Ask HN: Why don't languages that support Promises include timeouts?

8 points0x0aff3746686y ago4 comments

I've been programming with promises for several years now, and I find myself using a common pattern of adding a race timeout promise. It seems like a useful feature, why isn't it implicit when dealing with deferred execution? I run into very few cases where an infinite timeout period makes sense.

4 comments

komon6y ago

You're not the only person to be asking this question recently!

Kyle Simpson (@getify on twitter and github) of You Don't Know JS fame has been working on a library for Javascript that wraps generators in a way that:

a) lets you use other Promise workflows to interact with them

b) lets you create a cancellation token that can be passed to a chain of asynchronous work to allow jobs to be cancelled all the way down that chain

among other goodies. Even if you're not working in the JS space, it's some really cool work to read about[1]

[1]https://github.com/getify/CAF

0x0aff374668OP6y ago

Whoa. That's brilliant. Thanks!

SamReidHughes6y ago

Well, you have to cancel the task, not ignore it. So you need some standard cancellation hook. And that generally has to be something explicitly handled by the task in question; it cannot automatically percolate all the way down to the deepest sub-task.

If your promise lib has cancellation built in, then adding a timeout to one is easy.

0x0aff374668OP6y ago

oh, shit. that means if i just send a timeout promise and a worker promise to Promise.race([...]), and the timeout finishes but the worker never does... then I have some unfulfilled promise hanging out somewhere indefinitely? I guess so... if I do Promise.race([p1, p2]) and p1 fulfills and p2 doesn't, p2 is still alive...indefinitely. Am I right or wrong...?

j / k navigate · click thread line to collapse

4 comments

komon6y ago

You're not the only person to be asking this question recently!

Kyle Simpson (@getify on twitter and github) of You Don't Know JS fame has been working on a library for Javascript that wraps generators in a way that:

a) lets you use other Promise workflows to interact with them

b) lets you create a cancellation token that can be passed to a chain of asynchronous work to allow jobs to be cancelled all the way down that chain

among other goodies. Even if you're not working in the JS space, it's some really cool work to read about[1]

[1]https://github.com/getify/CAF

0x0aff374668OP6y ago

Whoa. That's brilliant. Thanks!

SamReidHughes6y ago

If your promise lib has cancellation built in, then adding a timeout to one is easy.

0x0aff374668OP6y ago

j / k navigate · click thread line to collapse