Recommendation for RecyclerPool when using Java 21 Virtual Threads

[Marlon Patrick]

Hi everyone, I would like to ask for help on the best alternative to RecyclerPool for use with Java 21 Virtual Threads.

From what I've researched, there have already been two attempts to change the default pool:
- newLockFreePool: permanently aborted and deprecated
- newConcurrentDequePool: apparently postponed to 3.0

Regarding newConcurrentDequePool, in the issue https://github.com/FasterXML/jackson-core/issues/1266 the following comment was made: ThreadLocal-based pool still performs best for pre-Loom threading.

In this case, I would really appreciate it if you could clarify some doubts: 

1. What about an application using virtual threads? Did you notice any problems with newConcurrentDequePool() when used in conjunction with virtual threads?
2. In the 3.0 release, you think the default will be newConcurrentDequePool() or you are considering another alternative?
3. For Jackson 2.17.x, is newConcurrentDequePool() the recomended approach with virtual threads?

[Tatu Saloranta]

On Mon, Sep 9, 2024 at 1:25 PM Marlon Patrick <marlonp...@gmail.com> wrote:
>
> Hi everyone, I would like to ask for help on the best alternative to RecyclerPool for use with Java 21 Virtual Threads.

Hi! I am not the best person to answer but since others haven't yet
shared their knowledge I'll try to comment.

>
> From what I've researched, there have already been two attempts to change the default pool:
> - newLockFreePool: permanently aborted and deprecated

Correct: it turned out to have nasty asymmetric behavior in some
cases, essentially growing unbounded (reuse
failing but adding/returning to pool succeeding) causing OOMEs.
Reproducible with some tests.
This was bizarre and very unfortunate; implementation was simple and
seemed good.

> - newConcurrentDequePool: apparently postponed to 3.0

Correct: due to lack of information on behavior on regular threads it
seems best to require explicit configuration
by virtual thread users.

> Regarding newConcurrentDequePool, in the issue https://github.com/FasterXML/jackson-core/issues/1266 the following comment was made: ThreadLocal-based pool still performs best for pre-Loom threading.
>
> In this case, I would really appreciate it if you could clarify some doubts:
>
> What about an application using virtual threads? Did you notice any problems with newConcurrentDequePool() when used in conjunction with virtual threads?
> In the 3.0 release, you think the default will be newConcurrentDequePool() or you are considering another alternative?

My hope is that this implementation, or something yet to add, would
take over ThreadLocal-based pool.

> For Jackson 2.17.x, is newConcurrentDequePool() the recomended approach with virtual threads?

At this point that is the assumption but I have not heard much
feedback from anyone on actual real-world
usage, unfortunately.

-+ Tatu +-

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[Joo Hyuk Kim (Vince)]

This may be out of scope, but it would be best we eventually get real-world usage and user guidance on usage with both virtual-thread and reactor.

[Tatu Saloranta]

On Thu, Sep 12, 2024 at 4:36 PM Joo Hyuk Kim (Vince)
<bean...@gmail.com> wrote:
>
> This may be out of scope, but it would be best we eventually get real-world usage and user guidance on usage with both virtual-thread and reactor.

Yes. Question is who could and would be able to provide it. I think
Quarkus project members have done work in this area, but who else?
I don't have current projects where I would be able to measure this aspect.

So this is an area where we heavily rely on community.

-+ Tatu +-

> To view this discussion on the web visit https://groups.google.com/d/msgid/jackson-user/8eca894f-e8ce-42ed-a619-0ce7f772fbfen%40googlegroups.com.