STS allows to bypass any checked exceptions

[Ron Pressler]

Both are awful and the second isn’t only awful but clearly uses the API in a way the documentation warns against. The purpose of STS is for the scope to not handle subtasks individually but always as a unit. Therefore, exception and result handling should be done collectively. However, we offer a way to get individual subtasks’ results to address the specific but common case where different subtasks return different types. The ISE thrown by get means one thing: there’s a bug in your code because you’ve used the API incorrectly.

If you find your scope code interested in a particular task’s exception, you’re either doing something advanced or wrong. In fact, if you’re using STS without a policy you’re either wrong or advanced.

One decision we wanted to postpone was whether or not to force users to use a policy. If real users end up doing things similar to what you’re demonstrating — which I guess we'll find out during the preview — that may well be what we do. We wanted to keep the option of not using a policy open for the benefit of advanced users, and obviously they can use the API incorrectly (in this case — intentionally). But if regular users fall into the same trap, we may choose to enforce what is now merely a recommendation.

— Ron

> On 13 May 2023, at 17:33, Remi Forax <forax at univ-mlv.fr> wrote:
> 
> The more I think about the way STS/TaskHandle manages checked exceptions the less I like it.
> 
> Here is my problem:
> 
> Do you agree that this code is kind of awful ?
> 
>    static <T> T bypassCheckedException(Callable<? extends T> callable) {
>        try {
>            return callable.call();
>        } catch (Exception e) {
>            throw new IllegalStateException("task complete with exception");
>        }
>    }
> 
> so why this other one is not
> 
>    static <T> T bypassCheckedException(Callable<? extends T> callable) {
>        try(var sts = new StructuredTaskScope<>()) {
>            var task = sts.fork(callable);
>            try {
>                sts.join();
>            } catch (InterruptedException e) {
>                Thread.currentThread().interrupt();
>            }
>            return task.get();
>        }
>    }
> 
> given that it has exactly the same semantics ?
> 
> regards,
> Rémi