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