func lockFcntl(name string) (io.Closer, error) {
fi, err := os.Stat(name)
if err == nil && fi.Size() > 0 {
return nil, fmt.Errorf("can't Lock file %q: has non-zero size", name)
}
f, err := os.Create(name)
if err != nil {
return nil, fmt.Errorf("Lock Create of %s failed: %v", name, err)
}
err = unix.FcntlFlock(f.Fd(), unix.F_SETLK, &unix.Flock_t{
Type: unix.F_WRLCK,
Whence: int16(os.SEEK_SET),
Start: 0,
Len: 0, // 0 means to lock the entire file.
Pid: 0, // only used by F_GETLK
})
if err != nil {
f.Close()
return nil, fmt.Errorf("Lock FcntlFlock of %s failed: %v", name, err)
}
return &unlocker{f: f, abs: name}, nil
}
// Acquire acquires a lock on a file for the duration of the process. This method
// is reentrant.
func Acquire(path string) error {
lock.Lock()
defer lock.Unlock()
var err error
if lockfile, err = os.OpenFile(path, os.O_RDWR|os.O_CREATE, 0600); err != nil {
return err
}
opts := unix.Flock_t{Type: unix.F_WRLCK}
if err := unix.FcntlFlock(lockfile.Fd(), unix.F_SETLKW, &opts); err != nil {
return err
}
return nil
}
// TestFcntlFlock tests whether the file locking structure matches
// the calling convention of each kernel.
func TestFcntlFlock(t *testing.T) {
name := filepath.Join(os.TempDir(), "TestFcntlFlock")
fd, err := unix.Open(name, unix.O_CREAT|unix.O_RDWR|unix.O_CLOEXEC, 0)
if err != nil {
t.Fatalf("Open failed: %v", err)
}
defer unix.Unlink(name)
defer unix.Close(fd)
flock := unix.Flock_t{
Type: unix.F_RDLCK,
Start: 0, Len: 0, Whence: 1,
}
if err := unix.FcntlFlock(uintptr(fd), unix.F_GETLK, &flock); err != nil {
t.Fatalf("FcntlFlock failed: %v", err)
}
}