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Example of gracefully shutting down and re-loading / restarting a Go app on SIGHUP retaining the same PID
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| // program | |
| package main | |
| import ( | |
| "fmt" | |
| "log" | |
| "os" | |
| "os/signal" | |
| "syscall" | |
| "time" | |
| ) | |
| func main() { | |
| // Compile and run this program and send SIGHUP. eg: pkill -9 go-graceful-reload | |
| fmt.Printf("Welcome: %s: pid is %d\n", os.Args, os.Getpid()) | |
| // Everything happens here. HTTP servers and other blocking calls, should | |
| // be invoked as goroutines. | |
| // srv := http.ListenAndServe() | |
| // This should be at the end of main(). | |
| cleanupWait := make(chan bool) | |
| <-awaitReload(cleanupWait, func() { | |
| // This callback can be used to gracefully close resources like | |
| // HTTP servers, DB connections etc. | |
| // srv.Close() | |
| fmt.Println("reloading!") | |
| // After closing everything, send the ready signal. | |
| cleanupWait <- true | |
| }) | |
| } | |
| func awaitReload(closerWait chan bool, closer func()) chan bool { | |
| // The blocking signal handler that main() waits on. | |
| out := make(chan bool) | |
| // Respawn a new process and exit the running one. syscall.Exec() retains | |
| // the original PID. | |
| respawn := func() { | |
| if err := syscall.Exec(os.Args[0], os.Args, os.Environ()); err != nil { | |
| log.Fatalf("error spawning process: %v", err) | |
| } | |
| os.Exit(0) | |
| } | |
| // Listen for reload signals. | |
| c := make(chan os.Signal, 1) | |
| signal.Notify(c, syscall.SIGHUP) | |
| go func() { | |
| for range c { | |
| log.Println("got reload signal. restarting ...") | |
| go closer() | |
| select { | |
| case <-closerWait: | |
| // Wait for the closer to finish. | |
| respawn() | |
| case <-time.After(time.Second * 3): | |
| // Or timeout and force close. | |
| respawn() | |
| } | |
| } | |
| }() | |
| return out | |
| } |
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