RFR: cleanup - removed unneeded casts in jdi

Tue Jan 2 06:41:04 UTC 2018

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 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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