11.2.4 Buffered Asynchronous Channels

11.2.4.1 Creating and Using Asynchronous Channels

See also Thread Mailboxes.

An asynchronous channel is like a channel, but it buffers values so that a send operation does not wait on a receive operation.

In addition to its use with procedures that are specific to asynchronous channels, an asynchronous channel can be used as a synchronizable event (see Events). An asynchronous channel is ready for synchronization when async-channel-get would not block; the asynchronous channel’s synchronization result is the same as the async-channel-get result.

11.2.4.2 Contracts and Impersonators on Asynchronous Channels

If the c argument is a flat contract or a chaperone contract, then the result will be a chaperone contract. Otherwise, the result will be an impersonator contract.

When an async-channel/c contract is applied to an asynchronous channel, the result is not eq? to the input. The result will be either a chaperone or impersonator of the input depending on the type of contract.

The get-proc must accept the value that async-channel-get produces on channel; it must produce a replacement value, which is the result of the get operation on the impersonator.

The put-proc must accept the value passed to async-channel-put called on channel; it must produce a replacement value, which is the value passed to the put procedure called on the original channel.

The get-proc and put-proc procedures are called for all operations that get or put values from the channel, not just async-channel-get and async-channel-put.

Pairs of prop and prop-val (the number of arguments to impersonate-async-channel must be odd) add impersonator properties or override impersonator property values of channel.