Remove fsrepo Datastore refcounting

repo.Once now does refcounts on a whole Repo level, returning the same
pointer to multiple Openers. This removes the need for the weird model
of separate FSRepo instances pointing to the same underlying storage,
and the races caused by that.

repo/fsrepo/fsrepo.go

@@ -46,11 +46,6 @@ var (
 	// change the repo's state, the package lock does not need to be acquired.
 	openersCounter *counter.Openers
 
-	// protects dsOpenersCounter and datastores
-	dsLock           sync.Mutex
-	dsOpenersCounter *counter.Openers
-	datastores       map[string]ds2.ThreadSafeDatastoreCloser
-
 	// onlyOne keeps track of open FSRepo instances.
 	//
 	// TODO: once command Context / Repo integration is cleaned up,
@@ -69,9 +64,6 @@ var (
 func init() {
 	openersCounter = counter.NewOpenersCounter()
 	lockfiles = make(map[string]io.Closer)
-
-	dsOpenersCounter = counter.NewOpenersCounter()
-	datastores = make(map[string]ds2.ThreadSafeDatastoreCloser)
 }
 
 // FSRepo represents an IPFS FileSystem Repo. It is safe for use by multiple
@@ -254,32 +246,14 @@ func (r *FSRepo) openConfig() error {
 
 // openDatastore returns an error if the config file is not present.
 func (r *FSRepo) openDatastore() error {
-	dsLock.Lock()
-	defer dsLock.Unlock()
-
 	dsPath := path.Join(r.path, defaultDataStoreDirectory)
-
-	// if no other goroutines have the datastore Open, initialize it and assign
-	// it to the package-scoped map for the goroutines that follow.
-	if dsOpenersCounter.NumOpeners(dsPath) == 0 {
-		ds, err := levelds.NewDatastore(dsPath, &levelds.Options{
-			Compression: ldbopts.NoCompression,
-		})
-		if err != nil {
-			return debugerror.New("unable to open leveldb datastore")
-		}
-		datastores[dsPath] = ds
-	}
-
-	// get the datastore from the package-scoped map and record self as an
-	// opener.
-	ds, dsIsPresent := datastores[dsPath]
-	if !dsIsPresent {
-		// This indicates a programmer error has occurred.
-		return errors.New("datastore should be available, but it isn't")
+	ds, err := levelds.NewDatastore(dsPath, &levelds.Options{
+		Compression: ldbopts.NoCompression,
+	})
+	if err != nil {
+		return debugerror.New("unable to open leveldb datastore")
 	}
 	r.ds = ds
-	dsOpenersCounter.AddOpener(dsPath) // only after success
 	return nil
 }
 
@@ -295,24 +269,6 @@ func configureEventLoggerAtRepoPath(c *config.Config, repoPath string) {
 	eventlog.Configure(eventlog.OutputRotatingLogFile(rotateConf))
 }
 
-func (r *FSRepo) closeDatastore() error {
-	dsLock.Lock()
-	defer dsLock.Unlock()
-
-	dsPath := path.Join(r.path, defaultDataStoreDirectory)
-
-	// decrement the Opener count. if this goroutine is the last, also close
-	// the underlying datastore (and remove its reference from the map)
-
-	dsOpenersCounter.RemoveOpener(dsPath)
-
-	if dsOpenersCounter.NumOpeners(dsPath) == 0 {
-		delete(datastores, dsPath) // remove the reference
-		return r.ds.Close()
-	}
-	return nil
-}
-
 // Close closes the FSRepo, releasing held resources.
 func (r *FSRepo) Close() error {
 	packageLock.Lock()
@@ -322,7 +278,7 @@ func (r *FSRepo) Close() error {
 		return debugerror.Errorf("repo is %s", r.state)
 	}
 
-	if err := r.closeDatastore(); err != nil {
+	if err := r.ds.Close(); err != nil {
 		return err
 	}