101 lines
2.9 KiB
Go
101 lines
2.9 KiB
Go
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// +build !windows
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/*
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* Copyright 2017 Dgraph Labs, Inc. and Contributors
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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 badger
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import (
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"fmt"
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"io/ioutil"
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"os"
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"path/filepath"
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"github.com/pkg/errors"
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"golang.org/x/sys/unix"
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)
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// directoryLockGuard holds a lock on a directory and a pid file inside. The pid file isn't part
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// of the locking mechanism, it's just advisory.
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type directoryLockGuard struct {
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// File handle on the directory, which we've flocked.
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f *os.File
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// The absolute path to our pid file.
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path string
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// Was this a shared lock for a read-only database?
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readOnly bool
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}
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// acquireDirectoryLock gets a lock on the directory (using flock). If
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// this is not read-only, it will also write our pid to
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// dirPath/pidFileName for convenience.
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func acquireDirectoryLock(dirPath string, pidFileName string, readOnly bool) (*directoryLockGuard, error) {
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// Convert to absolute path so that Release still works even if we do an unbalanced
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// chdir in the meantime.
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absPidFilePath, err := filepath.Abs(filepath.Join(dirPath, pidFileName))
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if err != nil {
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return nil, errors.Wrap(err, "cannot get absolute path for pid lock file")
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}
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f, err := os.Open(dirPath)
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if err != nil {
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return nil, errors.Wrapf(err, "cannot open directory %q", dirPath)
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}
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opts := unix.LOCK_EX | unix.LOCK_NB
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if readOnly {
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opts = unix.LOCK_SH | unix.LOCK_NB
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}
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err = unix.Flock(int(f.Fd()), opts)
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if err != nil {
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f.Close()
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return nil, errors.Wrapf(err,
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"Cannot acquire directory lock on %q. Another process is using this Badger database.",
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dirPath)
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}
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if !readOnly {
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// Yes, we happily overwrite a pre-existing pid file. We're the
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// only read-write badger process using this directory.
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err = ioutil.WriteFile(absPidFilePath, []byte(fmt.Sprintf("%d\n", os.Getpid())), 0666)
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if err != nil {
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f.Close()
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return nil, errors.Wrapf(err,
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"Cannot write pid file %q", absPidFilePath)
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}
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}
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return &directoryLockGuard{f, absPidFilePath, readOnly}, nil
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}
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// Release deletes the pid file and releases our lock on the directory.
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func (guard *directoryLockGuard) release() error {
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var err error
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if !guard.readOnly {
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// It's important that we remove the pid file first.
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err = os.Remove(guard.path)
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}
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if closeErr := guard.f.Close(); err == nil {
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err = closeErr
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}
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guard.path = ""
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guard.f = nil
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return err
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}
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// openDir opens a directory for syncing.
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func openDir(path string) (*os.File, error) { return os.Open(path) }
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