CompletableFuture (original) (raw)

Remi Forax forax at univ-mlv.fr
Thu Nov 29 08:02:42 PST 2012

On 11/29/2012 04:19 PM, Doug Lea wrote:

On 11/29/12 09:53, Remi Forax wrote:

again Future<? extends U>. Thanks.

I think that CompletableFuture<?> is better as return type than CompletableFuture otherwise users may want to declare a local variable Void. We end up using explicit Void params in FJ stuff a lot and people seem OK with it, so we might as well make these use the same conventions unless anyone can think of a reason otherwise.

j.u.c.ExecutorService use the <?> convention, see submit(Runnable), so now I let you choose if you perfer to be inconsistent with ExecutorService or FJ :)

/** * Creates and returns a CompletableFuture that is completed with * the result of the given function of either this or the other * given CompletableFuture's results if/when either complete * normally. * * @return the new CompletableFuture */ public CompletableFuture or(CompletableFuture<? extends_ _T> x, BiFunction<? super T,? super_ _T, ?_ _extends U> fn); Thinking a little more about this one, fn should be a Function not a BiFunction given that only one of the two completables needs to complete. Yes, thanks. (I fixed this before but then overwrote with old version; oops.) /** * Returns the value if completed, else the given valueIfAbsent. */ public T getNow(T valueIfAbsent); still think it should use a supplier as parameter and not the value. The motivating use case is to allow simplification of polling-like constructions where you'd otherwise need to first check isDone, and then get(), but could replace with: while(t.getNow(NOTREADY) == NOTREADY) { doSomethingElse(); } in which case trapping into a function is not at all helpful.

you mean, XXX value; while((value = t.getNow(NOTREADY)) == NOTREADY) { doSomethingElse(); }

And I can't think of other cases not involving plain get() where this method is of much use.

Ok, given that I can write getNow(supplier) from getNow(valueIfAbsent), your signature is better than mine.

public static T getNow(CompletableFuture future, Supplier<? extends T> supplier) { Object value; if ((value = future.getNow(NOT_READY) == NOT_READY) { return supplier.supply(); } return (T)value; }

-Doug

Rémi

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