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Version: 4.2.1
10.2.2 Channels

A channel both synchronizes a pair of threads and passes a value from one to the other. Channels are synchronous; both the sender and the receiver must block until the (atomic) transaction is complete. Multiple senders and receivers can access a channel at once, but a single sender and receiver is selected for each transaction.

Channel synchronization is fair: if a thread is blocked on a channel and transaction opportunities for the channel occur infinitely often, then the thread eventually participates in a transaction.

For buffered asynchronous channels, see Buffered Asynchronous Channels.

Creates and returns a new channel. The channel can be used with channel-get, with channel-try-get, or as a synchronizable event (see Events) to receive a value through the channel. The channel can be used with channel-put or through the result of channel-put-evt to send a value through the channel.

(channel? v)  boolean?
  v : any/c
Returns #t if v is a channel created by make-channel, #f otherwise.

(channel-get ch)  any
  ch : channel?
Blocks until a sender is ready to provide a value through ch. The result is the sent value.

(channel-try-get ch)  any
  ch : channel?
Receives and returns a value from ch if a sender is immediately ready, otherwise returns #f.

(channel-put ch v)  void?
  ch : channel?
  v : any/c
Blocks until a receiver is ready to accept the value v through ch.

(channel-put-evt ch v)  evt?
  ch : channel?
  v : any/c
Returns a fresh synchronizable event for use with sync. The event is ready when (channel-put ch v) would not block, and the event’s synchronization result is the event itself.