memfs: Remove memfs.WithoutMutex

Ensure memfs is thread-safe at all times. In case the single thread
performance is more important (probably outside of go-git) that can
be fixed with future optimisation.

In the context of go-git, this should not be a concern as there are
other bottlenecks (e.g. sha1cd).

Signed-off-by: Paulo Gomes <[email protected]>

Author: pjbgf

memfs/memory.go

@@ -10,6 +10,7 @@ import (
 	"path/filepath"
 	"sort"
 	"strings"
+	"sync"
 	"syscall"
 
 	"github.com/go-git/go-billy/v6"
@@ -23,23 +24,19 @@ const separator = filepath.Separator
 type Memory struct {
 	s *storage
 
-	m mutex
+	m sync.RWMutex
 }
 
 // New returns a new Memory filesystem.
 func New(opts ...Option) billy.Filesystem {
-	o := &options{
-		// Enable thread-safety by default.
-		newMutex: newMutex,
-	}
-
+	o := &options{}
 	for _, opt := range opts {
 		opt(o)
 	}
 
 	fs := &Memory{
-		s: newStorage(o.newMutex),
-		m: o.newMutex(),
+		s: newStorage(),
+		m: sync.RWMutex{},
 	}
 	_, err := fs.s.New("/", 0755|os.ModeDir, 0)
 	if err != nil {

memfs/memory_option.go

@@ -3,13 +3,4 @@ package memfs
 type Option func(*options)
 
 type options struct {
-	newMutex func() mutex
-}
-
-// WithoutMutex disables thread safety. This is a temporary option
-// for users to opt-out from the default setting.
-func WithoutMutex() Option {
-	return func(o *options) {
-		o.newMutex = newNoOpMutex
-	}
 }

memfs/mutex.go

@@ -6,6 +6,7 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+	"sync"
 	"time"
 
 	"github.com/go-git/go-billy/v6"
@@ -15,16 +16,14 @@ type storage struct {
 	files    map[string]*file
 	children map[string]map[string]*file
 
-	mf mutex
-	mc mutex
+	mf sync.RWMutex
+	mc sync.RWMutex
 }
 
-func newStorage(newMutex func() mutex) *storage {
+func newStorage() *storage {
 	return &storage{
 		files:    make(map[string]*file, 0),
 		children: make(map[string]map[string]*file, 0),
-		mc:       newMutex(),
-		mf:       newMutex(),
 	}
 }
 

memfs/storage.go

@@ -55,13 +55,6 @@ func BenchmarkCompare(b *testing.B) {
 		{
 			name:    "memfs",
 			fn:      fn,
-			sut:     memfs.New(memfs.WithoutMutex()),
-			openF:   billyOpen,
-			createF: billyCreate,
-		},
-		{
-			name:    "memfs_mutex",
-			fn:      fn,
 			sut:     memfs.New(),
 			openF:   billyOpen,
 			createF: billyCreate,