What is the recommended way to cancel promise collections?

This library provides several promise collection primitives, which all have valid use cases.

One might assume the following is the way to go:

$promises = array(
    accessSomeRemoteResource(),
    accessSomeRemoteResource(),
    accessSomeRemoteResource()
);

$promise = \React\Promise\all($promises);

// what does this do?
$promise->cancel();

How does this cope with cancellation support?

This is currently not implemented, i.e. calling cancel() currently has no effect.

Should we consider adding this?

Also, if yes, how could cancellation support work for the other primitives?