1 //go:build linux || darwin || freebsd || openbsd || netbsd || dragonfly 2 // +build linux darwin freebsd openbsd netbsd dragonfly 3 4 /* 5 Copyright 2016 The Kubernetes Authors. 6 7 Licensed under the Apache License, Version 2.0 (the "License"); 8 you may not use this file except in compliance with the License. 9 You may obtain a copy of the License at 10 11 http://www.apache.org/licenses/LICENSE-2.0 12 13 Unless required by applicable law or agreed to in writing, software 14 distributed under the License is distributed on an "AS IS" BASIS, 15 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 16 See the License for the specific language governing permissions and 17 limitations under the License. 18 */ 19 20 package flock 21 22 import ( 23 "errors" 24 "fmt" 25 "os" 26 27 "golang.org/x/sys/unix" 28 ) 29 30 // Acquire acquires a lock on a file for the duration of the process. This method 31 // is reentrant. 32 func Acquire(path string) error { 33 fd, err := unix.Open(path, unix.O_CREAT|unix.O_RDWR|unix.O_CLOEXEC, 0600) 34 if err != nil { 35 if errors.Is(err, os.ErrExist) { 36 return fmt.Errorf("cannot lock file %q: %w", path, ErrAlreadyLocked) 37 } 38 return err 39 } 40 41 // We don't need to close the fd since we should hold 42 // it until the process exits. 43 err = unix.Flock(fd, unix.LOCK_NB|unix.LOCK_EX) 44 if errors.Is(err, unix.EWOULDBLOCK) { // This condition requires LOCK_NB. 45 return fmt.Errorf("cannot lock file %q: %w", path, ErrAlreadyLocked) 46 } 47 return err 48 } 49