RFR: 8323807: Async UL: Add a stalling mode to async UL

[Johan Sjölen]

On Tue, 17 Dec 2024 10:52:27 GMT, Afshin Zafari <azafari at openjdk.org> wrote:

> Nice work, but I did not understand the role of stalled message in this producer-consumer pattern. Why this pseudo-code is not suitable here?
> 
> ```
> void produce() {
>   OuterLock olock;
>   InnerLock ilock;
>   while (attempt_produce(shared_buffer)){
>     ilock.wait();
>   }
> }
> 
> void consume() {
>   InnerLock ilock;
>   consume(shared_buffer); // and/or flush the whole buffer
>   ilock.notify();
> }
> ```
> 
> Since when consumer notifies producers via the `ilock`, there is free space in the buffer (since it is flushed) and the producer(s) can try again to put their messages.

Good question, the reason is slightly obscure. I wanted to guarantee that larger-than-buffer messages can be logged. It's highly unlikely that such messages occur, but I thought it best to deal with that situation now instead of regretting it with an infinitely stalled thread at a user later.

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PR Comment: https://git.openjdk.org/jdk/pull/22770#issuecomment-2548219917