Loom Evades Exception Handling

[Remi Forax]

Hi Eric,
getRemoteString() returns a Stream, and a Stream delays the call to the intermediary operations to the point where the terminal operation, here forEach(), is called.
When forEach() is called, the executor is already closed, so forEach() calls map() that calls fork() that throws an IllegalStateException.

I see no issue here, if you return a List instead of a Stream, you will have the behavior I believe you want.

regards,
Rémi

----- Original Message -----
> From: "Eric Kolotyluk" <eric at kolotyluk.net>
> To: "loom-dev" <loom-dev at openjdk.java.net>
> Sent: Jeudi 25 Novembre 2021 21:27:04
> Subject: Loom Evades Exception Handling

> Yes, that subject line is click-bait, but this is not intuitive to me... Am
> I just seeing an incomplete implementation of Project Loom, and this will
> be resolved in the future?
> 
> public class Experiment06 {
> 
>    public static void main(String args[]) {
>        Context.printHeader(Experiment06.class);
> 
>        try {
>            getRemoteStrings().forEach(System.out::println);
>        } catch (ExperimentException e) {
>            e.printStackTrace();
>        }
>    }
> 
>    static Stream<String> getRemoteStrings() throws ExperimentException {
> 
>        try (var structuredExecutor = StructuredExecutor.open("Experiment06")) {
> 
>            // We want complete results, so we won't tolerate failure.
>            var completionHandler = new StructuredExecutor.ShutdownOnFailure();
> 
>            var futureResults = IntStream.range(0, 15).mapToObj(item -> {
>                try {
>                    System.out.printf("item = %d, Thread ID = %s\n",
> item, Thread.currentThread());
>                    return structuredExecutor.fork(() -> {
>                        try {
>                            System.out.printf("\ttask = %d, Thread ID
> = %s\n", item, Thread.currentThread());
>                            return getRemoteString(item, new
> URI("https://server1/foobar.com/item"));
>                        }
>                        catch (Throwable t) {
>                            System.out.printf("TASK EXCEPTION
> %s\n\t%s\n\n", t.getMessage(), t.getCause());
>                            t.printStackTrace();
>                            throw t;
>                        }
>                    }, completionHandler);
>                } catch (Throwable t) {
>                    System.out.printf("SPAWN EXCEPTION %s\n\t%s\n\n",
> t.getMessage(), t.getCause());
>                    t.printStackTrace();
>                    throw t;
>                }
>            });
>            structuredExecutor.joinUntil(Instant.now().plusSeconds(10));
>            completionHandler.throwIfFailed();
>            return futureResults.map(Future::resultNow);
>        }
>        catch  (InterruptedException e) {
>            e.printStackTrace();
>            throw new ExperimentException(e);
>        } catch (ExecutionException e) {
>            e.printStackTrace();
>            throw new ExperimentException(e);
>        } catch (TimeoutException e) {
>            e.printStackTrace();
>            throw new ExperimentException(e);
>        } catch (IllegalStateException e) {
>            e.printStackTrace();
>            throw new ExperimentException(e);
>        }
>        catch (Throwable t) {
>            t.printStackTrace();
>            throw new ExperimentException(t);
>        }
>    }
> 
>    static String getRemoteString(int item, URI from) {
>        return "Item %d from %s".formatted(item, from);
>    }
> 
>    static class ExperimentException extends Exception {
>        ExperimentException(Throwable cause) {
>            super(cause);
>        }
>    }
> }
> 
> where I get
> 
> [image: image.png]
> 
> 
> (Experiment06.java:50) is
> 
> return structuredExecutor.fork(() -> {
> 
> (Experiment06.java:34) is
> 
> getRemoteStrings().forEach(System.out::println);
> 
> Is there some way I can actually find out more from the Exception handling,
> or other techniques?
> 
> Cheers, Eric