gistfile1.go

package storage

import (
	"golang.org/x/sys/unix"
	"os"
	"path/filepath"
)

// UserdirLock maintains a lock on a user directory.
type UserdirLock struct {
	file *os.File
}

// NewUserdirLock creates a new unlocked user directory lock.
func NewUserdirLock(userdir string) (*UserdirLock, error) {
	path := filepath.Join(userdir, "lock")
	file, err := os.OpenFile(path, os.O_CREATE, 0644)
	if err != nil {
		return nil, err
	}
	return &UserdirLock{file: file}, nil
}

// NewLockedUserdirLock creates a new locked user directory lock.
func NewLockedUserdirLock(userdir string) (*UserdirLock, error) {
	lock, err := NewUserdirLock(userdir)
	if err != nil {
		return nil, err
	}
	if err := lock.Lock(); err != nil {
		lock.Close()
		return nil, err
	}
	return lock, nil
}

// Close closes the user directory lock, but does not unlock it.
func (lock *UserdirLock) Close() error {
	return lock.file.Close()
}

// Lock locks the user directory. If the user directory is already locked, Lock
// will wait until it is unlocked.
func (lock *UserdirLock) Lock() error {
	return unix.Flock(int(lock.file.Fd()), unix.LOCK_EX)
}

// Unlock unlocks the user directory. If the user directory is already unlocked
// the behavior is undefined.
func (lock *UserdirLock) Unlock() error {
	return unix.Flock(int(lock.file.Fd()), unix.LOCK_UN)
}

// Unlock unlocks the user directory and closes the lock. If the user directory
// is already unlocked the behavior is undefined.
func (lock *UserdirLock) UnlockAndClose() error {
	if err := lock.Unlock(); err != nil {
		return err
	}
	return lock.Close()
}