Matthias Andreas Benkard | 832a54e | 2019-01-29 09:27:38 +0100 | [diff] [blame] | 1 | // Copyright 2016 The Go Authors. All rights reserved. |
| 2 | // Use of this source code is governed by a BSD-style |
| 3 | // license that can be found in the LICENSE file. |
| 4 | |
| 5 | // Package fastwalk provides a faster version of filepath.Walk for file system |
| 6 | // scanning tools. |
| 7 | package fastwalk |
| 8 | |
| 9 | import ( |
| 10 | "errors" |
| 11 | "os" |
| 12 | "path/filepath" |
| 13 | "runtime" |
| 14 | "sync" |
| 15 | ) |
| 16 | |
| 17 | // TraverseLink is used as a return value from WalkFuncs to indicate that the |
| 18 | // symlink named in the call may be traversed. |
| 19 | var TraverseLink = errors.New("fastwalk: traverse symlink, assuming target is a directory") |
| 20 | |
| 21 | // Walk is a faster implementation of filepath.Walk. |
| 22 | // |
| 23 | // filepath.Walk's design necessarily calls os.Lstat on each file, |
| 24 | // even if the caller needs less info. |
| 25 | // Many tools need only the type of each file. |
| 26 | // On some platforms, this information is provided directly by the readdir |
| 27 | // system call, avoiding the need to stat each file individually. |
| 28 | // fastwalk_unix.go contains a fork of the syscall routines. |
| 29 | // |
| 30 | // See golang.org/issue/16399 |
| 31 | // |
| 32 | // Walk walks the file tree rooted at root, calling walkFn for |
| 33 | // each file or directory in the tree, including root. |
| 34 | // |
| 35 | // If fastWalk returns filepath.SkipDir, the directory is skipped. |
| 36 | // |
| 37 | // Unlike filepath.Walk: |
| 38 | // * file stat calls must be done by the user. |
| 39 | // The only provided metadata is the file type, which does not include |
| 40 | // any permission bits. |
| 41 | // * multiple goroutines stat the filesystem concurrently. The provided |
| 42 | // walkFn must be safe for concurrent use. |
| 43 | // * fastWalk can follow symlinks if walkFn returns the TraverseLink |
| 44 | // sentinel error. It is the walkFn's responsibility to prevent |
| 45 | // fastWalk from going into symlink cycles. |
| 46 | func Walk(root string, walkFn func(path string, typ os.FileMode) error) error { |
| 47 | // TODO(bradfitz): make numWorkers configurable? We used a |
| 48 | // minimum of 4 to give the kernel more info about multiple |
| 49 | // things we want, in hopes its I/O scheduling can take |
| 50 | // advantage of that. Hopefully most are in cache. Maybe 4 is |
| 51 | // even too low of a minimum. Profile more. |
| 52 | numWorkers := 4 |
| 53 | if n := runtime.NumCPU(); n > numWorkers { |
| 54 | numWorkers = n |
| 55 | } |
| 56 | |
| 57 | // Make sure to wait for all workers to finish, otherwise |
| 58 | // walkFn could still be called after returning. This Wait call |
| 59 | // runs after close(e.donec) below. |
| 60 | var wg sync.WaitGroup |
| 61 | defer wg.Wait() |
| 62 | |
| 63 | w := &walker{ |
| 64 | fn: walkFn, |
| 65 | enqueuec: make(chan walkItem, numWorkers), // buffered for performance |
| 66 | workc: make(chan walkItem, numWorkers), // buffered for performance |
| 67 | donec: make(chan struct{}), |
| 68 | |
| 69 | // buffered for correctness & not leaking goroutines: |
| 70 | resc: make(chan error, numWorkers), |
| 71 | } |
| 72 | defer close(w.donec) |
| 73 | |
| 74 | for i := 0; i < numWorkers; i++ { |
| 75 | wg.Add(1) |
