a go example for waiting file lock, based on github.com/lomik/go-carbon

main.go

package main

import (
	"flag"
	"fmt"
	"log"
	"os"
	"syscall"
	"time"
)

var pid = os.Getpid()

func main() {
	lockFilename := flag.String("lock", "my.lock", "lock file path")
	flag.Parse()

	log.SetFlags(log.LstdFlags | log.Lmicroseconds)

	err := run(*lockFilename)
	if err != nil {
		log.Fatalf("got error in run, pid=%d, err=%v", pid, err)
	}
}

func run(lockFilename string) error {
	file, err := openWithLock(lockFilename)
	if err != nil {
		if !os.IsNotExist(err) {
			return fmt.Errorf("failed to open lock file=%s, err=%v", lockFilename, err)
		}

		file, err = createWithLock(lockFilename)
		if err != nil {
			return fmt.Errorf("failed to create lock file=%s, err=%v", lockFilename, err)
		}
	}
	defer func() {
		log.Printf("flock-example closing file=%s, now take some sleep, pid=%d", lockFilename, pid)
		file.Close()
	}()

	err = writeSomeLog(file)
	if err != nil {
		return fmt.Errorf("failed to write to lock file=%s, err=%v", lockFilename, err)
	}

	return nil
}

func openWithLock(lockFilename string) (*os.File, error) {
	log.Printf("flock-example try opening file=%s, pid=%d", lockFilename, pid)
	file, err := os.OpenFile(lockFilename, os.O_RDWR|os.O_APPEND, 0666)
	if err != nil {
		return nil, err
	}

	log.Printf("flock-example try locking opened file=%s, pid=%d", lockFilename, pid)
	err = syscall.Flock(int(file.Fd()), syscall.LOCK_EX)
	if err != nil {
		return nil, err
	}
	log.Printf("flock-example got lock for opened file=%s, pid=%d", lockFilename, pid)

	return file, nil
}

func createWithLock(lockFilename string) (*os.File, error) {
	log.Printf("flock-example check file exists before creating file=%s, pid=%d", lockFilename, pid)
	_, err := os.Stat(lockFilename)
	if err == nil {
		return nil, os.ErrExist
	}

	log.Printf("flock-example try creating file=%s, pid=%d", lockFilename, pid)
	file, err := os.Create(lockFilename)
	if err != nil {
		return nil, err
	}

	log.Printf("flock-example try locking created file=%s, pid=%d", lockFilename, pid)
	err = syscall.Flock(int(file.Fd()), syscall.LOCK_EX)
	if err != nil {
		return nil, err
	}
	log.Printf("flock-example got lock for created file=%s, pid=%d", lockFilename, pid)

	return file, nil
}

func writeSomeLog(file *os.File) error {
	// Emulate some work.
	time.Sleep(5 * time.Second)

	_, err := fmt.Fprintf(file, "%s write some log from pid=%d\n", time.Now().Format(time.RFC3339Nano), pid)
	return err
}

The original code:

• store
• OpenWithOptions
• CreateWithOptions