11.2.4 Buffered Asynchronous Channels (original) (raw)
11.2.4 Buffered Asynchronous Channels🔗ℹ
11.2.4.1 Creating and Using Asynchronous Channels🔗ℹ
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 asynchronizable event (see Events). An asynchronous channel is ready for synchronization whenasync-channel-get would not block; the asynchronous channel’ssynchronization result is the same as theasync-channel-get result.
Returns #t if v is an asynchronous channel,#f otherwise.
Returns an asynchronous channel with a buffer limit of limititems. A get operation blocks when the channel is empty, and a put operation blocks when the channel has limit items already. If limit is #f, the channel buffer has no limit (so a put never blocks).
Blocks until at least one value is available in ach, and then returns the first of the values that were put intoasync-channel.
If at least one value is immediately available in ach, returns the first of the values that were put into ach. Ifasync-channel is empty, the result is #f.
Puts v into ach, blocking if ach’s buffer is full until space is available.
Returns a synchronizable event that is ready for synchronization when (async-channel-put ach v) would return a value (i.e., when the channel holds fewer values already than its limit); the synchronization result of a asynchronous channel-put event is the asynchronous channel-put event itself.
Examples:
(define (server input-channel output-channel) (thread (lambda () (define (get) (async-channel-get input-channel)) (define (put x) (async-channel-put output-channel x)) (define (do-large-computation) (sqrt 9)) (let loop ([data (get)]) (case data [(quit) (void)] [(add) (begin (put (+ 1 (get))) (loop (get)))] [(long) (begin (put (do-large-computation)) (loop (get)))])))))(define to-server (make-async-channel))(define from-server (make-async-channel)) > (server to-server from-server) # > (async-channel? to-server) #t > (printf "Adding 1 to 4\n") Adding 1 to 4 > (async-channel-put to-server 'add) > (async-channel-put to-server 4) > (printf "Result is ~a\n" (async-channel-get from-server)) Result is 5 > (printf "Ask server to do a long computation\n") Ask server to do a long computation > (async-channel-put to-server 'long) > (printf "I can do other stuff\n") I can do other stuff > (printf "Ok, computation from server is ~a\n" (async-channel-get from-server)) Ok, computation from server is 3 > (async-channel-put to-server 'quit)
11.2.4.2 Contracts and Impersonators on Asynchronous Channels🔗ℹ
Returns a contract that recognizes asynchronous channels. Values put into or retrieved from the channel must match c.
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 achaperone or impersonator of the input depending on the type of contract.
Returns an impersonator of channel, which redirects theasync-channel-get and async-channel-put operations.
The get-proc must accept the value that async-channel-getproduces 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-putcalled 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 justasync-channel-get and async-channel-put.
Pairs of prop and prop-val (the number of arguments toimpersonate-async-channel must be odd) addimpersonator properties or override impersonator property values of channel.
Like impersonate-async-channel, but the get-proc procedure must produce the same value or a chaperone of the original value, andput-proc must produce the same value or a chaperone of the original value.