bergus / creed Goto Github PK

Currently cancellation callbacks from subscribe, subscribeOrCall, finally and trifurcate are called synchronously from cancel(…). They should not.
This was done to a) immediately cancel involved promises and actions (not just by .requested) and b) create and flatten the array of feedback promises from the appropriate sources. See bergus/promise-cancellation#7 and bergus/promise-cancellation#9.

See the case made by @stefanpenner in tc39/proposal-cancelable-promises#52

In many situations, a long-lived cancellation token (passed in by the caller) is combined with a short-lived token, e.g. in the "last" example or for a timeout:

function withTimeout(action, t) {
    return function(...args) {
        const token = args.pop();
        const timeout = new CancelToken(cancel => setTimeout(cancel, t, "timeout"));
        return action.call(this, ...args, token.concat(timeout));
    };
}

When the action is long over, and the combined token is no longer relevant to anyone, the token still holds are reference to it.
Todo:

• ensure that it is dropped, or at least not more than a constant amount of references are kept (though not ideal for tree-like dependencies).
• write refcounting test

A token that is cancelled after a timeout is simple:

new CancelToken(cancel => setTimeout(cancel, t, "timeout"))

However, this keeps the setTimeout active even when the token is no longer needed and all promises that might be cancelled by it are already resolved. This could keep a process alive even when there's nothing to do any more.
Implement a TimeoutToken that does not need any resources while nobody is listening, i.e. simply stores the end time and calls setTimeout/clearTimeout as necessary.
In node, this also could be achieved by a simple unref call.