Golang Flock_t.Pid方法代码示例

// 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)
	}
}

// TryLock acquires exclusivity on the lock without blocking
func (l *lock) TryLock() error {
	var lock syscall.Flock_t
	lock.Start = 0
	lock.Len = 0
	lock.Pid = 0
	lock.Type = syscall.F_WRLCK
	lock.Whence = 0
	lock.Pid = 0
	err := syscall.FcntlFlock(uintptr(l.fd), syscall.F_SETLK, &lock)
	if err != nil && err == syscall.EAGAIN {
		return ErrLocked
	}
	return err
}

// 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)
}

func TryLockFile(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
	lock.Pid = 0
	f, err := os.OpenFile(path, flag, perm)
	if err != nil {
		return nil, err
	}
	if err := syscall.FcntlFlock(f.Fd(), syscall.F_SETLK, &lock); err != nil {
		f.Close()
		if err == syscall.EAGAIN {
			err = ErrLocked
		}
		return nil, err
	}
	return &LockedFile{f}, nil
}

// TestFcntlFlock tests whether the file locking structure matches
// the calling convention of each kernel.
// On some Linux systems, glibc uses another set of values for the
// commands and translates them to the correct value that the kernel
// expects just before the actual fcntl syscall. As Go uses raw
// syscalls directly, it must use the real value, not the glibc value.
// Thus this test also verifies that the Flock_t structure can be
// roundtripped with F_SETLK and F_GETLK.
func TestFcntlFlock(t *testing.T) {
	if runtime.GOOS == "darwin" && (runtime.GOARCH == "arm" || runtime.GOARCH == "arm64") {
		t.Skip("skipping; no child processes allowed on iOS")
	}
	flock := syscall.Flock_t{
		Type:  syscall.F_WRLCK,
		Start: 31415, Len: 271828, Whence: 1,
	}
	if os.Getenv("GO_WANT_HELPER_PROCESS") == "" {
		// parent
		name := filepath.Join(os.TempDir(), "TestFcntlFlock")
		fd, err := syscall.Open(name, syscall.O_CREAT|syscall.O_RDWR|syscall.O_CLOEXEC, 0)
		if err != nil {
			t.Fatalf("Open failed: %v", err)
		}
		defer syscall.Unlink(name)
		defer syscall.Close(fd)
		if err := syscall.Ftruncate(fd, 1<<20); err != nil {
			t.Fatalf("Ftruncate(1<<20) failed: %v", err)
		}
		if err := syscall.FcntlFlock(uintptr(fd), syscall.F_SETLK, &flock); err != nil {
			t.Fatalf("FcntlFlock(F_SETLK) failed: %v", err)
		}
		cmd := exec.Command(os.Args[0], "-test.run=^TestFcntlFlock$")
		cmd.Env = append(os.Environ(), "GO_WANT_HELPER_PROCESS=1")
		cmd.ExtraFiles = []*os.File{os.NewFile(uintptr(fd), name)}
		out, err := cmd.CombinedOutput()
		if len(out) > 0 || err != nil {
			t.Fatalf("child process: %q, %v", out, err)
		}
	} else {
		// child
		got := flock
		// make sure the child lock is conflicting with the parent lock
		got.Start--
		got.Len++
		if err := syscall.FcntlFlock(3, syscall.F_GETLK, &got); err != nil {
			t.Fatalf("FcntlFlock(F_GETLK) failed: %v", err)
		}
		flock.Pid = int32(syscall.Getppid())
		// Linux kernel always set Whence to 0
		flock.Whence = 0
		if got.Type == flock.Type && got.Start == flock.Start && got.Len == flock.Len && got.Pid == flock.Pid && got.Whence == flock.Whence {
			os.Exit(0)
		}
		t.Fatalf("FcntlFlock got %v, want %v", got, flock)
	}
}