如何根據進程啟動后發生的事件/條件正確設置/修改值，同時在不創建競爭條件的情況下處理Goroutine 。例如，以下“有效（錯誤）”，輸出為：ping, foo=trueping, foo=falseping, foo=trueping, foo=trueping, foo=truehttps://play.golang.org/p/Y3FafF-nBcpackage mainimport "fmt"type test struct { ch chan string foo bool}func (t *test) run() { for { select { case v := <-t.ch: fmt.Printf("%+v, foo=%+v\n", v, t.foo) t.foo = false default: } }}func (t *test) Ping() { t.ch <- "ping"}func New() *test { t := &test{ ch: make(chan string), } go t.run() return t}func main() { t := New() for i := 0; i <= 10; i++ { if t.foo { t.Ping() } if i%3 == 0 { t.foo = true } }}但是，如果使用-race選項編譯或運行，我會得到以下輸出：$ go run -race main.goping, foo=true==================WARNING: DATA RACEWrite at 0x00c4200761b8 by goroutine 6: main.(*test).run() /main.go:16 +0x1fbPrevious read at 0x00c4200761b8 by main goroutine: main.main() /main.go:37 +0x5eGoroutine 6 (running) created at: main.New() /main.go:30 +0xd0 main.main() /main.go:35 +0x33==================ping, foo=falseping, foo=trueping, foo=trueping, foo=trueFound 1 data race(s)exit status 66因此，我想知道我可以使用什么并發模式來更改foogorutine 外部和 gorutine 內部的值，而不會產生競爭條件。
2 回答
子衿沉夜
TA貢獻1828條經驗 獲得超3個贊
你有一些選擇：
使用
atomic.Value：樣品 (1)使用
sync.RWMutex：樣品 (3)使用
sync/atomic：樣品 (6)僅使用通道和 goroutine：示例 (7)
另請參閱： 使用 sync.Mutex 還是通道？
1-您可以使用atomic.Value：
值提供了一致類型值的原子加載和存儲。值可以作為其他數據結構的一部分創建。Value 的零值從 Load 返回 nil。調用 Store 后，不得復制 Value。
首次使用后不得復制值。
像這個工作樣本：
// to test the panic use go build -race
package main
import (
"fmt"
"sync/atomic"
)
type test struct {
ch chan string
atomic.Value
}
func (t *test) run() {
for {
select {
case v := <-t.ch:
fmt.Printf("%+v, foo=%+v\n", v, t.Load())
t.Store(false)
default:
}
}
}
func (self *test) Ping() {
self.ch <- "ping"
}
func New() *test {
t := &test{
ch: make(chan string),
}
t.Store(false)
go t.run()
return t
}
func main() {
t := New()
for i := 0; i <= 10; i++ {
if x, _ := t.Load().(bool); x {
t.Ping()
}
// time.Sleep(time.Second)
if i%3 == 0 {
t.Store(true)
}
}
}
輸出go build -race：
ping, foo=true
ping, foo=false
ping, foo=false
ping, foo=false
ping, foo=false
2- 一點改進func (t *test) run()：
func (t *test) run() {
for v := range t.ch {
fmt.Printf("%+v, foo=%+v\n", v, t.Load())
t.Store(false)
}
}
3-您可以使用sync.RWMutexand sync.WaitGroup，就像這個工作示例一樣：
// to test the panic use go build -race
package main
import (
"fmt"
"sync"
)
type test struct {
ch chan string
foo bool
sync.RWMutex
sync.WaitGroup
}
func (t *test) run() {
for v := range t.ch {
t.Lock()
r := t.foo
t.foo = false
t.Unlock()
fmt.Printf("%+v, foo=%+v\n", v, r)
}
t.Done()
}
func (self *test) Ping() {
self.ch <- "ping"
}
func New() *test {
t := &test{ch: make(chan string)}
t.Add(1)
go t.run()
return t
}
func main() {
t := New()
for i := 0; i <= 10; i++ {
t.RLock()
r := t.foo
t.RUnlock()
if r {
t.Ping()
}
// time.Sleep(time.Second)
if i%3 == 0 {
t.Lock()
t.foo = true
t.Unlock()
}
}
close(t.ch)
t.Wait()
}
輸出go build -race：
ping, foo=true
ping, foo=true
ping, foo=false
ping, foo=true
ping, foo=false
ping, foo=true
4-所以讓我們按照這種方法https://talks.golang.org/2013/bestpractices.slide#29：
原始代碼：
package main
import (
"fmt"
"time"
)
type Server struct{ quit chan bool }
func NewServer() *Server {
s := &Server{make(chan bool)}
go s.run()
return s
}
