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

It is kind of difficult to test it, because it all depend on special Thread execution order.
I can't think of the test case temporarily.


Let my opinion simpler.


http://hg.openjdk.java.net/jdk/jdk15/file/d2c6eb3b2c8d/src/java.base/share/classes/java/util/concurrent/CompletableFuture.java#l615


In JDK15, CompletableFuture.UniApply#tryFire(), I think 
it should be like this:


    @SuppressWarnings("serial")
    static final class UniApply<T,V> extends UniCompletion<T,V> {
        Function<? super T,? extends V> fn;
        UniApply(Executor executor, CompletableFuture<V> dep,
                 CompletableFuture<T> src,
                 Function<? super T,? extends V> fn) {
            super(executor, dep, src); this.fn = fn;
        }
        final CompletableFuture<V> tryFire(int mode) {
            CompletableFuture<V> d; CompletableFuture<T> a;
            Object r; Throwable x; Function<? super T,? extends V> f;
            if ((a = src) == null || (r = a.result) == null
                || (d = dep) == null || (f = fn) == null)
                return null;
            tryComplete: if (d.result == null) {
                if (r instanceof AltResult) {
                    if ((x = ((AltResult)r).ex) != null) {
                        if (!claim())         //before completeThrowable, it should be claimed (this two lines is added by me)
                            return null;
                        d.completeThrowable(x, r);
                        break tryComplete;
                    }
                    r = null;
                }
                try {
                    if (mode <= 0 && !claim())
                        return null;
                    else {
                        @SuppressWarnings("unchecked") T t = (T) r;
                        d.completeValue(f.apply(t));
                    }
                } catch (Throwable ex) {
                    d.completeThrowable(ex);
                }
            }
            src = null; dep = null; fn = null;
            return d.postFire(a, mode);
        }
    }


before completeThrowable, it should be claimed just like following code.
This is mean to avoid two diffrent threads can invoke tryFire on same Object,
and to avoid it will both do the d.completeThrowable(x, r) successfully and do
d.postFire(a, mode) both.


Or you can tell me, Why not need to claim() before d.completeThrowable(x, r).
I suppose it is necessary.

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