How to implement the hot switch function of Go program-Golang-php.cn

How to implement the hot switch function of Go program more coolly

Release： 2023-07-21 12:00:03

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During development, we often have the need for thermal switches, that is, specific functions can be turned on or off at appropriate times while the program is running. For example, pprof sampling used in performance analysis is a typical thermal switch. This article discusses how to make this thermal switch cooler.

Before introducing the new solution, let’s review how pprof is done in the Go program.

Interface call

Performance sampling of the program may affect its service capabilities. Therefore, online sampling is generally performed within a specified small time range and requires effective switch control.

In order to achieve this, we generally introduce the net/http/pprof package (its init function is bound to the routing function function) into the code. The sampling function is turned on when externally accessing the HTTP service of the specified port. After the sampling time is over, the collection is turned off.

The implementation code is as follows

package main

import (
 "net/http"
 _ "net/http/pprof"
)

func main() {
 go func() {
  _ = http.ListenAndServe(":8080", nil)
 }()
 ...
}

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Of course there is no problem with this approach. We can learn it and make other switch functions into HTTP services. But, is there any other cooler way?

信号通知

在信号处理与 Go 程序的优雅退出一文中，我们谈论过信号机制，它用以向应用程序发送某种事件通知。

我们可以将基于接口触发的方式改为信号通知。

首先，构造采样功能函数（对应于 net/http/pprof 包下 init 函数中绑定的路由功能函数）。

func RegisterSignalForProfiling(sig os.Signal) {
 ch := make(chan os.Signal)
 started := false
 signal.Notify(ch, sig)

 go func() {
  var memoryProfile, cpuProfile, traceProfile *os.File
  for range ch {
   if started {
    pprof.StopCPUProfile()
    trace.Stop()
    pprof.WriteHeapProfile(memoryProfile)
    memoryProfile.Close()
    cpuProfile.Close()
    traceProfile.Close()
    started = false
   } else {
    cpuProfile, _ = os.Create("cpu.pprof")
    memoryProfile, _ = os.Create("memory.pprof")
    traceProfile, _ = os.Create("runtime.trace")
    pprof.StartCPUProfile(cpuProfile)
    trace.Start(traceProfile)
    started = true
   }
  }
 }()
}

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在上述函数中，我们定义了接收信号通道ch，通过signal.Notify(ch, sig)将指定的通知信号sig与ch进行绑定。for range ch 将阻塞等待外部信号sig，随着sig信号的到来，交替进入开启或关闭采样的逻辑。

在main函数中，就可以这样替代http.ListenAndServe(":8080", nil)了。

package main

import (
  "syscall"
  ...
)

func main() {
  RegisterSignalForProfiling(syscall.Signal(31))
 ...
}

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在 linux 系统，可以通过kill -signal_number pid命令向程序发送指定信号。

如上代码所示，我们硬编码指定的采样开关信号值是 31。因此，当程序运行起来后，我们在控制台输入kill -31 pid 命令，即可开启采样，再次输入kill -31 pid命令，就关闭了采样。

依葫芦画瓢，我们再来一个打印 goroutine 堆栈信息的热开关函数，是不是很酷？

func RegisterSignalForPrintStack(sig os.Signal) {
 ch := make(chan os.Signal)
 signal.Notify(ch, sig)

 go func() {
  for range ch {
   buffer := make([]byte, 1024*1024*4)
   runtime.Stack(buffer, true)
   fmt.Println(string(buffer))
  }
 }()
}

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总结

热开关是一个很简单常用的功能，无非是选择何种触发与等待方式。基于接口的调用更适合于远程控制，基于信号则便于本地控制。

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