func (s *Server) run() {
for {
select {
case <-s.quit:
fmt.Println("finishing task")
time.Sleep(time.Second)
fmt.Println("task done")
s.quit <- true
return
case <-time.After(time.Second):
fmt.Println("running task")
}
}
}
func (s *Server) Stop() {
fmt.Println("server stopping")
s.quit <- true
<-s.quit
fmt.Println("server stopped")
}
func main() {
s := NewServer()
time.Sleep(2 * time.Second)
s.Stop()
}
5-讓我們簡化它：
package main
import (
"fmt"
"time"
)
var quit = make(chan bool)
func main() {
go run()
time.Sleep(2 * time.Second)
fmt.Println("server stopping")
quit <- true // signal to quit
<-quit // wait for quit signal
fmt.Println("server stopped")
}
func run() {
for {
select {
case <-quit:
fmt.Println("finishing task")
time.Sleep(time.Second)
fmt.Println("task done")
quit <- true
return
case <-time.After(time.Second):
fmt.Println("running task")
}
}
}
輸出：
running task
running task
server stopping
finishing task
task done
server stopped
6-您的樣本的簡化版本：
// to test the panic use go build -race
package main
import "fmt"
import "sync/atomic"
var ch = make(chan string)
var state int32
func main() {
go run()
for i := 0; i <= 10; i++ {
if atomic.LoadInt32(&state) == 1 {
ch <- "ping"
}
if i%3 == 0 {
atomic.StoreInt32(&state, 1)
}
}
}
func run() {
for v := range ch {
fmt.Printf("%+v, state=%+v\n", v, atomic.LoadInt32(&state))
atomic.StoreInt32(&state, 0)
}
}
輸出：
ping, state=1
ping, state=0
ping, state=1
ping, state=0
ping, state=1
ping, state=0
7- 帶通道但不使用Lock()（The Go Playground）的工作樣本：
// to test the panic use go build -race
package main
import "fmt"
func main() {
go run()
for i := 0; i <= 10; i++ {
signal <- struct{}{}
if <-read {
ping <- "ping"
}
if i%3 == 0 {
write <- true
}
}
}
func run() {
foo := false
for {
select {
case <-signal:
fmt.Println("signal", foo)
read <- foo
case foo = <-write:
fmt.Println("write", foo)
case v := <-ping:
fmt.Println(v, foo)
foo = false
}
}
}
var (
ping = make(chan string)
signal = make(chan struct{})
read = make(chan bool)
write = make(chan bool)
)
輸出：
signal false
write true
signal true
ping true
signal false
signal false
write true
signal true
ping true
signal false
signal false
write true
signal true
ping true
signal false
signal false
write true
signal true
ping true
幕布斯6054654
TA貢獻1876條經驗 獲得超7個贊
使用互斥鎖
package main
import (
"sync"
"time"
"fmt"
)
var myvar int
var mut sync.Mutex
func main() {
for {
go other()
go printer()
time.Sleep(time.Duration(1) * time.Second)
}
}
func other() {
mut.Lock()
myvar = myvar +1
mut.Unlock()
}
func printer() {
mut.Lock()
fmt.Println(myvar)
mut.Unlock()
}
運行（使用互斥鎖）
$ go build -race t1.go
$ ./t1
1
2
3
4
5
6
7
7
9
10
運行（沒有互斥體）
$ go build t2.go
$ go build -race t2.go
$ ./t2
==================
WARNING: DATA RACE
Read at 0x000000580ce8 by goroutine 7:
runtime.convT2E()
/usr/local/go/src/runtime/iface.go:155 +0x0
main.printer()
/.../.../.../GOPATH/t2.go:23 +0x65
Previous write at 0x000000580ce8 by goroutine 6:
main.other()
/.../.../.../GOPATH/t2.go:19 +0x3d
Goroutine 7 (running) created at:
main.main()
/.../.../.../GOPATH/t2.go:13 +0x5a
Goroutine 6 (finished) created at:
main.main()
/.../.../.../GOPATH/t2.go:12 +0x42
==================
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