Future#join then contract #transform break [Regression from 4.5.4] about vert.x HOT 7 CLOSED

the transform javadoc says: When this future (the one on which transform is called) completes, the mapper will be called with the async result and this mapper returns another future object.

It is possible to extrapolate that join returns a composite future that when it is a success is resolved with the composite future. However as soon as you call transform on this future, then the contract of transform applies.

It is specified that the mapper receives an asynchronous result and not the current future. It turns out it was practical to pass the current future in the initial implementation but this can create leak since the transform operation needs to keep a reference onto the future that created it.

Therefore if the result of join is a success then the mapper of transform is called with an asynchronous result for which the composite future can be obtained with the result of this async result, e.g transform(ar -> { ... ar.result() <- CompositeFuture ... })

from vert.x.

cc @vietj

from vert.x.

thanks

from vert.x.

@Fyro-Ing I see what you mean but this actually seems to be an abuse of the API, if you want to use the composite future. Simply keep a reference on it like

  @Test
  public void join() {
    waitFor(1);

    final Future<String> f1 = Future.failedFuture(new RuntimeException());
    final Future<String> f2 = Future.failedFuture(new RuntimeException());

    CompositeFuture cf = Future.join(f1, f2);
    cf
      .transform(ar -> {
        // Use CF
        return (CompositeFuture) ar;
      })
      .onComplete(ar -> {
        complete();
      });

    await();
  }

from vert.x.

I suppose that sample as error with ar cast vs cf

This is a breaking change, because transform use previous result, and now, this is not the case.
And now, we need a reference and can't use fluent API directly :/

from vert.x.

from vert.x.

I'm not sure how to understand your response, but ar (result from #join) is not a CompositeFuture now, this is a breaking change, from method contract ^^

from vert.x.