--- /dev/null
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package gatefs provides an implementation of the FileSystem
+// interface that wraps another FileSystem and limits its concurrency.
+package gatefs // import "golang.org/x/tools/godoc/vfs/gatefs"
+
+import (
+ "fmt"
+ "os"
+
+ "golang.org/x/tools/godoc/vfs"
+)
+
+// New returns a new FileSystem that delegates to fs.
+// If gateCh is non-nil and buffered, it's used as a gate
+// to limit concurrency on calls to fs.
+func New(fs vfs.FileSystem, gateCh chan bool) vfs.FileSystem {
+ if cap(gateCh) == 0 {
+ return fs
+ }
+ return gatefs{fs, gate(gateCh)}
+}
+
+type gate chan bool
+
+func (g gate) enter() { g <- true }
+func (g gate) leave() { <-g }
+
+type gatefs struct {
+ fs vfs.FileSystem
+ gate
+}
+
+func (fs gatefs) String() string {
+ return fmt.Sprintf("gated(%s, %d)", fs.fs.String(), cap(fs.gate))
+}
+
+func (fs gatefs) RootType(path string) vfs.RootType {
+ return fs.fs.RootType(path)
+}
+
+func (fs gatefs) Open(p string) (vfs.ReadSeekCloser, error) {
+ fs.enter()
+ defer fs.leave()
+ rsc, err := fs.fs.Open(p)
+ if err != nil {
+ return nil, err
+ }
+ return gatef{rsc, fs.gate}, nil
+}
+
+func (fs gatefs) Lstat(p string) (os.FileInfo, error) {
+ fs.enter()
+ defer fs.leave()
+ return fs.fs.Lstat(p)
+}
+
+func (fs gatefs) Stat(p string) (os.FileInfo, error) {
+ fs.enter()
+ defer fs.leave()
+ return fs.fs.Stat(p)
+}
+
+func (fs gatefs) ReadDir(p string) ([]os.FileInfo, error) {
+ fs.enter()
+ defer fs.leave()
+ return fs.fs.ReadDir(p)
+}
+
+type gatef struct {
+ rsc vfs.ReadSeekCloser
+ gate
+}
+
+func (f gatef) Read(p []byte) (n int, err error) {
+ f.enter()
+ defer f.leave()
+ return f.rsc.Read(p)
+}
+
+func (f gatef) Seek(offset int64, whence int) (ret int64, err error) {
+ f.enter()
+ defer f.leave()
+ return f.rsc.Seek(offset, whence)
+}
+
+func (f gatef) Close() error {
+ f.enter()
+ defer f.leave()
+ return f.rsc.Close()
+}