great day! :)

best regards,
Julian



On Fri, Mar 4, 2022 at 1:37 PM Stuart Marks <stuart.marks at oracle.com> wrote:

> I agree with Roger. Let me amplify this.
>
> The general rule for collections that use hashes and comparison methods
> (such as
> HashMap and TreeMap, as well as PriorityQueue) is that one mustn't mutate
> any
> element that resides in such a collection in any way that changes the
> results of
> hashCode, equals, or the comparison method. It's a bad precedent to add
> APIs that
> seem to support such mutation. As Roger said, the supported way of doing
> this is to
> remove, mutate, and then reinsert.
>
> It seems like it might be safe to mutate an element, only temporarily
> violating the
> PQ's invariants until the mutated element is sifted into the correct
> position.
> However, even a "temporary" violation is exceedingly dangerous. If some
> other
> modification is made to the PQ while it's in this state, it could end up
> permanently
> corrupting the PQ.
>
> Managing such a situation would need to be handled exceedingly carefully.
> As such,
> this seems like a highly specialized use case, thus the proposal isn't
> suitable as a
> general-purpose API.
>
> s'marks
>
>
> On 3/3/22 10:18 AM, Roger Riggs wrote:
> > Hi Julian,
> >
> > Modifying the priorities of elements in the PriorityQueue violates the
> > invariants of the PriorityQueue established at insertion and maintained
> > at removal by the Comparator.
> >
> > To maintain the invariant the element should be removed, its priority
> modified,
> > and re-inserted.
> >
> > An API to manually manipulate the order is inconsistent with the design
> of
> > PriorityQueue.
> >
> > Regards, Roger
> >
> >
> > On 3/3/22 6:59 AM, Jules W. wrote:
> >> Hi all,
> >>
> >> A new PR that adds methods to PriorityQueue was created some time ago at
> >> https://github.com/openjdk/jdk/pull/6938 but has no corresponding
> issue. As
> >> I'm not too familiar with this part of the JDK I'm querying this mailing
> >> list for anyone to properly review the PR before I create an issue for
> it
> >> in the JBS
> >>
> >> best regards,
> >> Julian Waters
> >
>