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flock.go
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flock.go
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package flock
import (
"context"
"errors"
"fmt"
"os"
"path/filepath"
"strconv"
"time"
"golang.org/x/sys/unix"
)
var ErrLocked = errors.New("locked")
// Acquire a lock on the given path.
//
// The lock is released when the returned function is called.
func Acquire(ctx context.Context, path string, timeout time.Duration) (release func() error, err error) {
absPath, err := filepath.Abs(path)
if err != nil {
return nil, err
}
end := time.Now().Add(timeout)
for {
release, err := acquire(absPath)
if err == nil {
return release, nil
}
if !errors.Is(err, ErrLocked) {
return nil, fmt.Errorf("failed to acquire lock %s: %w", absPath, err)
}
if time.Now().After(end) {
pid, _ := os.ReadFile(absPath) //nolint:errcheck
return nil, fmt.Errorf("timed out acquiring lock %s, locked by pid %s: %w", absPath, pid, err)
}
select {
case <-ctx.Done():
return nil, ctx.Err()
case <-time.After(time.Second):
}
}
}
func acquire(path string) (release func() error, err error) {
pid := os.Getpid()
fd, err := unix.Open(path, unix.O_CREAT|unix.O_RDWR|unix.O_CLOEXEC|unix.O_SYNC, 0600)
if err != nil {
return nil, fmt.Errorf("open failed: %w", err)
}
err = unix.Flock(fd, unix.LOCK_EX|unix.LOCK_NB)
if err != nil {
_ = unix.Close(fd)
return nil, fmt.Errorf("%w: %w", ErrLocked, err)
}
_, err = unix.Write(fd, []byte(strconv.Itoa(pid)))
if err != nil {
return nil, fmt.Errorf("write failed: %w", err)
}
return func() error {
return errors.Join(unix.Flock(fd, unix.LOCK_UN), unix.Close(fd), os.Remove(path))
}, nil
}