Make notify return a promise derived from onProgress return values/throws.

[domenic]

See promises-aplus/progress-spec#3 (comment). This would replace our current strategy of crashing if onProgress throws.

I believe it would be something along the lines of Q.all(progressHandlers.map(Q.fcall)).

[kriskowal]

This change could not land until v2. As it happens, notify and progress have been removed outright in v2, and if they are reintroduced, will not compose. Closing.

[TimDaub]

I'm trying to abort the hashing of a number of files and I'm using Q's promises to handle the async part.
So since this is never going to work in 1.0, I guess its not possible to stop the execution of a promise from the outside or is it?

[kriskowal]

@TomDaub cancellation is an unrelated concern to progress/notify. Q promises have multiple consumer semantics, so cancellation is tricky. I am contemplating building a library with a "task" primitive that is similar to a promise but with explicit fork() and cancel(), and @domenic is actively working out whether promises can become cancelable promises with reference counting on observers.

See: https://github.com/kriskowal/gtor