[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

Malloc / free actually use internally some good optimized algorithms.

(I briefly checked implementation of malloc and it sometimes uses arenas to allocate memory, I think that zeroing can happen due to system allocating zeroed page).

However, AFIK, malloc / free have a tendency to fragmentize memory, and generally C guys avoids it due to fragmentization of memory.

>From all the checks, I noticed that CAS during spin lock is the biggest bottleneck, but I have no idea how to remove it.

Today evening I'll check how malloc works maybe I'll have some idea.

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