impl_flock.go

// Copyright 2016 Canonical Ltd.
// Licensed under the LGPLv3, see LICENCE file for details.

// +build !windows,!linux

package mutex

import (
	"os"
	"syscall"

	"github.com/juju/errors"
)

type impl struct {
	fd int
}

func acquire(name string) (Releaser, error) {
	fd, err := syscall.Open(flockName(name), syscall.O_CREAT|syscall.O_RDONLY, 0600)
	if err != nil {
		return nil, errors.Trace(err)
	}

	err = syscall.Flock(fd, syscall.LOCK_EX|syscall.LOCK_NB)
	if err != nil {
		syscall.Close(fd)

		if err == syscall.EWOULDBLOCK {
			return nil, errors.Trace(ErrLocked)
		}
		return nil, errors.Trace(err)
	}

	return &impl{fd: fd}, nil
}

// Release implements Releaser.
func (i *impl) Release() error {
	return syscall.Close(i.fd)
}

func flockName(name string) string {
	currentUser := os.Getenv("USER")
	if currentUser == "" {
		currentUser = "client"
	}
	return "/tmp/juju-" + currentUser + "-" + name
}