Port of: https://github.com/openjdk/panama-foreign/pull/898
Original PR body: > > This patch addresses some issues with `MemorySegment.Scope::equals`. More > specifically, when two segments are created from the same array/buffer, their > underlying scope should be equal, but currently it is not, which is confusing. > > This patch addesses that by adding a new subclass of `GlobalSession` > (`HeapSession`) whose `equals`/`hashcode` methods are defined in terms of the > heap reference it wraps. Note that the reference is deduped on construction - > that is, we always try to find the "bottom" refrence that we should try to > keep alive with the session, and we use that for comparisons (which avoid > issues when comparing buffer slices and views). > > As part of the changes, this patch also adds more javadoc on > `MemorySegment.Scope` to document how equality works. And, this patch also > makes all zero-length memory segments associate with the same "native" scope. > This is a scope that is always alive, but is not the global scope (not to > confuse with segments created by the global arena). While what the > implementation does today is technically correct (a new fresh scope is > returned with each new ZLMS), it seems also overkill given that the scope > associated with segments originated outside Java code is not very interesting > - if users really care about lifetime of such segments they should override > the scope with `MemorySegment::reinterpret`. This leads to some changes in > the javadoc of other methods where I replaced `fresh scope that is always > alive` with just `scope that is always alive`, to avoid suggesting that a new > scope should be created each time. ------------- Commit messages: - add M's javadoc rrefinements - 8317050: Scope should reflect lifetime of underying resource Changes: https://git.openjdk.org/jdk/pull/16126/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16126&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8317819 Stats: 268 lines in 12 files changed: 210 ins; 13 del; 45 mod Patch: https://git.openjdk.org/jdk/pull/16126.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/16126/head:pull/16126 PR: https://git.openjdk.org/jdk/pull/16126
