dir_other.go raw

   1  //go:build js || wasip1
   2  // +build js wasip1
   3  
   4  /*
   5   * SPDX-FileCopyrightText: © Hypermode Inc. <hello@hypermode.com>
   6   * SPDX-License-Identifier: Apache-2.0
   7   */
   8  
   9  package badger
  10  
  11  import (
  12  	"fmt"
  13  	"os"
  14  	"path/filepath"
  15  
  16  	"github.com/dgraph-io/badger/v4/y"
  17  )
  18  
  19  // directoryLockGuard holds a lock on a directory and a pid file inside.  The pid file isn't part
  20  // of the locking mechanism, it's just advisory.
  21  type directoryLockGuard struct {
  22  	// File handle on the directory, which we've flocked.
  23  	f *os.File
  24  	// The absolute path to our pid file.
  25  	path string
  26  	// Was this a shared lock for a read-only database?
  27  	readOnly bool
  28  }
  29  
  30  // acquireDirectoryLock gets a lock on the directory (using flock). If
  31  // this is not read-only, it will also write our pid to
  32  // dirPath/pidFileName for convenience.
  33  func acquireDirectoryLock(dirPath string, pidFileName string, readOnly bool) (
  34  	*directoryLockGuard, error) {
  35  	// Convert to absolute path so that Release still works even if we do an unbalanced
  36  	// chdir in the meantime.
  37  	absPidFilePath, err := filepath.Abs(filepath.Join(dirPath, pidFileName))
  38  	if err != nil {
  39  		return nil, y.Wrapf(err, "cannot get absolute path for pid lock file")
  40  	}
  41  	f, err := os.Open(dirPath)
  42  	if err != nil {
  43  		return nil, y.Wrapf(err, "cannot open directory %q", dirPath)
  44  	}
  45  
  46  	// NOTE: Here is where we would normally call flock.
  47  	// This is not supported in js / wasm, so skip it.
  48  
  49  	if !readOnly {
  50  		// Yes, we happily overwrite a pre-existing pid file.  We're the
  51  		// only read-write badger process using this directory.
  52  		err = os.WriteFile(absPidFilePath, []byte(fmt.Sprintf("%d\n", os.Getpid())), 0666)
  53  		if err != nil {
  54  			f.Close()
  55  			return nil, y.Wrapf(err,
  56  				"Cannot write pid file %q", absPidFilePath)
  57  		}
  58  	}
  59  
  60  	return &directoryLockGuard{f, absPidFilePath, readOnly}, nil
  61  }
  62  
  63  // Release deletes the pid file and releases our lock on the directory.
  64  func (guard *directoryLockGuard) release() error {
  65  	var err error
  66  	if !guard.readOnly {
  67  		// It's important that we remove the pid file first.
  68  		err = os.Remove(guard.path)
  69  	}
  70  
  71  	if closeErr := guard.f.Close(); err == nil {
  72  		err = closeErr
  73  	}
  74  	guard.path = ""
  75  	guard.f = nil
  76  
  77  	return err
  78  }
  79  
  80  // openDir opens a directory for syncing.
  81  func openDir(path string) (*os.File, error) { return os.Open(path) }
  82  
  83  // When you create or delete a file, you have to ensure the directory entry for the file is synced
  84  // in order to guarantee the file is visible (if the system crashes). (See the man page for fsync,
  85  // or see https://github.com/coreos/etcd/issues/6368 for an example.)
  86  func syncDir(dir string) error {
  87  	f, err := openDir(dir)
  88  	if err != nil {
  89  		return y.Wrapf(err, "While opening directory: %s.", dir)
  90  	}
  91  
  92  	err = f.Sync()
  93  	closeErr := f.Close()
  94  	if err != nil {
  95  		return y.Wrapf(err, "While syncing directory: %s.", dir)
  96  	}
  97  	return y.Wrapf(closeErr, "While closing directory: %s.", dir)
  98  }
  99