Add check for other instances

cmd/cameraSort/main.go → cmd/CNETCAM_sort/main.go

@@ -20,15 +20,24 @@ func init() {
 	log = logolang.NewLogger()
 	log.Level = logolang.LevelError
 
-	var verbose, version bool
+	var (
+		pidFile string
+		verbose, version bool
+	)
 	flag.StringVar(&from, "from", "", "Path to read the files")
 	flag.StringVar(&to, "to", "", "Path to put the files")
+	flag.StringVar(&pidFile, "pid", "/run/CNETCAM_sort.pid", "Path to pid file")
 	flag.BoolVar(&verbose, "verbose", false, "Verbose output")
 	flag.BoolVar(&verbose, "v", false, "Verbose output")
 	flag.BoolVar(&version, "version", false, "Print version and exit")
 	flag.BoolVar(&version, "V", false, "Print version and exit")
 	flag.Parse()
 
+	if err := utils.PID(pidFile); err != nil {
+		log.Criticalf("error checking for other instances: %s", err)
+		os.Exit(1)
+	}
+
 	if version {
 		fmt.Println(internal.Version)
 		os.Exit(0)

pkg/utils/cron.go

@@ -0,0 +1,10 @@
+package utils
+
+import "time"
+
+func ExecuteEvery(f func(), d time.Duration) {
+	wait := time.NewTicker(d).C
+	for range wait {
+		f()
+	}
+}

pkg/utils/process.go

@@ -0,0 +1,97 @@
+package utils
+
+import (
+	"errors"
+	"fmt"
+	"golang.org/x/sys/unix"
+	"io/ioutil"
+	"os"
+	"strconv"
+)
+
+// errCleanPID is the error returned when the
+var errEmpty = errors.New("empty file")
+
+// PID checks if other instances of the program is running (using the path to the .pid file provided).
+// If so, it will exit with error code 0
+// If not, it will create/update the .pid file provided
+func PID(path string) error {
+	// Read pid from path
+	pid, err := readPID(path)
+	if err != nil {
+		// Create/overwrite pid file if it doesn't exist or is empty.
+		if errors.Is(err, os.ErrNotExist) || errors.Is(err, errEmpty) {
+			return createPID(path)
+		}
+
+		// If other error, return
+		return err
+	}
+
+	// Check if process with the pid provided exists
+	exists, err := processExists(pid)
+	if err != nil {
+		return err
+	}
+
+	// Exit if exists, create pid file otherwise
+	if exists {
+		os.Exit(1)
+	}
+	return createPID(path)
+}
+
+// createPID creates/overwrites the path provided with a file that contains this program's PID
+func createPID(path string) error {
+	f, err := os.Create(path)
+	if err != nil {
+		return fmt.Errorf("cannot create pid file: %w", err)
+	}
+	defer f.Close()
+
+	if _, err = f.WriteString(strconv.Itoa(os.Getpid()) + "\n"); err != nil {
+		return fmt.Errorf("cannot write pid file: %w", err)
+	}
+
+	if err = f.Close(); err != nil {
+		return fmt.Errorf("error closing pid file: %w", err)
+	}
+	return nil
+}
+
+// readPID reads the pid from the path provided
+func readPID(path string) (int, error) {
+	// Read data from path
+	data, err := ioutil.ReadFile(path)
+	if err != nil {
+		return 0, fmt.Errorf("error reading pid file: %w", err)
+	}
+
+	// Check it's not empty
+	if len(data) == 0 {
+		return 0, errEmpty
+	}
+
+	// Remove last linebreak
+	if data[len(data)-1] == '\n' {
+		data = data[:len(data)-1]
+	}
+
+	// Get the pid
+	pid, err := strconv.Atoi(string(data))
+	if err != nil {
+		return 0, fmt.Errorf("error parsing PID: %w", err)
+	}
+	return pid, nil
+}
+
+// processExists checks if a process with the pid provided exists
+func processExists(pid int) (bool, error) {
+	if err := unix.Kill(pid, unix.Signal(0)); err != nil {
+		if !errors.Is(err, unix.ESRCH) {
+			return false, fmt.Errorf("error checking existence of process with pid %d: %w", pid, err)
+		}
+		return false, nil
+	}
+	return true, nil
+}