We are lacking at least one critical primitive:

• recv on port<T> with timeout that returns an option<T>

It may be desirable to recv from multiple ports at once, which may need

• recv on [port<T>] that returns (uint, T)
• recv on [port<T>] with timeout that returns option<(uint, T)>
• recv_some on [port<T>] with timeout that returns [T] or [(int, T)]
• These calls assume a fixed message type, it would be nice if it was possible to
  recv from a set of differently typed ports at once and match on the result somehow

These calls perhaps would be useful for sending to many channels:

• send_any(value: T, channels: [chan<T>]) that returns the uint vec index of the channel actually used
  • with the channel selected fairly from channels
• send_ready(value: T, channels: [chan<T>]) that returns the uint vec index of the channel actually used
  • with the channel selected fairly among ready channels from channels
• send_all(value: T, channels: [chan<T>])
  • for convenience