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

[Peter Firmstone]

On 14/06/2021 9:34 pm, 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.


I too suggested and support this approach.


> 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 this reason, I'm proposing a minimal change allowing us to implement 
Guard::check hooks at existing check points within the JVM using the 
security provider mechanism that can be back-ported and supported on all 
LTS releases, without any new Java API's.

We require authorization layer functionality, I will be implementing it, 
and it will be freely available under an AL2.0 license.

It would be nice to keep AccessController and AccessControlContext and 
use a property to enable or disable the stack walk for those who don't 
require it, however they are now marked for removal, so I'll be looking 
at using wrapper classes around them, so their implementations can be 
replaced at a later data.

Our current implementation is high scaling with minimal performance 
impact, however I can't make any promises regarding future performance, 
but hopefully it will come to be as performant as our current 
implementation.

Regards, Peter.

> 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.
>
> Am Mo., 14. Juni 2021 um 11:26 Uhr schrieb Ron Pressler 
> <ron.pressler at oracle.com <mailto: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 <mailto: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 <mailto: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
>     >>
>     >>
>
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