Go WaitGroup: Difference between revisions
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The main goroutine calls <code>Add()</code> to set the number of goroutines to wait for. Then it can block on <code>Wait()</code> until all other goroutines have finished. When each of the counted goroutines runs, they should call <code>Done()</code> when finished, to increment the counting semaphore. | The main goroutine calls <code>Add()</code> to set the number of goroutines to wait for. Then it can block on <code>Wait()</code> until all other goroutines have finished. When each of the counted goroutines runs, they should call <code>Done()</code> when finished, to increment the counting semaphore. | ||
<syntaxhighlight lang='go'> | |||
func aFunction(wg *sync.WaitGroup, s string) { | |||
defer wg.Done() | |||
fmt.Println(s) | |||
} | |||
... | |||
wg := sync.WaitGroup{} | |||
wg.Add(2) | |||
go aFunction(&wg, "A") | |||
go aFunction(&wg, "B") | |||
wg.Wait() | |||
fmt.Println("main is done") | |||
</syntaxhighlight> | |||
Note that the <code>WaitGroup</code> instance must be passed to the functions executed on the counted goroutines '''by pointer''', not value. <font color=darkkhaki>Why?</font> | Note that the <code>WaitGroup</code> instance must be passed to the functions executed on the counted goroutines '''by pointer''', not value. <font color=darkkhaki>Why?</font> | ||
Revision as of 21:36, 1 September 2023
External
Internal
Overview
A WaitGroup is a counting semaphore that waits for a set of goroutines to finish.
The main goroutine calls Add() to set the number of goroutines to wait for. Then it can block on Wait() until all other goroutines have finished. When each of the counted goroutines runs, they should call Done() when finished, to increment the counting semaphore.
func aFunction(wg *sync.WaitGroup, s string) {
defer wg.Done()
fmt.Println(s)
}
...
wg := sync.WaitGroup{}
wg.Add(2)
go aFunction(&wg, "A")
go aFunction(&wg, "B")
wg.Wait()
fmt.Println("main is done")
Note that the WaitGroup instance must be passed to the functions executed on the counted goroutines by pointer, not value. Why?