Replace per-file locking with single PID lock file

File locks have a multitude of problems that make them hard to use
correctly. As they are just advisory, they are only meaningful to
prevent accidents like running the same process twice.
A simple PID file lock works reliably in those cases and is simpler.

block.go

@@ -7,7 +7,6 @@ import (
 	"path/filepath"
 	"sort"
 
-	"github.com/coreos/etcd/pkg/fileutil"
 	"github.com/pkg/errors"
 )
 
@@ -175,14 +174,12 @@ func indexFileName(path string) string {
 }
 
 type mmapFile struct {
-	f *fileutil.LockedFile
+	f *os.File
 	b []byte
 }
 
 func openMmapFile(path string) (*mmapFile, error) {
-	// We have to open the file in RDWR for the lock to work with fileutil.
-	// TODO(fabxc): use own flock call that supports multi-reader.
-	f, err := fileutil.TryLockFile(path, os.O_RDWR, 0666)
+	f, err := os.Open(path)
 	if err != nil {
 		return nil, errors.Wrap(err, "try lock file")
 	}
@@ -191,7 +188,7 @@ func openMmapFile(path string) (*mmapFile, error) {
 		return nil, errors.Wrap(err, "stat")
 	}
 
-	b, err := mmap(f.File, int(info.Size()))
+	b, err := mmap(f, int(info.Size()))
 	if err != nil {
 		return nil, errors.Wrap(err, "mmap")
 	}

compact.go

@@ -167,11 +167,11 @@ func (c *compactor) compact(dir string, blocks ...Block) (err error) {
 		return err
 	}
 
-	chunkf, err := fileutil.LockFile(chunksFileName(dir), os.O_WRONLY|os.O_CREATE, 0666)
+	chunkf, err := os.OpenFile(chunksFileName(dir), os.O_WRONLY|os.O_CREATE, 0666)
 	if err != nil {
 		return errors.Wrap(err, "create chunk file")
 	}
-	indexf, err := fileutil.LockFile(indexFileName(dir), os.O_WRONLY|os.O_CREATE, 0666)
+	indexf, err := os.OpenFile(indexFileName(dir), os.O_WRONLY|os.O_CREATE, 0666)
 	if err != nil {
 		return errors.Wrap(err, "create index file")
 	}
@@ -189,10 +189,10 @@ func (c *compactor) compact(dir string, blocks ...Block) (err error) {
 	if err = indexw.Close(); err != nil {
 		return errors.Wrap(err, "close index writer")
 	}
-	if err = fileutil.Fsync(chunkf.File); err != nil {
+	if err = fileutil.Fsync(chunkf); err != nil {
 		return errors.Wrap(err, "fsync chunk file")
 	}
-	if err = fileutil.Fsync(indexf.File); err != nil {
+	if err = fileutil.Fsync(indexf); err != nil {
 		return errors.Wrap(err, "fsync index file")
 	}
 	if err = chunkf.Close(); err != nil {

db.go

@@ -21,6 +21,7 @@ import (
 	"github.com/coreos/etcd/pkg/fileutil"
 	"github.com/fabxc/tsdb/labels"
 	"github.com/go-kit/kit/log"
+	"github.com/nightlyone/lockfile"
 	"github.com/pkg/errors"
 	"github.com/prometheus/client_golang/prometheus"
 )
@@ -86,6 +87,7 @@ const sep = '\xff'
 // a hashed partition of a seriedb.
 type DB struct {
 	dir     string
+	lockf   lockfile.Lockfile
 	logger  log.Logger
 	metrics *dbMetrics
 	opts    *Options
@@ -130,11 +132,22 @@ func newDBMetrics(r prometheus.Registerer) *dbMetrics {
 
 // Open returns a new DB in the given directory.
 func Open(dir string, logger log.Logger, opts *Options) (db *DB, err error) {
-	if !fileutil.Exist(dir) {
-		if err := os.MkdirAll(dir, 0777); err != nil {
-			return nil, err
-		}
+	if err := os.MkdirAll(dir, 0777); err != nil {
+		return nil, err
 	}
+
+	absdir, err := filepath.Abs(dir)
+	if err != nil {
+		return nil, err
+	}
+	lockf, err := lockfile.New(filepath.Join(absdir, "lock"))
+	if err != nil {
+		return nil, err
+	}
+	if err := lockf.TryLock(); err != nil {
+		return nil, errors.Wrapf(err, "open DB in %s", dir)
+	}
+
 	// var r prometheus.Registerer
 	r := prometheus.DefaultRegisterer
 
@@ -147,6 +160,7 @@ func Open(dir string, logger log.Logger, opts *Options) (db *DB, err error) {
 
 	db = &DB{
 		dir:      dir,
+		lockf:    lockf,
 		logger:   logger,
 		metrics:  newDBMetrics(r),
 		opts:     opts,
@@ -374,6 +388,8 @@ func (db *DB) Close() error {
 		merr.Add(hb.Close())
 	}
 
+	merr.Add(db.lockf.Unlock())
+
 	return merr.Err()
 }
 

wal.go

@@ -42,7 +42,7 @@ type WAL struct {
 	mtx sync.Mutex
 
 	dirFile *os.File
-	files   []*fileutil.LockedFile
+	files   []*os.File
 
 	logger        log.Logger
 	flushInterval time.Duration
@@ -128,19 +128,19 @@ func (w *WAL) initSegments() error {
 	}
 	if len(fns) > 1 {
 		for _, fn := range fns[:len(fns)-1] {
-			lf, err := fileutil.TryLockFile(fn, os.O_RDONLY, 0666)
+			f, err := os.Open(fn)
 			if err != nil {
 				return err
 			}
-			w.files = append(w.files, lf)
+			w.files = append(w.files, f)
 		}
 	}
 	// The most recent WAL file is the one we have to keep appending to.
-	lf, err := fileutil.TryLockFile(fns[len(fns)-1], os.O_RDWR, 0666)
+	f, err := os.OpenFile(fns[len(fns)-1], os.O_RDWR, 0666)
 	if err != nil {
 		return err
 	}
-	w.files = append(w.files, lf)
+	w.files = append(w.files, f)
 
 	// Consume and validate meta headers.
 	for _, f := range w.files {
@@ -187,11 +187,11 @@ func (w *WAL) cut() error {
 	if err != nil {
 		return err
 	}
-	f, err := fileutil.LockFile(p, os.O_RDWR|os.O_CREATE, 0666)
+	f, err := os.Create(p)
 	if err != nil {
 		return err
 	}
-	if err = fileutil.Preallocate(f.File, w.segmentSize, true); err != nil {
+	if err = fileutil.Preallocate(f, w.segmentSize, true); err != nil {
 		return err
 	}
 	if err = w.dirFile.Sync(); err != nil {
@@ -214,7 +214,7 @@ func (w *WAL) cut() error {
 	return nil
 }
 
-func (w *WAL) tail() *fileutil.LockedFile {
+func (w *WAL) tail() *os.File {
 	if len(w.files) == 0 {
 		return nil
 	}
@@ -235,7 +235,7 @@ func (w *WAL) sync() error {
 	if err := w.cur.Flush(); err != nil {
 		return err
 	}
-	return fileutil.Fdatasync(w.tail().File)
+	return fileutil.Fdatasync(w.tail())
 }
 
 func (w *WAL) run(interval time.Duration) {