RFR: cleanup - removed unneeded casts in jdi
David Holmes
david.holmes at oracle.com
Tue Jan 2 09:17:24 UTC 2018
On 2/01/2018 6:21 PM, Langer, Christoph wrote:
> Hi David,
>
> thanks for pointing this out. I see what you mean.
>
> However, you were the one who brought up the point that rather the Location interface should specify the means to compare two Locations :)
All I meant by that is that Location should _specify_ what it means to
compare two Locations. Any interface (or class for that matter) that
implements Comparable should provide an overriding specification for
compareTo.
> And that would be an interface default method - or would there be another way? I guess, as there are no generics involved, the overloading instead of overriding thing should at least be more obvious for other implementers of the Location interface. But, for sure, I'm leaving the decision whether the default interface is the right thing here or not to better language and jdi experts than I am. Egor's original proposal should work well, too, and is definitely less obtrusive.
Yeah I'm going to punt on this one too. :)
> BTW: your suggested change in MirrorImpl to go from "protected VirtualMachineImpl vm;" to "protected VirtualMachine vm;" would not really work out as VirtualMachineImpl extends MirrorImpl and in there VirtualMachineImpl is definitely needed. It's really a bit weird...
Thanks for checking. Despite the use of interfaces and classes this
stuff doesn't really seem to be that amenable to supporting alternative
implementations of the interfaces.
Cheers,
David
> Best regards
> Christoph
>
> -----Original Message-----
> From: David Holmes [mailto:david.holmes at oracle.com]
> Sent: Dienstag, 2. Januar 2018 08:31
> To: Langer, Christoph <christoph.langer at sap.com>; Egor Ushakov <egor.ushakov at jetbrains.com>; serguei.spitsyn at oracle.com; serviceability-dev at openjdk.java.net
> Subject: Re: RFR: cleanup - removed unneeded casts in jdi
>
> Hi Christoph,
>
> On 2/01/2018 4:41 PM, Langer, Christoph wrote:
>> Hi Egor, David and Serguei,
>>
>> I had a look at this, too. I would think this really calls out for a
>> “public default int compareTo(Location other) {…}” in Location.java
>
> I think this could run into the "overloads instead of overrides" problem
> that Brian describes here:
>
> http://mail.openjdk.java.net/pipermail/core-libs-dev/2017-November/050060.html
>
> ... unsure. But this would need a CSR request any way so hopefully any
> issues with doing this would be caught there.
>
> I'm very wary of adding default methods, though this may be such a
> little used interface that it's not really an issue.
>
> Cheers,
> David
>
>> which uses the implementation out of LocationImpl.java. That way, all
>> the suggested improvements for MirrorImpl.java can be done as well. And
>> other implementers of Location, such as IntelliJ’s
>> GeneratedLocation.java, would still build and won’t be necessarily wrong
>> but could probably gradually remove their compareTo methods.
>>
>> As for checking for the same VM within Location comparison, e.g. by
>> using the equals() method, I guess this can be added. At least it should
>> not add a notable cost. But I suggest to do it with a separate change,
>> in case it turns out to be not a good idea and one needs to revert it.
>>
>> @Egor: Would you mind to create an updated Webrev with an interface
>> default method?
>>
>> Best regards
>>
>> Christoph
>>
>> *From:*serviceability-dev
>> [mailto:serviceability-dev-bounces at openjdk.java.net] *On Behalf Of *Egor
>> Ushakov
>> *Sent:* Montag, 25. Dezember 2017 12:30
>> *To:* serguei.spitsyn at oracle.com; David Holmes
>> <david.holmes at oracle.com>; serviceability-dev at openjdk.java.net
>> *Subject:* Re: RFR: cleanup - removed unneeded casts in jdi
>>
>> Thanks for your comments!
>>
>> I'll try to provide more details:
>> We have our own Location implementaion in IDEA code:
>> GeneratedLocation.java
>> <https://github.com/JetBrains/intellij-community/blob/29cdd102746d2252ef282082e7671128228489f8/java/debugger/impl/src/com/intellij/debugger/jdi/GeneratedLocation.java>
>> which is not intended to be used inside the jdi, but mostly to mock
>> Location in our own APIs like PositionManager.java
>> <https://github.com/JetBrains/intellij-community/blob/306d705e1829bd3c74afc2489bfb7ed59d686b84/java/debugger/openapi/src/com/intellij/debugger/PositionManager.java>
>> Unfortunately some implementations keep the provided Location objects
>> (both LocationImpl and ours) in collections (maybe sorted) so we have to
>> prevent cast exceptions from compareTo somehow.
>> Hope it helps.
>>
>> Egor
>>
>> On 24-Dec-17 03:32, serguei.spitsyn at oracle.com
>> <mailto:serguei.spitsyn at oracle.com> wrote:
>>
>> Hi David,
>>
>> Thank you for the explanations!
>> I've got your points.
