Ensure only a single instance of after-lock runs at a time

cmd/after-lock/after-lock.go

@@ -2,19 +2,50 @@ package main
 
 import (
 	"after-lock/afterlock"
+	"after-lock/lockfile"
+	"fmt"
+	"runtime/debug"
+	"os"
 )
 
 const (
 	initialDelay = 3
 	loopDelay = 6
 	keyboardDeviceNode = "/dev/input/by-id/usb-Dell_Dell_USB_Entry_Keyboard-event-kbd"
+	lockfilePath = "/tmp/after-lock.lock"
+	printStackTraces = false
 )
 
 
 func main() {
+	defer handleErrors()
+
+	lock := grabExclusiveProcessLock()
+	defer lock.Unlock()
+
 	al := afterlock.New(keyboardDeviceNode)
 	al.InitialDelay = initialDelay
 	al.LoopDelay = loopDelay
 
 	al.Start()
+}
+
+func handleErrors() {
+	if err := recover(); err != nil {
+		fmt.Printf("Crashed with unexpected error: %v!\n", err)
+		if printStackTraces {
+			fmt.Printf("Stack trace:\n\n")
+			debug.PrintStack()
+		}
+		os.Exit(1)
+	}
+}
+
+func grabExclusiveProcessLock() *lockfile.Lockfile {
+	lf := lockfile.New(lockfilePath)
+	err := lf.Lock()
+	if err != nil {
+		panic(err)
+	}
+	return lf
 }