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