Channel (programming): Difference between revisions

Revision as of 06:47, 6 October 2014

Revision as of 01:23, 10 May 2015

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{{About-distinguish|software interprocess communication|Channel (communications)}}

In computing, a '''channel''' is a model for [[interprocess communication]] and [[synchronization]] via [[message passing]]. A message may be sent over a channel, and another process or thread is able to synchronously receive messages sent over a channel it has a [[reference (computer science)|reference]] to, as a [[stream (computing)|stream]].

In computing, a '''channel''' is a model for [[interprocess communication]] and [[synchronization]] via [[message passing]]. A message may be sent over a channel, and another process or thread is able to synchronously receive messages sent over a channel it has a [[reference (computer science)|reference]] to, as a [[stream (computing)|stream]]. Different implementations of channels may be buffered or not, and either synchronous or asynchronous.

Channels are fundamental to the [[process calculus]] approach to concurrency, and first originated in [[communicating sequential processes]] (CSP), a formal model for concurrency, and has been used in many derived languages, such as [[occam (programming language)|occam]], and [[Limbo programming language]] (via [[Newsqueak]] and the [[Alef programming language]]). They are also used in the [[C programming language]] threading library libthread, and in [[Plan 9 from Bell Labs]], which uses libthread, as well as in [[Stackless Python]] and the [[Go programming language]].

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==Channel implementations==

Most Channel implementations areChannels modeled close toafter the CSP model. Channels are inherently [[Synchronization (computer science)|synchronous]]: a process waiting to receive an object from a channel will [[Blocking_(computing)|block]] until the object is sent. This is also called [[rendezvous behaviour]].

Typical supported operations are presented below using the example of the [[libthread]] channel API.

* Channel creation of fixed or variable size, returning a [[reference]] or [[Reference (computer science)|handle]] <source lang="c">Channel* chancreate(int elemsize, int bufsize)</source>

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===libthread channels===

The [[Multithreading (computer architecture)|Multithreading]] library, [[libthread]], which was first created for the operating system [[Plan 9 from Bell Labs|Plan 9]] and later adopted by several Unix systems as well, offers inter-thread communication based on fixed-size channels.

===OCaml events===

The [[OCaml]] event module offers typed channels for synchronization. When the module's send and receive functions are called, they create corresponding send and receive events which can be synchronized.

== Examples ==

=== XMOS XC ===

The [[XMOS|XMOS]] programming language [[XC (programming language)|XC]] provides a primitive type "chan" and two operators "<:" and ":>" for sending and receiving data from a channel. <ref>https://www.xmos.com/node/17653?version=&page=23</ref>

In this example, two hardware threads are started on the XMOS, running the two lines in the "par" block. The first line transmits the number 42 through the channel while the second waits until it is received and sets the value of x. The XC language also allows asynchronous receiving on channels through a select statement.

<source lang="c">

chan c;

int x;

par {

c <: 42;

c :> x;

}

</source>

=== Go ===

This snippet of Go code performs similarly to the XC code. First the channel c is created, then a goroutine is spawned which sends 42 through the channel. When the number is put in the channel x is set to 42. Go allows channels to buffer contents, as well as non blocking receiving through the use of a select block.<ref>https://golang.org/doc/effective_go.html#channels</ref>

<source lang="go">

c := make(chan int)

go func() {c <- 42}()

x := <- c

</source>

== Applications ==