如何解决通道和优雅关闭死锁
运行下面的程序并运行 CTRL + C,handle
例程在尝试发送到通道时被阻止,但 process
例程已关闭。什么是更好的并发设计来解决这个问题?
编辑程序以描述应用此处建议的规则的问题https://stackoverflow.com/a/66708290/4106031
package main
import (
"context"
"fmt"
"os"
"os/signal"
"sync"
"syscall"
"time"
)
func process(ctx context.Context,c chan string) {
fmt.Println("process: processing (select)")
for {
select {
case <-ctx.Done():
fmt.Printf("process: ctx done bye\n")
return
case i := <-c:
fmt.Printf("process: received i: %v\n",i)
}
}
}
func handle(ctx context.Context,readChan <-chan string) {
c := make(chan string,1)
wg := &sync.WaitGroup{}
wg.Add(1)
go func() {
process(ctx,c)
wg.Done()
}()
defer wg.Wait()
for i := 0; ; i++ {
select {
case <-ctx.Done():
fmt.Printf("handle: ctx done bye\n")
return
case i := <-readChan:
fmt.Printf("handle: received: %v\n",i)
fmt.Printf("handle: sending for processing: %v\n",i)
// suppose huge time passes here
// to cause the issue we want to happen
// we want the process() to exit due to ctx
// cancellation before send to it happens,this creates deadlock
time.Sleep(5 * time.Second)
// deadlock
c <- i
}
}
}
func main() {
wg := &sync.WaitGroup{}
ctx,cancel := context.WithCancel(context.Background())
defer cancel()
readChan := make(chan string,10)
wg.Add(1)
go func() {
defer wg.Done()
for i := 0; ; i++ {
select {
case <-ctx.Done():
fmt.Printf("read: ctx done bye\n")
return
case readChan <- fmt.Sprintf("%d",i):
fmt.Printf("read: sent msg: %v\n",i)
}
}
}()
wg.Add(1)
go func() {
handle(ctx,readChan)
wg.Done()
}()
go func() {
sigterm := make(chan os.Signal,1)
signal.Notify(sigterm,syscall.SIGINT,syscall.SIGTERM)
select {
case <-sigterm:
fmt.Printf("SIGTERM signal received\n")
cancel()
}
}()
wg.Wait()
}
$ go run chan-shared.go
read: sent msg: 0
read: sent msg: 1
read: sent msg: 2
read: sent msg: 3
process: processing (select)
read: sent msg: 4
read: sent msg: 5
read: sent msg: 6
handle: received: 0
handle: sending for processing: 0
read: sent msg: 7
read: sent msg: 8
read: sent msg: 9
read: sent msg: 10
handle: received: 1
handle: sending for processing: 1
read: sent msg: 11
process: received i: 0
process: received i: 1
read: sent msg: 12
handle: received: 2
handle: sending for processing: 2
^CSIGTERM signal received
process: ctx done bye
read: ctx done bye
handle: received: 3
handle: sending for processing: 3
Killed: 9
解决方法
分步回顾
- 始终取消上下文,无论您怎么想。
ctx,cancel := context.WithCancel(context.Background())
defer cancel()
- 开始例程后不要 wd.Add
wg.Add(1)
go handle(ctx,wg)
- 不要稀疏地使用等待组
wg.Add(1)
go func() {
handle(ctx)
wg.Done()
}()
- 不要在默认情况下在频道上循环。只需读取它并让它解锁
<-sigterm
fmt.Printf("SIGTERM signal received\n")
- main 从不阻塞信号,主要阻塞处理例程。信令应该只做信令,即取消上下文。
go func() {
sigterm := make(chan os.Signal,1)
signal.Notify(sigterm,syscall.SIGINT,syscall.SIGTERM)
<-sigterm
fmt.Printf("SIGTERM signal received\n")
cancel()
}()
- 可以检查通道写入的上下文取消。
select {
case <-ctx.Done():
fmt.Printf("process: ctx done bye\n")
return
case c <- fmt.Sprintf("%d",i):
fmt.Printf("handled: sent to channel: %v\n",i)
}
- 不要计时。睡眠,你不能用它测试上下文取消。
select {
case <-ctx.Done():
fmt.Printf("process: ctx done bye\n")
return
case <-time.After(time.Second * 5):
}
因此,应用了各种规则的完整修订版代码为我们提供了
package main
import (
"context"
"fmt"
"os"
"os/signal"
"sync"
"syscall"
"time"
)
func process(ctx context.Context,c chan string) {
fmt.Println("process: processing (select)")
for {
select {
case <-ctx.Done():
fmt.Printf("process: ctx done bye\n")
return
case msg := <-c:
fmt.Printf("process: got msg: %v\n",msg)
}
}
}
func handle(ctx context.Context) {
c := make(chan string,3)
wg := &sync.WaitGroup{}
wg.Add(1)
go func() {
process(ctx,c)
wg.Done()
}()
defer wg.Wait()
for i := 0; ; i++ {
select {
case <-ctx.Done():
fmt.Printf("process: ctx done bye\n")
return
case <-time.After(time.Second * 5):
}
select {
case <-ctx.Done():
fmt.Printf("process: ctx done bye\n")
return
case c <- fmt.Sprintf("%d",i)
}
}
}
func main() {
wg := &sync.WaitGroup{}
ctx,cancel := context.WithCancel(context.Background())
defer cancel()
wg.Add(1)
go func() {
handle(ctx)
wg.Done()
}()
go func() {
sigterm := make(chan os.Signal,syscall.SIGTERM)
<-sigterm
fmt.Printf("SIGTERM signal received\n")
cancel()
}()
wg.Wait()
}
关于退出条件还有很多要说的,但这取决于要求。
,如前所述 https://stackoverflow.com/a/66708290/4106031 此更改已为我解决了该问题。也感谢 mh-cbon 的规则!
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