How to explicit deallocate memory segment?

[tison]

Cross refer to the concere pull -
https://github.com/openjdk/panama-foreign/pull/509

Best,
tison.

Maurizio Cimadamore <maurizio.cimadamore at oracle.com> 于2023年10月17日周二 17:59写道：
>
>
> On 17/10/2023 00:54, tison wrote:
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> A confined/shared arena is defined to associate the same lifecycle for all memory segments it allocates - that they will be deallocated on the arena closed.
>
> But it can be normal that I want to preallocate a large arena and allocate/deallocate memory segments on this arena. In this case, what design pattern can help since there is no explicit deallocate method (I found we have one in the early release but it's absent now, why?)
>
> Best,
> tison.
>
> I think the pattern you describe is that of a memory pool. That is, some memory segment is allocated at the start of the application, and its contents are recycled by multiple clients.
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> This can be done using a custom arena, such as the one decribed here:
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> https://cr.openjdk.org/~mcimadamore/panama/why_lifetimes.html
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> Note the example:
>
> ```
> SlicingPool pool = new SlicingPool();
>
> ...
>
> try (Arena slicingArena1 = pool.acquire()) {
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>     MemorySegment segment1 = slicingArena1.allocate(100);
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> } // 'segment1' becomes invalid here
>
> ...
>
> try (Arena slicingArena2 = pool.acquire()) {
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>     MemorySegment segment2 = slicingArena2.allocate(100);
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> } // 'segment2' becomes invalid here
> ```
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> That is, clients can come and go, and they will just get a _new_ arena that is based off a slice of the original segment. This simple implementation of course only works in a single thread.
>
> There were other examples of memory pools provided in the past which also worked across multiple threads:
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> https://github.com/openjdk/panama-foreign/pulls
>
> (unfortunately this is a rather old PR, and its code has diverged from the current API, but it could be used as inspiration).
>
> Maurizio
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>