[foreign-jextract] RFR: MemorySegmentPool + Allocator [v9]

[Radoslaw Smogura]

> (Preview)
> 
> The MemorySegmentPool is a pool maintaining memory segments, optionally can expose allocator which can be bound to other scope, and which will return allocated segments back to pool.
> 
> However the best results has been achieved by using getSegmentEntry & putSegmentEntry methods.
> 
> The pool is intended to be used by long running applications (i.e. like global shared pool), where fast allocation and de-allocation of segments is critical (was designed during implementation of I/O subsystem with Panama, as a pool for temporary buffers between system I/O methods and Java byte arrays from InputStreams).
> 
> The pool uses hand-made SpinLockQueue as the Deque from JDK offers too much functionality and overhead.

Radoslaw Smogura has updated the pull request incrementally with one additional commit since the last revision:

  Prevent double adding element to queue
  
  Dealt with slow write issue - had to create segment with aligned size, not
  a bit shift.
  
  ForceInline allocatorForScope and allocate method - this is outcome
  from performance tests, and probable scalarization of segment.
  
  Some changes to inlining / no inlining.

-------------

Changes:
  - all: https://git.openjdk.java.net/panama-foreign/pull/509/files
  - new: https://git.openjdk.java.net/panama-foreign/pull/509/files/cf5c2e02..536e71aa

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=509&range=08
 - incr: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=509&range=07-08

  Stats: 130 lines in 3 files changed: 111 ins; 4 del; 15 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/509.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/509/head:pull/509

PR: https://git.openjdk.java.net/panama-foreign/pull/509