Scheduler API Feedback

[Alan Bateman]

On 13/10/2025 18:52, Mengyang Li wrote:
> :
>
> I came up with a new idea — what if we provide an additional Delay 
> interface?
>
> If the current scheduler implements this interface, we can use the 
> scheduler’s own delay method.
>
> Otherwise, we fall back to `DelayedTaskSchedulers.schedule`.
>
> Currently, Loom only optimizes ForkJoinPool for this case.
>
> ``` java
>
> VirtualThreadScheduler scheduler(boolean revealBuiltin) {
>     if (scheduler instanceof BuiltinDefaultScheduler builtin && 
> !revealBuiltin) {
>         return builtin.externalView();
>     } else {
>         return scheduler;
>     }
> }
>
> ```
>
> But if I use Netty’s EventLoop as the scheduler, being able to 
> implement delay based on the event loop would be fantastic.
>

For now, the experimental/prototype for custom schedulers will only call 
out to the custom scheduler to execute a task that starts or continue a 
virtual thread. The VirtualThreadScheduler interface could be extended 
to allow the custom scheduler to take on delayed tasks but these are not 
virtual thread tasks, they are tasks to support timed-Object.wait for 
timed-park. You are right that a SPTE based implementation is used in 
the JDK when there is a custom scheduler configured. Is this causing an 
issue? Timeouts are usually cancelled, >99% in many cases, so I'd like 
to understand if your workloads are different, maybe you have more 
scenarios where a timeout occurs?

-Alan
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