Go Package sync

External

• https://golang.org/pkg/sync

Internal

• Standard Library
• The "atomic" package

Overview

The "sync" package provides synchronization primitives, to be used when synchronization between goroutines is needed.

WaitGroup

• sync.WaitGroup

A WaitGroup is a counting semaphore that waits for a collection of goroutines to finish. The main goroutine calls Add() to set the number of goroutines to wait for. Then each of the goroutines runs and calls Done() when finished. At the same time, Wait() can be used to block until all goroutines have finished.

Using a waitGroup to wait for goroutines to finish before exiting main(): playground/go/concurrency/waitGroup.go

Mutex

• sync.Mutex

A Mutex is a mutual exclusion lock. Only one goroutine can enter the critical section at a time. Not until the call to the Unlock() function issued can another goroutine enter the critical section.

Usage pattern (the curly braces are not necessary):

var mutex sync.Mutex

...

mutex.Lock() {
    // do something in a mutual exclusion mode
}

mutex.Unlock()