[foreign-jextract] RFR: MemorySegmentPool + Allocator [v5]

[Radoslaw Smogura]

On Tue, 20 Apr 2021 07:04:47 GMT, Radoslaw Smogura <github.com+7535718+rsmogura at openjdk.org> wrote:

>> (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:
> 
>   Fix tests (!)
>   Make entries closable, to make API easier to use, and avoid searching for target queue.
>   Replace atomics is var handles

I did more optimizations and now results are 34 ns / op close to arena allocator

Interesting is that biggest gain was due to this change, performance and in generated code
//    while ((int) LOCK.compareAndExchange(this, 0, 1) != 1) { }
    while (!LOCK.compareAndSet(this, 0, 1)) { }

I thought both should give sameresults

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

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