On 28/03/2019 8:19 pm, Michael Rasmussen wrote:
It was my assumption that the reason adding private methods were allowed with
redefineClass was to support adding/removing lambdas from method bodies, since
javac converts those into private methods.
IIUC it predates that and was added to support redefinition of native
methods.
Removing this capability would remove this support. I would assume that would
cause users a lot of headache, since from a user's point-of-view, they are just
changing the method body, which should be supported!
It will depend on how the user is generating the modified classfile
bytes for the redefinition. And we certainly want to hear about such cases.
David
-----
/Michael
From: serviceability-dev <[email protected]> on behalf of
David Holmes <[email protected]>
Sent: 28 March 2019 12:10
To: Thomas Stüfe
Cc: [email protected]; Coleen Phillimore
Subject: Re: RFC (csr): 8221528: Introduce compatibility mode with VM option
-XX:AllowRedefinitionToAddOrDeleteMethods
On 28/03/2019 4:55 pm, Thomas Stüfe wrote:
On Thu, Mar 28, 2019 at 8:40 AM David Holmes <[email protected]
<mailto:[email protected]>> wrote:
Hi Thomas,
On 28/03/2019 5:02 pm, Thomas Stüfe wrote:
> Hi Serguei,
>
> This is planned to be introduced in jdk 13?
>
> The only concern I have is that both paths (old and new behavior)
should
> be well tested, and hiding the old behavior behind an optional
switch
> may reduce its test coverage considerably.
The old behaviour is hardly ever used - I'm not even sure we currently
have a test that tries to use it - so it's already not "well tested"
and
there's no intent here of increasing test coverage for the code we plan
to remove. The new path will be tested as we do have a test that
expects
to get the error. And Serguei will of course have a simple test that
checks the flag with both values.
I remember at least one case causing crashes in our code base where the
method ordering array was not reordered on RedefineClasses. May have
been this one: JDK-8149743.
My point is, I have seen crashes in the field coming from bytecode
agents redefining classes with method added or substracted, so it is no
theoretical problem.
My point is that we don't really care if the code works well or not,
we're intending to kill it off not improve it. It's a capability that
really should never have snuck in to the code.
Cheers,
David
Cheers Thomas
Cheers,
David
> Cheers, Thomas
>
> (p.s. html format does not work well with the OpenJDK mailing list
> archive, see
>
https://mail.openjdk.java.net/pipermail/serviceability-dev/2019-March/027612.html)
>
> On Thu, Mar 28, 2019 at 1:57 AM [email protected]
<mailto:[email protected]>
> <mailto:[email protected]
<mailto:[email protected]>> <[email protected]
<mailto:[email protected]>
> <mailto:[email protected]
<mailto:[email protected]>>> wrote:
>
> Hi All,
>
> This is request for comments and potentially reviews for the
> following CSR:
> https://bugs.openjdk.java.net/browse/JDK-8221528
>
>
> *Problem*
>
> Now, the implementation of JVMTI RedefineClasses and
> RetransformClasses allows to
> add/delete private static and private final instance methods
in the
> new class versions.
>
> It means that current implementation does not follow the JVM
TI spec
> which explicitly states:
>
> "The redefinition must not add, remove or rename fields or
methods,
> change the signatures
> of methods, change modifiers, or change inheritance."
>
> For details, please, see the spec:
>
>
https://docs.oracle.com/en/java/javase/12/docs/specs/jvmti.html#RedefineClasses
>
https://docs.oracle.com/en/java/javase/12/docs/specs/jvmti.html#RetransformClasses
>
> The decision was made to align the implementation with the spec.
> For reference, please, see the
> https://bugs.openjdk.java.net/browse/JDK-8192936.
>
> This decision is going to cause some inconveniences to the
customers.
>
>
> *Solution*
>
> The solution is to introduce a compatibility mode with new
> command-line VM option:
> -XX:{+|-}AllowRedefinitionToAddOrDeleteMethods
>
> New option will enable old behavior and allow the JVM TI
> RedefineClasses and RetransformClasses
> to add/delete private static and private final instance
methods in
> the new class versions.
> Without this option the old behavior will be disabled.
>
> New option is deprecated right away.
> The plan is to keep it for a couple of releases to allow
customers
> (tool vendors)
> to remove dependency on old behavior from their tools.
>
> Thanks,
> Serguei
>
