Go language programming

Concurrency: goroutines and channels The Go language has built-in facilities, as well as library support, for writing concurrent programs. Concurrency refers not only to CPU parallelism, but also to asynchrony: letting slow operations like a database or network read run while the program does other work, as is common in event-based servers.[78] The primary concurrency construct is the goroutine, a type of light-weight process. A function call prefixed with the go keyword starts a function in a new goroutine. The language specification does not specify how goroutines should be implemented, but current implementations multiplex a Go process's goroutines onto a smaller set of operating-system threads, similar to the scheduling performed in Erlang.[79]:10 While a standard library package featuring most of the classical concurrency control structures (mutex locks, etc.) is available,[79]:151–152 idiomatic concurrent programs instead prefer channels, which provide send messages between goroutines.[80] Optional buffers store messages in FIFO order[62]:43 and allow sending goroutines to proceed before their messages are received.[citation needed] Channels are typed, so that a channel of type chan T can only be used to transfer messages of type T. Special syntax is used to operate on them; <-ch is an expression that causes the executing goroutine to block until a value comes in over the channel ch, while ch <- x sends the value x (possibly blocking until another goroutine receives the value). The built-in switch-like select statement can be used to implement non-blocking communication on multiple channels; see below for an example. Go has a memory model describing how goroutines must use channels or other operations to safely share data.[81] The existence of channels sets Go apart from actor model-style concurrent languages like Erlang, where messages are addressed directly to actors (corresponding to goroutines). The actor style can be simulated in Go by maintaining a one-to-one correspondence between goroutines and channels, but the language allows multiple goroutines to share a channel or a single goroutine to send and receive on multiple channels.[79]:147 From these tools one can build concurrent constructs like worker pools, pipelines (in which, say, a file is decompressed and parsed as it downloads), background calls with timeout, "fan-out" parallel calls to a set of services, and others.[82] Channels have also found uses further from the usual notion of interprocess communication, like serving as a concurrency-safe list of recycled buffers,[83] implementing coroutines (which helped inspire the name goroutine),[84] and implementing iterators.[85] Concurrency-related structural conventions of Go (channels and alternative channel inputs) are derived from Tony Hoare's communicating sequential processes model. Unlike previous concurrent programming languages such as Occam or Limbo (a language on which Go co-designer Rob Pike worked),[86] Go does not provide any built-in notion of safe or verifiable concurrency.[87] While the communicating-processes model is favored in Go, it is not the only one: all goroutines in a program share a single address space. This means that mutable objects and pointers can be shared between goroutines; see § Lack of race condition safety, below.[citation needed]