通道和正常关机死锁
运行以下程序并运行CTRL + C，例程在尝试发送到通道但例程已关闭时被阻止。什么是更好的并发设计来解决这个问题？handleprocess
已编辑程序以应用此处建议的规则来描述问题，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)
}
}
}
GCT10152回答
-
PIPIONE
分步回顾无论你怎么想，总是取消上下文。ctx, cancel := context.WithCancel(context.Background())defer cancel()不要说。启动例程后添加 wg.Add(1) go handle(ctx, wg)不要稀疏地消耗等待组 wg.Add(1) go func() { handle(ctx) wg.Done() }()不要在具有默认大小写的通道上循环。只需从中读取并让它解锁 <-sigterm fmt.Printf("SIGTERM signal received\n")主从不阻塞信号，主块在处理例程上。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() }()可以检查通道写入时的上下文取消。 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) }不要花时间。睡眠，您无法用它来测试上下文取消。 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 mainimport ( "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): fmt.Printf("handled: sent to channel: %v\n", 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, 1) signal.Notify(sigterm, syscall.SIGINT, syscall.SIGTERM) <-sigterm fmt.Printf("SIGTERM signal received\n") cancel() }() wg.Wait()}关于退出条件还有更多要讲的，但这取决于要求。 -
Smart猫小萌
如前所述 https://stackoverflow.com/a/66708290/4106031 此更改为我解决了问题。也感谢mh-cbon的规则！
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