我编写了一个 SSH 客户端来连接到网络设备,一旦运行命令超过 25 秒,我就通过“选择”设置超时。我注意到一些设备有另一个 IOS,一旦超时被触发并导致 goroutinge 泄漏,它就无法通过 Close() 方法删除与它们的 SSH session 。我需要跟上客户端并断开 session 以准备好下一个命令。看起来 goroutine 在那个时候不会永远终止!你们有什么想法吗?
go func() {
r <- s.Run(cmd)
}()
select {
case err := <-r:
return err
case <-time.After(time.Duration(timeout) * time.Second):
s.Close()
return fmt.Errorf("timeout after %d seconds", timeout)
}
通过堆分析,我看到了以下内容:
2.77GB 99.44% 99.44% 2.77GB 99.44% bytes.makeSlice
0 0% 99.44% 2.77GB 99.44% bytes.(*Buffer).ReadFrom
0 0% 99.44% 2.77GB 99.44% golang.org/x/crypto/ssh.(*Session).start.func1
0 0% 99.44% 2.77GB 99.44% golang.org/x/crypto/ssh.(*Session).stdout.func1
0 0% 99.44% 2.77GB 99.44% io.Copy
0 0% 99.44% 2.77GB 99.44% io.copyBuffer
0 0% 99.44% 2.78GB 99.93% runtime.goexit
例程 ========================/usr/local/go/src/runtime/asm_amd64.s 中的 runtime.goexit
0 2.78GB (flat, cum) 99.93% of Total
. . 1993: RET
. . 1994:
. . 1995:// The top-most function running on a goroutine
. . 1996:// returns to goexit+PCQuantum.
. . 1997:TEXT runtime·goexit(SB),NOSPLIT,$0-0
. 2.78GB 1998: BYTE $0x90 // NOP
. . 1999: CALL runtime·goexit1(SB) // does not return
. . 2000: // traceback from goexit1 must hit code range of goexit
. . 2001: BYTE $0x90 // NOP
. . 2002:
. . 2003:TEXT runtime·prefetcht0(SB),NOSPLIT,$0-8
最佳答案
channel r
阻止 Go 例程返回,因为它没有被清空。我已经编写了您代码的改编版本并插入了一个 WaitGroup 来演示问题:
func main() {
var wg sync.WaitGroup // This is only added for demonstration purposes
s := new(clientSession)
r := make(chan error)
go func(s *clientSession) {
wg.Add(1)
r <- s.Run()
wg.Done() // Will only be called after s.Run() is able to return
}(s)
fmt.Println("Client has been opened")
select {
case err := <-r:
fmt.Println(err)
case <-time.After(1 * time.Second):
s.Close()
fmt.Println("Timed out, closing")
}
wg.Wait() // Waits until wg.Done() is called.
fmt.Println("Main finished successfully")
}
Go Playground 似乎终止了程序,所以我创建了一个 gist带有完整的可运行代码。当我们运行
incorrect.go
:$ go run incorrect.go
Client has been opened
Timed out, closing
fatal error: all goroutines are asleep - deadlock!
....
那是因为我们的代码在
wg.Wait()
上死锁了线。这表明 wg.Done()
在 Go 例程中从未达到过。正如评论所指出的,缓冲 channel 可以在这里提供帮助。但前提是你不再关心错误,在调用
s.Close()
之后r := make(chan error, 1)
buffered.go
运行正常,但错误丢失:$ go run buffered.go
Client has been opened
Timed out, closing
Main finished successfully
另一种选择是精确地排空 channel 1 次:
select {
case err := <-r:
fmt.Println(err)
case <-time.After(1 * time.Second):
s.Close()
fmt.Println("Timed out, closing")
fmt.Println(<-r)
}
或者通过包装
select
在 for
循环(无缓冲 channel ):X:
for {
select {
case err := <-r:
fmt.Println(err)
break X // because we are in main(). Normally `return err`
case <-time.After(1 * time.Second):
s.Close()
fmt.Println("Timed out, closing")
}
}
当我们运行
drain.go
我们看到错误也打印出来:$ go run incorrect.go
Client has been opened
Timed out, closing
Run() closed
Main finished successfully
在现实世界中,一个人会运行多个 Go 程序。所以你会想在
for
上使用一些计数器。循环或进一步利用 WaitGroup 功能。
关于go - 强制关闭 SSH 客户端 session ,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/37040099/