>>
>>
>> On 12/23/17 15:32, David Holmes wrote:
>>
>> Hi Serguei,
>>
>> On 23/12/2017 6:04 PM, serguei.spitsyn at oracle.com
>> <mailto:serguei.spitsyn at oracle.com> wrote:
>>
>> Hi Egor and David,
>>
>>
>> Egor,
>>
>> The fix looks good in general.
>> I've filed bug:
>> https://bugs.openjdk.java.net/browse/JDK-8194143
>> remove unneeded casts in LocationImpl and MirrorImpl
>> classes
>>
>>
>> On 12/22/17 13:06, David Holmes wrote:
>>
>> Hi Egor,
>>
>> On 23/12/2017 1:32 AM, Egor Ushakov wrote:
>>
>> Hi all,
>>
>> could you please review and sponsor this small
>> cleanup removing unneeded casts in jdi LocationImpl
>> and MirrorImpl.
>> They were preventing creating custom Location and
>> Mirror implementations used for tests and IDEA
>> debugger impl.
>> http://cr.openjdk.java.net/~avu/egor.ushakov/cast_fix/
>>
>>
>> src/jdk.jdi/share/classes/com/sun/tools/jdi/LocationImpl.java
>>
>>
>> ! public int compareTo(Location object) {
>> - LocationImpl other = (LocationImpl)object;
>>
>> The existing code is somewhat suspect as the Location
>> interface implements Comparable but it does not specify
>> what it means to compare two Locations! That's a bug in
>> itself.
>>
>>
>> Not sure, if it is really needed as it is abstract.
>> We could say: An implementation of the Location is expected
>> to specify it.
>>
>>
>> That makes it impossible to compare different implementations of
>> the Location interface. The functionality has to be specified by
>> the interface.
>>
>>
>> We probably never needed to compare them before.
>> But such comparison can be needed for an IDE that has a deal with
>> different JDI implementations.
>>
>>
>>
>> LocationImpl has decided how to compare two
>> LocaltionImp's (but doesn't even check they are in the
>> same VirtualMachine!).
>>
>>
>> Nice catch!
>> Interesting...
>> Should comparing of locations from different mirrors be a
>> no-op?
>> Not sure if it would be right to throw a VMMismatchException
>> in such cases.
>>
>>
>> Not sure - without knowing why we need to compare Locations it's
>> hard to say.
>>
>>
>> Ok.
>>
>>
>>
>> Can we generalize that to accommodate other Location
>> implementations?Your change allows for this to happen,
>> but it will only work as expected if the other Location
>> implementations use the same comparison basis as
>> LocationImpl - which is unspecified.
>>
>>
>> It is not clear, what you mean here.
>> What are the other Location implementations?
>>
>>
>> The ones that Egor is implementing and the reason for this bug
>> report.
>>
>>
>> It is not clear to me why do they need their own Location
>> implementation.
>>
>>
>>
>> A JDI implementation normally has one base implementation of
>> the Location.
>> What would be a need to have multiple?
>>
>>
>> Egor indicated it was for use in testing and the IDEA debugger.
>> It's apparent they have their own implementation of Location,
>> but these instances have to interact with the default
>> LocationImpl implementations - else this bug report would not be
>> needed.
>>
>>
>> Will need to look at it more closely after NY.
>> I'm going to vacation in a couple of hours until the Jan 3-rd.
>> Will probably have a limited internet access there.
>>
>> I wish you, guys, happy Xmas and New Year and nice Holidays!
>>
>> Thanks,
>> Serguei
>>
>>
>>
>>
>> Cheers,
>> David
>>
>>
>> And different JDI implementations are not supposed to
>> interact with each other, are they?
>>
>>
>>
>> src/jdk.jdi/share/classes/com/sun/tools/jdi/MirrorImpl.java
>>
>> Change looks good. It would also seem that now this
>> change is made that this:
>>
>> 37 protected VirtualMachineImpl vm;
>> 38
>> 39 MirrorImpl(VirtualMachine aVm) {
>> 40 super();
>> 41
>> 42 // Yes, its a bit of a hack. But by doing
>> it this
>> 43 // way, this is the only place we have to
>> change
>> 44 // typing to substitute a new impl.
>> 45 vm = (VirtualMachineImpl)aVm;
>>
>> might reduce to:
>>
>> 37 protected VirtualMachine vm;
>> 38
>> 39 MirrorImpl(VirtualMachine aVm) {
>> 40 super();
>> 41 vm = aVm;
>>
>> if we no longer depend on it being VirtualMachineImpl
>> ... and neither do subclasses.
>>
>>
>> Good suggestion.
>>
>>
>> Thanks,
>> Serguei
>>
>>
>>
>> David
>> -----
>>
>>
>> I do not have rights to create JDK bug report
>> directly, please create it if it is needed for the
>> procedure.
>>
>> Thanks!
>>
>>
>>
>> --
>>
>> Egor Ushakov
>>
>> Software Developer
>>
>> JetBrains
>>
>> http://www.jetbrains.com
>>
>> The Drive to Develop
>>
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