GO语言：致命错误：所有goroutine都在睡眠中-死锁

Z时代
2024-01-10
分类：问答

下面的代码与硬编码的JSON数据一起正常工作，但是当我从文件中读取JSON数据时不起作用。我得到fatal error: all goroutines

are asleep - deadlock使用时的错误sync.WaitGroup。

package main
import (
    "bytes"
    "fmt"
    "os/exec"
    "time"
)
func connect(host string) {
    cmd := exec.Command("ssh", host, "uptime")
    var out bytes.Buffer
    cmd.Stdout = &out
    err := cmd.Run()
    if err != nil {
        fmt.Println(err)
    }
    fmt.Printf("%s: %q\n", host, out.String())
    time.Sleep(time.Second * 2)
    fmt.Printf("%s: DONE\n", host)
}
func listener(c chan string) {
    for {
        host := <-c
        go connect(host)
    }
}
func main() {
    hosts := [2]string{"user1@111.79.154.111", "user2@111.79.190.222"}
    var c chan string = make(chan string)
    go listener(c)
    for i := 0; i < len(hosts); i++ {
        c <- hosts[i]
    }
    var input string
    fmt.Scanln(&input)
}

user@user-VirtualBox:~/go$ go run channel.go user1@111.79.154.111: " 09:46:40 up 86 days, 18:16, 0 users, load average: 5" user2@111.79.190.222: " 09:46:40 up 86 days, 17:27, 1 user, load average: 9" user1@111.79.154.111: DONE user2@111.79.190.222: DONE

package main
import (
    "bytes"
    "fmt"
    "os/exec"
    "time"
    "encoding/json"
    "os"
    "sync"
)
func connect(host string) {
    cmd := exec.Command("ssh", host, "uptime")
    var out bytes.Buffer
    cmd.Stdout = &out
    err := cmd.Run()
    if err != nil {
        fmt.Println(err)
    }
    fmt.Printf("%s: %q\n", host, out.String())
    time.Sleep(time.Second * 2)
    fmt.Printf("%s: DONE\n", host)
}
func listener(c chan string) {
    for {
        host := <-c
        go connect(host)
    }
}
type Content struct {
    Username string `json:"username"`
    Ip       string `json:"ip"`
}
func main() {
    var wg sync.WaitGroup
    var source []Content
    var hosts []string
    data := json.NewDecoder(os.Stdin)
    data.Decode(&source)
    for _, value := range source {
        hosts = append(hosts, value.Username + "@" + value.Ip)
    }
    var c chan string = make(chan string)
    go listener(c)
    for i := 0; i < len(hosts); i++ {
        wg.Add(1)
        c <- hosts[i]
        defer wg.Done()
    }
    var input string
    fmt.Scanln(&input)
    wg.Wait()
}

user@user-VirtualBox:~/go$ go run deploy.go < hosts.txt user1@111.79.154.111: " 09:46:40 up 86 days, 18:16, 0 users, load average: 5" user2@111.79.190.222: " 09:46:40 up 86 days, 17:27, 1 user, load average: 9" user1@111.79.154.111 : DONE user2@111.79.190.222: DONE fatal error: all goroutines are asleep - deadlock! goroutine 1 [semacquire]: sync.runtime_Semacquire(0xc210000068) /usr/lib/go/src/pkg/runtime/sema.goc:199 +0x30 sync.(*WaitGroup).Wait(0xc210047020) /usr/lib/go/src/pkg/sync/waitgroup.go:127 +0x14b main.main() /home/user/go/deploy.go:64 +0x45a goroutine 3 [chan receive]: main.listener(0xc210038060) /home/user/go/deploy.go:28 +0x30 created by main.main /home/user/go/deploy.go:53 +0x30b exit status 2 user@user-VirtualBox:~/go$

[
   {
      "username":"user1",
      "ip":"111.79.154.111"
   },
   {
      "username":"user2",
      "ip":"111.79.190.222"
   }
]

回答：

从语言规范

程序执行首先初始化主程序包，然后调用函数main。当该函数调用返回时，程序退出。它不等待其他（非主）goroutine完成。

因此，您需要等待goroutine完成。常见的解决方案是使用sync.WaitGroup对象。

最简单的同步goroutine的代码：

package main
import "fmt"
import "sync"
var wg sync.WaitGroup // 1
func routine() {
    defer wg.Done() // 3
    fmt.Println("routine finished")
}
func main() {
    wg.Add(1) // 2
    go routine() // *
    wg.Wait() // 4
    fmt.Println("main finished")
}

并用于同步多个goroutine

package main
import "fmt"
import "sync"
var wg sync.WaitGroup // 1
func routine(i int) {
    defer wg.Done() // 3
    fmt.Printf("routine %v finished\n", i)
}
func main() {
    for i := 0; i < 10; i++ {
        wg.Add(1) // 2
        go routine(i) // *
    }
    wg.Wait() // 4
    fmt.Println("main finished")
}