Combine channels/ports. Allow multiple receivers

[brson]

Channels could combine the properties of channels and ports, be sendable types and allow multiple senders and receivers.

@pcwalton has suggested that this is what go does and it would seem to make channels more usable.

Likely requires copy constructors and a type that is both sendable and has destructors.

This is possibly at odds with #2157.

[graydon]

It's possible but I'm ... generally wary of this. Or at least ambivalent. Go is not the only language that does what it does, there are dozens of languages that experiment in this space. Rust's channels are half-duplex by design, following Erlang's lead. Making them full duplex means:

• reduced implementation leeway; you have fewer options on how to implement / optimize. It pretty much has to be an atomically refcounted deque with a lock on its body.
• increased inter-task synchronization on all operations; fewer chances to get the locks out of the path
• less clear ownership of in-flight data
• channels no longer weak, more stuff accidentally kept alive
• a dead consumer task no longer means data drops on the floor; it buffers forever instead

Possibly the ownership and buffer/drop (and sync/async) issues can be addressed with a richer channel API. I'm not sure the implementation flexibility or performance issues can be.

[brson]

This is not the direction we are going. Closing.