| 76 | go w.doWork(&wg) |
| 77 | } |
| 78 | todo := []walkItem{{dir: root}} |
| 79 | out := 0 |
| 80 | for { |
| 81 | workc := w.workc |
| 82 | var workItem walkItem |
| 83 | if len(todo) == 0 { |
| 84 | workc = nil |
| 85 | } else { |
| 86 | workItem = todo[len(todo)-1] |
| 87 | } |
| 88 | select { |
| 89 | case workc <- workItem: |
| 90 | todo = todo[:len(todo)-1] |
| 91 | out++ |
| 92 | case it := <-w.enqueuec: |
| 93 | todo = append(todo, it) |
| 94 | case err := <-w.resc: |
| 95 | out-- |
| 96 | if err != nil { |
| 97 | return err |
| 98 | } |
| 99 | if out == 0 && len(todo) == 0 { |
| 100 | // It's safe to quit here, as long as the buffered |
| 101 | // enqueue channel isn't also readable, which might |
| 102 | // happen if the worker sends both another unit of |
| 103 | // work and its result before the other select was |
| 104 | // scheduled and both w.resc and w.enqueuec were |
| 105 | // readable. |
| 106 | select { |
| 107 | case it := <-w.enqueuec: |
| 108 | todo = append(todo, it) |
| 109 | default: |
| 110 | return nil |
| 111 | } |
| 112 | } |
| 113 | } |
| 114 | } |
| 115 | } |
| 116 | |
| 117 | // doWork reads directories as instructed (via workc) and runs the |
| 118 | // user's callback function. |
| 119 | func (w *walker) doWork(wg *sync.WaitGroup) { |
| 120 | defer wg.Done() |
| 121 | for { |
| 122 | select { |
| 123 | case <-w.donec: |
| 124 | return |
| 125 | case it := <-w.workc: |
| 126 | select { |
| 127 | case <-w.donec: |
| 128 | return |
| 129 | case w.resc <- w.walk(it.dir, !it.callbackDone): |
| 130 | } |
| 131 | } |
| 132 | } |
| 133 | } |
| 134 | |
| 135 | type walker struct { |
| 136 | fn func(path string, typ os.FileMode) error |
| 137 | |
| 138 | donec chan struct{} // closed on fastWalk's return |
| 139 | workc chan walkItem // to workers |
| 140 | enqueuec chan walkItem // from workers |
| 141 | resc chan error // from workers |
| 142 | } |
| 143 | |
| 144 | type walkItem struct { |
| 145 | dir string |
| 146 | callbackDone bool // callback already called; don't do it again |
| 147 | } |
| 148 | |
| 149 | func (w *walker) enqueue(it walkItem) { |
| 150 | select { |
| 151 | case w.enqueuec <- it: |
| 152 | case <-w.donec: |
| 153 | } |
| 154 | } |
| 155 | |
| 156 | func (w *walker) onDirEnt(dirName, baseName string, typ os.FileMode) error { |
| 157 | joined := dirName + string(os.PathSeparator) + baseName |
| 158 | if typ == os.ModeDir { |
| 159 | w.enqueue(walkItem{dir: joined}) |
| 160 | return nil |
| 161 | } |
| 162 | |
| 163 | err := w.fn(joined, typ) |
| 164 | if typ == os.ModeSymlink { |
| 165 | if err == TraverseLink { |
| 166 | // Set callbackDone so we don't call it twice for both the |
| 167 | // symlink-as-symlink and the symlink-as-directory later: |
| 168 | w.enqueue(walkItem{dir: joined, callbackDone: true}) |
| 169 | return nil |
| 170 | } |
| 171 | if err == filepath.SkipDir { |
| 172 | // Permit SkipDir on symlinks too. |
| 173 | return nil |
| 174 | } |
| 175 | } |
| 176 | return err |
| 177 | } |
| 178 | |
| 179 | func (w *walker) walk(root string, runUserCallback bool) error { |
| 180 | if runUserCallback { |
| 181 | err := w.fn(root, os.ModeDir) |
| 182 | if err == filepath.SkipDir { |
| 183 | return nil |
| 184 | } |
| 185 | if err != nil { |
| 186 | return err |
| 187 | } |
| 188 | } |
| 189 | |
| 190 | return readDir(root, w.onDirEnt) |
| 191 | } |