Re: RFR: 8287809: Revisit implementation of memory session [v2]
> This is a cleanup of the memory session implementation. The main new concept > is that `MemorySessionImpl` is split into two parts: there is an > implementation of memory session and then there is a state abstraction > (`MemorySessionImpl.State`). This allows to share the state across multiple > session views, in a more clean way. The big consequence of this change is > that the routines on `ScopedMemoryAccess` now have to be defined in terms of > the state abstraction (but the changes are mostly mechanical). > > I have consolidated the implementation quite a bit, by removing all the > duplicated logic for issuing similar-looking exceptions. I have also > addressed an issue with `checkValidState` throwing a _new_ > `WrongThreadException` instead of using a singleton (which is what the logic > for closing down shared session requires, to avoid stack walks that are too > deep). > > `MemorySession.State::checkValidState` is now fully monomorphic; when looking > at benchmarks, this seems to be the best solution in order to make things > fast. Specializing implmentations to remove few plain checks does not buy > enough, and always has the risk of adding profile pollution. Maurizio Cimadamore has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 14 commits: - Merge branch 'master' into cleanup_memory_session_impl_state - Add null check on Buffer::checkState - Add docs Simplify liveness check in Buffer Drop redundant import in DirectBuffer - Simplify checkValidState - Add fastpath for implicit session state - Merge branch 'master' into cleanup_memory_session_impl_keep_list - Fix asNonCloseable to return self Improve direct buffer code with isImplicit predicate - Drop MemorySession interface type from AbstractMemorySessionImpl - Simplify code by removing intermediate getUnsafeBase/getUnsafeOffset methods - Simplify readOnly check - ... and 4 more: https://git.openjdk.java.net/jdk/compare/8d28734e...5b8f7246 - Changes: https://git.openjdk.java.net/jdk/pull/9017/files Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=9017&range=01 Stats: 1752 lines in 39 files changed: 407 ins; 525 del; 820 mod Patch: https://git.openjdk.java.net/jdk/pull/9017.diff Fetch: git fetch https://git.openjdk.java.net/jdk pull/9017/head:pull/9017 PR: https://git.openjdk.java.net/jdk/pull/9017
Re: RFR: 8287809: Revisit implementation of memory session
On Fri, 3 Jun 2022 15:47:21 GMT, Maurizio Cimadamore wrote: > This is a cleanup of the memory session implementation. The main new concept > is that `MemorySessionImpl` is split into two parts: there is an > implementation of memory session and then there is a state abstraction > (`MemorySessionImpl.State`). This allows to share the state across multiple > session views, in a more clean way. The big consequence of this change is > that the routines on `ScopedMemoryAccess` now have to be defined in terms of > the state abstraction (but the changes are mostly mechanical). > > I have consolidated the implementation quite a bit, by removing all the > duplicated logic for issuing similar-looking exceptions. I have also > addressed an issue with `checkValidState` throwing a _new_ > `WrongThreadException` instead of using a singleton (which is what the logic > for closing down shared session requires, to avoid stack walks that are too > deep). > > `MemorySession.State::checkValidState` is now fully monomorphic; when looking > at benchmarks, this seems to be the best solution in order to make things > fast. Specializing implmentations to remove few plain checks does not buy > enough, and always has the risk of adding profile pollution. Note: other cleanups are possible - such as flattening `ResourceList` into `MemorySession.State`. While that is possible, that's a tricky step, given that the session state can be registered against a cleaner. One option, which I explored, would be to use `MemorySessionImpl` for reachability - which then has an impact on `ScopedMemoryAccess`, as we would have to add reachability fences on the session, as well as on the session state. In any case, I'd like to proceed by steps, since this cleanup was already getting big enough. - PR: https://git.openjdk.java.net/jdk/pull/9017
RFR: 8287809: Revisit implementation of memory session
This is a cleanup of the memory session implementation. The main new concept is that `MemorySessionImpl` is split into two parts: there is an implementation of memory session and then there is a state abstraction (`MemorySessionImpl.State`). This allows to share the state across multiple session views, in a more clean way. The big consequence of this change is that the routines on `ScopedMemoryAccess` now have to be defined in terms of the state abstraction (but the changes are mostly mechanical). I have consolidated the implementation quite a bit, by removing all the duplicated logic for issuing similar-looking exceptions. I have also addressed an issue with `checkValidState` throwing a _new_ `WrongThreadException` instead of using a singleton (which is what the logic for closing down shared session requires, to avoid stack walks that are too deep). `MemorySession.State::checkValidState` is now fully monomorphic; when looking at benchmarks, this seems to be the best solution in order to make things fast. Specializing implmentations to remove few plain checks does not buy enough, and always has the risk of adding profile pollution. - Commit messages: - Add null check on Buffer::checkState - Add docs - Simplify checkValidState - Add fastpath for implicit session state - Merge branch 'master' into cleanup_memory_session_impl_keep_list - Fix asNonCloseable to return self - Drop MemorySession interface type from AbstractMemorySessionImpl - Simplify code by removing intermediate getUnsafeBase/getUnsafeOffset methods - Simplify readOnly check - Add @ForceInline in hot path from var handle access - ... and 3 more: https://git.openjdk.java.net/jdk/compare/d5b6c7bd...68028fa4 Changes: https://git.openjdk.java.net/jdk/pull/9017/files Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=9017&range=00 Issue: https://bugs.openjdk.java.net/browse/JDK-8287809 Stats: 1752 lines in 39 files changed: 407 ins; 525 del; 820 mod Patch: https://git.openjdk.java.net/jdk/pull/9017.diff Fetch: git fetch https://git.openjdk.java.net/jdk pull/9017/head:pull/9017 PR: https://git.openjdk.java.net/jdk/pull/9017
