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file_lock.go
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file_lock.go
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/*
* Copyright 2020 The Dragonfly Authors
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package fileutils
import (
"os"
"syscall"
"github.com/pkg/errors"
)
// FileLock defines a file lock implemented by syscall.Flock.
// Locks created by flock() are associated with an open file
// description. This means that duplicate file
// descriptors (created by, for example, fork or dup) refer to
// the same lock, and this lock may be modified or released using
// any of these file descriptors. Furthermore, the lock is released
// either by an explicit LOCK_UN operation on any of these duplicate
// file descriptors, or when all such file descriptors have been closed.
type FileLock struct {
fileName string
ofile *os.File
}
func NewFileLock(path string) (*FileLock, error) {
ofile, err := OpenFile(path, syscall.O_CREAT|syscall.O_RDONLY, 0644)
if err != nil {
return nil, err
}
return &FileLock{
fileName: path,
ofile: ofile,
}, nil
}
func (locker *FileLock) Lock() error {
if locker.ofile == nil {
return errors.Errorf("lock file %s: not open", locker.fileName)
}
if err := syscall.Flock(int(locker.ofile.Fd()), syscall.LOCK_EX); err != nil {
return errors.Wrapf(err, "failed to lock file %s", locker.fileName)
}
return nil
}
func (locker *FileLock) TryLock() error {
if locker.ofile == nil {
return errors.Errorf("try lock file %s: not open", locker.fileName)
}
return syscall.Flock(int(locker.ofile.Fd()), syscall.LOCK_NB|syscall.LOCK_EX)
}
func (locker *FileLock) Unlock() error {
if locker.ofile == nil {
return nil
}
if err := syscall.Flock(int(locker.ofile.Fd()), syscall.LOCK_UN); err != nil {
return errors.Wrapf(err, "failed to unlock file %s", locker.fileName)
}
return nil
}