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demo66.go
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demo66.go
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package main
import (
"errors"
"fmt"
"sync"
"sync/atomic"
"time"
)
func main() {
var counter uint32
var once sync.Once
once.Do(func() {
atomic.AddUint32(&counter, 1)
})
fmt.Printf("The counter: %d\n", counter)
once.Do(func() {
atomic.AddUint32(&counter, 2)
})
fmt.Printf("The counter: %d\n", counter)
fmt.Println()
once = sync.Once{}
var wg sync.WaitGroup
wg.Add(3)
go func() {
defer wg.Done()
once.Do(func() {
for i := 0; i < 3; i++ {
fmt.Printf("Do task. [1-%d]\n", i)
time.Sleep(time.Second)
}
})
fmt.Println("Done. [1]")
}()
go func() {
defer wg.Done()
time.Sleep(time.Millisecond * 500)
once.Do(func() {
fmt.Println("Do task. [2]")
})
fmt.Println("Done. [2]")
}()
go func() {
defer wg.Done()
time.Sleep(time.Millisecond * 500)
once.Do(func() {
fmt.Println("Do task. [3]")
})
fmt.Println("Done. [3]")
}()
wg.Wait()
fmt.Println()
once = sync.Once{}
wg.Add(2)
go func() {
defer wg.Done()
defer func() {
if p := recover(); p != nil {
fmt.Printf("fatal error: %v\n", p)
}
}()
once.Do(func() {
fmt.Println("Do task. [4]")
panic(errors.New("something wrong"))
fmt.Println("Done. [4]")
})
}()
go func() {
defer wg.Done()
time.Sleep(time.Millisecond * 500)
once.Do(func() {
fmt.Println("Do task. [5]")
})
fmt.Println("Done. [5]")
}()
wg.Wait()
}