Go Language Goroutines
Internal
Overview
A goroutine is a Go thread. Many goroutines execute within a single O/S thread, the main thread?. From the O/S point of view, only one thread is scheduled. The goroutine schedule is done by the Go runtime scheduler. The Go runtime scheduler uses a logical processor. The goroutines scheduled on a logical processor are executing concurrently, not |in parallel. However, it is possible to have more than one logical processor, each logical processors can be mapped onto an O/S thread, which may be scheduled to work on different cores. In this case, things may become parallel.
A goroutine is always created automatically, to run the main()
function.
Creation and Invocation
To explicitly create a goroutine and schedule it, use the go
keyword, by providing a function invocation.
func somefunc(i int) {
...
}
...
go somefunc(10)
Any function invocation can be used: go fmt.Printf("something")
.
Note that this syntax only schedules a goroutine. It is not determined when it will be actually executed.
what happens with the result of the function?
If the invocation is done from main()
, the scheduler always seems to continue to execute main()
, it does not preempt main()
to executes the new goroutine. Also, given the fact that when main()
exists, all other goroutines are forcibly terminated, unless there's a mechanism that ensures they will be executed, they might not be executed at all. It is bad practice to use time.Sleep()
to preempt and delay main()
, because we're making assumptions about timing, and these assumptions can be wrong, and also we're assuming that the scheduler will schedule the other goroutine.
Exiting
A goroutine exits when the code is complete.
When the main
goroutine is complete, all other goroutines are forced to exit. It is said that those goroutines exit early.