JEP 411: Deprecation with removal would break most existing Java libraries

[Sean Mullan]

On 6/14/21 7:34 AM, Rafael Winterhalter wrote:
> Why not add the property once this is the case, though? As it is now, I
> read the 'forRemoval' property to indicate a problem that should be
> instantly addressed. With Java 8 being a common baseline for libraries and
> the version being supported until (at least) 2030, I don't see how this
> removal would have a low impact within the next decade, if ever. Shouldn't
> the property be set if the removal is within reach? To some degree, I would
> expect that any deprecated API could be removed once it is no longer used.
 >
> As it is now, library maintainers face the choice of breaking their support
> for current users that are on Java 8/11 and rely on the security manager,
> or to remove their support to accommodate a Java release that might be many
> years in the future. For my part, supporting the security manager seems to
> be the right choice as things stand today. Over the years, I would expect
> that fewer and fewer people rely on the security manager, where this
> balance might shift. I would hope that the 'forRemoval' property would
> serve as an indicator at that time to tell library maintainers that usage
> of the security manager has decreased so much that it is time to remove the
> library support, too. I see the reason for a strong signal, deprecation
> already is such a signal, but if you give the full blow today, it is no
> longer available in the future where it might be more relevant to give.

As Alan and others have mentioned, there is no immediate plan to remove 
the APIs that SM-enabled libraries are typically dependent on, i.e., 
AccessController.doPrivileged and System.getSecurityManager. The APIs, 
when degraded will behave as if the Security Manager was not enabled. It 
isn't clear to me why that plan would have a high compatibility impact 
for libraries.

And in JDK 17, the Security Manager will still be fully supported.

The 'forRemoval' property means that the API is earmarked for removal in 
a future release. This is important, as it provides a clear warning bell 
to those that are dependent on it that it will eventually be going away.

On the other hand, if an API is only deprecated, there is no intention 
to remove it. Users usually can still expect the API to continue to work 
as specified. It isn't as strong enough of a signal that it should not 
be used and in my opinion would only delay the removal of the Security 
Manager for many more years.

I also think it would be more confusing, and possibly wrong to degrade 
or "stub" a deprecated API (one that is not marked forRemoval) such that 
it is a no-op or basically no longer works as expected.

