// flock acquires an advisory lock on a file descriptor.
func flock(f *os.File, exclusive bool, timeout time.Duration) error {
var t time.Time
for {
// If we're beyond our timeout then return an error.
// This can only occur after we've attempted a flock once.
if t.IsZero() {
t = time.Now()
} else if timeout > 0 && time.Since(t) > timeout {
return ErrTimeout
}
var lock syscall.Flock_t
lock.Start = 0
lock.Len = 0
lock.Pid = 0
lock.Whence = 0
lock.Pid = 0
if exclusive {
lock.Type = syscall.F_WRLCK
} else {
lock.Type = syscall.F_RDLCK
}
err := syscall.FcntlFlock(f.Fd(), syscall.F_SETLK, &lock)
if err == nil {
return nil
} else if err != syscall.EAGAIN {
return err
}
// Wait for a bit and try again.
time.Sleep(50 * time.Millisecond)
}
}
// funlock releases an advisory lock on a file descriptor.
func funlock(f *os.File) error {
var lock syscall.Flock_t
lock.Start = 0
lock.Len = 0
lock.Type = syscall.F_UNLCK
lock.Whence = 0
return syscall.FcntlFlock(uintptr(f.Fd()), syscall.F_SETLK, &lock)
}
// Lock acquires exclusivity on the lock without blocking
func (l *lock) Lock() error {
var lock syscall.Flock_t
lock.Start = 0
lock.Len = 0
lock.Type = syscall.F_WRLCK
lock.Whence = 0
lock.Pid = 0
return syscall.FcntlFlock(uintptr(l.fd), syscall.F_SETLK, &lock)
}
// Unlock unlocks the lock
func (l *lock) Unlock() error {
var lock syscall.Flock_t
lock.Start = 0
lock.Len = 0
lock.Type = syscall.F_UNLCK
lock.Whence = 0
err := syscall.FcntlFlock(uintptr(l.fd), syscall.F_SETLK, &lock)
if err != nil && err == syscall.EAGAIN {
return ErrLocked
}
return err
}
func LockFile(path string, flag int, perm os.FileMode) (*LockedFile, error) {
var lock syscall.Flock_t
lock.Start = 0
lock.Len = 0
lock.Pid = 0
lock.Type = syscall.F_WRLCK
lock.Whence = 0
f, err := os.OpenFile(path, flag, perm)
if err != nil {
return nil, err
}
if err = syscall.FcntlFlock(f.Fd(), syscall.F_SETLKW, &lock); err != nil {
f.Close()
return nil, err
}
return &LockedFile{f}, nil
}