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Diffstat (limited to 'vendor/golang.org/x/tools/imports/fastwalk.go')
-rw-r--r-- | vendor/golang.org/x/tools/imports/fastwalk.go | 172 |
1 files changed, 172 insertions, 0 deletions
diff --git a/vendor/golang.org/x/tools/imports/fastwalk.go b/vendor/golang.org/x/tools/imports/fastwalk.go new file mode 100644 index 000000000..157c79225 --- /dev/null +++ b/vendor/golang.org/x/tools/imports/fastwalk.go @@ -0,0 +1,172 @@ +// Copyright 2016 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. + +// A faster implementation of filepath.Walk. +// +// filepath.Walk's design necessarily calls os.Lstat on each file, +// even if the caller needs less info. And goimports only need to know +// the type of each file. The kernel interface provides the type in +// the Readdir call but the standard library ignored it. +// fastwalk_unix.go contains a fork of the syscall routines. +// +// See golang.org/issue/16399 + +package imports + +import ( + "errors" + "os" + "path/filepath" + "runtime" +) + +// traverseLink is a sentinel error for fastWalk, similar to filepath.SkipDir. +var traverseLink = errors.New("traverse symlink, assuming target is a directory") + +// fastWalk walks the file tree rooted at root, calling walkFn for +// each file or directory in the tree, including root. +// +// If fastWalk returns filepath.SkipDir, the directory is skipped. +// +// Unlike filepath.Walk: +// * file stat calls must be done by the user. +// The only provided metadata is the file type, which does not include +// any permission bits. +// * multiple goroutines stat the filesystem concurrently. The provided +// walkFn must be safe for concurrent use. +// * fastWalk can follow symlinks if walkFn returns the traverseLink +// sentinel error. It is the walkFn's responsibility to prevent +// fastWalk from going into symlink cycles. +func fastWalk(root string, walkFn func(path string, typ os.FileMode) error) error { + // TODO(bradfitz): make numWorkers configurable? We used a + // minimum of 4 to give the kernel more info about multiple + // things we want, in hopes its I/O scheduling can take + // advantage of that. Hopefully most are in cache. Maybe 4 is + // even too low of a minimum. Profile more. + numWorkers := 4 + if n := runtime.NumCPU(); n > numWorkers { + numWorkers = n + } + w := &walker{ + fn: walkFn, + enqueuec: make(chan walkItem, numWorkers), // buffered for performance + workc: make(chan walkItem, numWorkers), // buffered for performance + donec: make(chan struct{}), + + // buffered for correctness & not leaking goroutines: + resc: make(chan error, numWorkers), + } + defer close(w.donec) + // TODO(bradfitz): start the workers as needed? maybe not worth it. + for i := 0; i < numWorkers; i++ { + go w.doWork() + } + todo := []walkItem{{dir: root}} + out := 0 + for { + workc := w.workc + var workItem walkItem + if len(todo) == 0 { + workc = nil + } else { + workItem = todo[len(todo)-1] + } + select { + case workc <- workItem: + todo = todo[:len(todo)-1] + out++ + case it := <-w.enqueuec: + todo = append(todo, it) + case err := <-w.resc: + out-- + if err != nil { + return err + } + if out == 0 && len(todo) == 0 { + // It's safe to quit here, as long as the buffered + // enqueue channel isn't also readable, which might + // happen if the worker sends both another unit of + // work and its result before the other select was + // scheduled and both w.resc and w.enqueuec were + // readable. + select { + case it := <-w.enqueuec: + todo = append(todo, it) + default: + return nil + } + } + } + } +} + +// doWork reads directories as instructed (via workc) and runs the +// user's callback function. +func (w *walker) doWork() { + for { + select { + case <-w.donec: + return + case it := <-w.workc: + w.resc <- w.walk(it.dir, !it.callbackDone) + } + } +} + +type walker struct { + fn func(path string, typ os.FileMode) error + + donec chan struct{} // closed on fastWalk's return + workc chan walkItem // to workers + enqueuec chan walkItem // from workers + resc chan error // from workers +} + +type walkItem struct { + dir string + callbackDone bool // callback already called; don't do it again +} + +func (w *walker) enqueue(it walkItem) { + select { + case w.enqueuec <- it: + case <-w.donec: + } +} + +func (w *walker) onDirEnt(dirName, baseName string, typ os.FileMode) error { + joined := dirName + string(os.PathSeparator) + baseName + if typ == os.ModeDir { + w.enqueue(walkItem{dir: joined}) + return nil + } + + err := w.fn(joined, typ) + if typ == os.ModeSymlink { + if err == traverseLink { + // Set callbackDone so we don't call it twice for both the + // symlink-as-symlink and the symlink-as-directory later: + w.enqueue(walkItem{dir: joined, callbackDone: true}) + return nil + } + if err == filepath.SkipDir { + // Permit SkipDir on symlinks too. + return nil + } + } + return err +} +func (w *walker) walk(root string, runUserCallback bool) error { + if runUserCallback { + err := w.fn(root, os.ModeDir) + if err == filepath.SkipDir { + return nil + } + if err != nil { + return err + } + } + + return readDir(root, w.onDirEnt) +} |