Move futures out of core

[brson]

futures are not a core type and are only used by the task module. Futures are going to be redesigned to use arcs.

[eholk]

What's the plan for using futures with arcs? I'm not sure I see how arcs help futures.

[brson]

The problem with current futures is that they are not sendable, so can't be composed in useful, parallel ways. I'm thinking arcs can fix that, though I haven't thought too much about it.

[eholk]

This sounds tricky, since the future object must be mutable.

Since futures run in another task, we could just have get create a port, send a message to the task to send the value back on that port, and continue. We might also tie it to a resource that does ref counting so the task is sure to live long enough. This means get is expensive (it has to create a port), but the future could be send.

[eholk]

I was just reading over this again, and I suspect that futures are now sendable, since they use pipes and pipe endpoints are sendable.

[brson]

Awesome! That makes them much more useful.

[erickt]

Futures now are in std, so we can close this task according to the title. However, the body also mentions changing futures to use ARCs, which it doesn't use at the moment. Do we still want to make that change, or are using pipes sufficient?

[brson]

No, I think this is done.