What happens in the case of multiple senders/receivers?

[gopherbot]

by josef.svenningsson:

The Go language specification is silent about what happens if there are
multiple senders and/or receivers on a channel. Suppose there are two
receivers blocked, waiting to receive from a channel. When a sender sends a
value on the channel, who gets it?

If I had a say in the matter I would go for the natural and intuitive FIFO
semantics where the receiver which was first to block is the one to receive
a message when it becomes available. Same thing for blocking senders.

[gopherbot]

Comment 1 by dark.nowhere:

I think the standard interpretation of multiple receivers on a channel is that they
are receiving work that any one of them is capable of handling. If you try to get
away from this model you will end up with:
a) hairy stuff in the implementation to guarantee the behavior, and
b) far worse, a debugging nightmare for any code you write that intends to take
advantage of it. 
Eg. what if your intended first receiver is delayed or fails completely?
If you really need to have receivers consuming according to some defined order it
seems more like a synchronization issue to me -- you can use, for example, (other)
channels to sync up your multiple receivers so that they process things in your
intended order. This brings the advantage of explicit behavior in your code and
guaranteed behavior, not to mention greater flexibility than any built-in.

[gopherbot]

Comment 2 by josef.svenningsson:

If there is no specified order then the implementation is free to starve a process
completely, something which I think no-one would be happy with. Some kind of fairness
guarantees are crucial to have in order to make sure that all goroutines can have a
go at evaluating.
So, this isn't an issue about being able to control in what order things are
happening. My concern is that some goroutine may never get the chance to do its job
if the order among receivers is undefined.

[agl]

Comment 3:

This is a mailing list topic, not a bug.

Status changed to Invalid.