--Sean

> 
> Am Mo., 14. Juni 2021 um 11:26 Uhr schrieb Ron Pressler <
> ron.pressler at oracle.com>:
> 
>> The JEP addresses this:
>>
>>> In future JDK releases, we will degrade the Security Manager APIs so
>> that they
>> remain in place but have limited or no functionality. ... This will allow
>> libraries
>> that support the Security Manager and were compiled against previous Java
>> releases
>> to continue to work without change or even recompilation. We expect to
>> remove the
>> APIs once the compatibility risk of doing so declines to an acceptable
>> level.
>>
>> If your question is, when only few codebases will refer to the API and the
>> compatibility impact is low enough for it to be removed, what if some of
>> those
>> few libraries still want to support versions prior to the removal, the
>> answer is
>> the same as with all removals (MR-JARs, or multiple artefacts). By
>> definition,
>> the impact of complete removal when the impact is low, would be low.
>>
>> — Ron
>>
>>> On 14 Jun 2021, at 09:38, Rafael Winterhalter <rafael.wth at gmail.com>
>> wrote:
>>>
>>> One example for a currently necessary "doPrivileged" are Java agents
>> where
>>> a class loading triggers agent code where the agent shares the stack with
>>> any code that loads a class for the first time. Otherwise, Byte Buddy
>> wraps
>>> anything that might require privileges as privileged action to allow
>>> setting a policy that gives Byte Buddy for example access to class
>> loaders,
>>> system properties or other things that the security manager currently
>>> checks. There's many uses of the security manager throughout the library,
>>> in the spirit of the API's invention.
>>>
>>> I could, of course, rip this code out of the library. But this would make
>>> it impossible for users that choose to use the functionality for now to
>>> update their dependency. This would certainly hinder a smooth transition
>> as
>>> library maintainers will always have people drag at both ends of the JDK
>>> version range. After all, Java 8 is supported for another decade.
>>> Multi-release jars are neither a feasible option. They are not globally
>>> supported by all class loaders, and would require me to add a copy of an
>>> adjusted class file for any Java version prior to the removal version or
>>> upwards from there. I don't think that this should be addressed by
>> tooling
>>> if keeping deprecated skeletons of the API can so easily avoid this
>> entire
>>> problem for all libraries without the need to chase down maintainers.
>>>
>>> Therefore, I really think that the SecurityManager and AccessController
>>> APIs should remain as skeletons and be deprecated, but not be marked
>>> forRemoval, especially without a clear roadmap for the actual removal
>>> forward. And while I appreciate the clean up effort - I do think the
>>> SecurityManager deprecation and feature removal is a right decision - I
>>> find the attempt to remove this API will cause unnecessary breakage and
>>> cause thousands of libraries to become unlinkable on future VM, without a
>>> clear need for it. Discovering this breakage would also require manually
>>> scanning the content of each library and affect all the big names in the
>>> industry. This would require big waves of dependency updates, where such
>>> updates sometimes will be impossible if only a single (transitive)
>>> dependency has not catched up, including major names such as Spring,
>>> Hibernate or Mockito. From experience, such major updating waves are
>> often
>>> complex and therefore avoided, which will hinder adoption of future JVM
>>> versions. This seems like a very high price to pay which could be easily
>>> avoided by only keeping a handful of skeleton classes.
>>>
>>> Am Mo., 14. Juni 2021 um 07:55 Uhr schrieb Alan Bateman <
>>> Alan.Bateman at oracle.com>:
>>>
>>>> cc'ing security-dev as that is the mailing list to use for this JEP.
>>>>
>>>> This JEP is the first of several in a multi-release/multi-year effort.
>>>> It's way too early to give any guess as to when the APIs will be
>>>> removed. As the JEP says, future releases may degrade the SM APIs so
>>>> that System.getSM returns always returns null or
>>>> AccessController::doPriv just runs the action. This should mean that
>>>> libraries that are compiling to older releases should continue to
>>>> compile and run on those releases. When they run on some future release
>>>> that degrades the implementation then it will be as if there is no SM.
>>>> So I would say the impact is little to none for libraries for the
>>>> foreseeable future.
>>>>
>>>> -Alan
>>>>
>>>>
>>>> On 13/06/2021 21:28, Rafael Winterhalter wrote:
>>>>> I am currently looking into how I should address JEP 411 in my library
>>>> Byte
>>>>> Buddy and I find it rather challenging. The problem I am facing is
>> that I
>>>>> know of several users who rely on the security manager in their Java
>> 8/11
>>>>> applications. I would like to continue to support those users' use
>> cases
>>>> as
>>>>> long as I support Java versions that contain the security manager,
>> which
>>>>> will be for many years to come. At the same time, I would like to
>> address
>>>>> the announced removal of the API and make sure that Byte Buddy can work
>>>>> without it prior to the deadline when the library in its current state
>>>>> would no longer link.
>>>>>
>>>>>  From my understanding of the intention of JEP 411, the API was supposed
>>>> to
>>>>> be stubbed – similar to Android’s stubbing of the API - rather than
>> being
>>>>> removed. However, with the announced deprecation for removal of
>>>>> AccessController and SecurityManager, I understand that I would need to
>>>>> fully remove the dispatching to work with future Java versions.
>>>>>
>>>>> Furthermore, it is difficult to create a working facade for dispatching
>>>> to
>>>>> the security manager only if it is available. Methods like
>>>>> AccessController.doPrivileged are caller sensitive and by adding a
>>>> utility
>>>>> to a library, this utility would leak to any potential user. It would
>>>>> therefore require package-private dispatchers for any relevant package,
>>>>> which would lead to a lot of copy-paste to retain backwards
>> compatibility
>>>>> (given that a library cannot assume to be run as a module).
>>>>>
>>>>> Finally, removing the API would mean that Byte Buddy versions of the
>> last
>>>>> ten years would no longer link in future JDKs. For Byte Buddy where new
>>>>> Java versions often require an update, that might not be a big issue
>> but
>>>>> many other libraries do support the API, I don’t feel it would be a
>>>> rather
>>>>> severe restriction and cause unnecessary breakage if API is removed,
>>>> rather
>>>>> than stubbed. I am thinking of libraries like Netty here which are
>> rather
>>>>> omnipresent and would suddenly no longer link, a concept that is
>> unlikely
>>>>> intuitive to a lot of developers.
>>>>>
>>>>> Therefore, my question is: should SecurityManager, AccessController and
>>>> the
>>>>> Policy APIs really be deprecated for removal? Rather, I think that the
>>>> APIs
>>>>> should be deprecated, but be retained with stubbed implementations.
>>>>> System.getSecurityMananger would then always return null.
>>>>> System.setSecurityManager on the other hand could be deprecated for
>>>>> removal. This way, existing code could continue to work as if the
>>>> security
>>>>> manager is not active, which already is the common scenario and would
>> not
>>>>> cause any disruption at the small price of keeping a handful of some
>>>>> stubbed classes.
>>>>>
>>>>> Thanks for advice on how this is intended to be handled by library
>>>>> developers like me.
>>>>> Best regards, Rafael
>>>>
>>>>
>>
>>