Re: CompletableFuture#postComplete() can be invoked concurrently?

This code is very tricky and hard to understand.
When studying this, I would only look at latest version of the code.

If you think you've found a bug, you should try to create a repro,
preferably in jsr166 CVS.
You can see some stress tests in the tests e.g look at expensiveTests in
http://gee.cs.oswego.edu/cgi-bin/viewcvs.cgi/jsr166/src/test/tck/CompletableFutureTest.java?view=markup

On Sat, Aug 22, 2020 at 8:19 AM Liu via Concurrency-interest
<[email protected]> wrote:
>
> In CompletableFuture, when I invoke the thenApply() on a CompletableFuture Object,
> There is a subtle point in time, and it will make CompletableFuture#postComplete()
> invoked concurrently.
>
>     private <V> CompletableFuture<V> uniApplyStage(
>         Executor e, Function<? super T,? extends V> f) {
>         if (f == null) throw new NullPointerException();
>         CompletableFuture<V> d =  new CompletableFuture<V>();
>         if (e != null || !d.uniApply(this, f, null)) {
>             UniApply<T,V> c = new UniApply<T,V>(e, d, this, f);
>             push(c);
>             // at this point, this CompletableFuture Object just invoke the completeThrowable(),
>             // because the process to execute Supplier throw a exception.
>             c.tryFire(SYNC);
>         }
>         return d;
>     }
>
> The thread that invoke c.tryFire(SYNC) and the thread that iovoke completeThrowable() will invoke
> c.tryFire(NESTED) soonly in postComplete() . The important thing is the two "c"  is same Object.
>
> So the two threads can invoke c.tryFire() concurrently, and in some special
> timing, the (d = dep) == null check can't work out.
>
> 1. The thread that invoke c.tryFire(SYNC) will invoke a.postComplete() in postFire() directly.
> 2. The thread that iovoke completeThrowable() will not invoke a.postComplete() in postFire(),
>     but it will return to the postComplete().
>
> Above two sentence, the two threads will invoke postComplete() on same CompletableFuture object.
>
> I'm afraid I didn't express it clearly. If you don't understand my opinion, just tell me if
> CompletableFuture#postComplete() is designed to invoked concurrently or not?
>
> PS: above code from JDK8, and I think this problem will happen too in newest JDK, if I am right about my opinion.
>
> --------------------------------------------------------------------------------
> Regards
> Liu
> _______________________________________________
> Concurrency-interest mailing list
> [email protected]
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