luci-go/common/dirwalk: Code for walking a directory tree efficiently

common/dirwalk/walkparallel.go

Index: common/dirwalk/walkparallel.go
diff --git a/common/dirwalk/walkparallel.go b/common/dirwalk/walkparallel.go
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+++ b/common/dirwalk/walkparallel.go
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+// Copyright 2016 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+// On the majority of systems testing shows that this function is either
+// slower than (or at best comparable) the non-parallel version while consuming
+// many times the resources.
+//
+// Linux Kernel versions newer than >4.8 which disable locks in stat path can
+// make this version faster.
+//
+// Use the performance tests to determine the correct walker for your platform
+// and system!
+
+package dirwalk
+
+import (
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"sort"
+	"sync/atomic"
+
+	"github.com/eapache/channels"
+)
+
+type fileQueue struct {
+	queued   uint64
+	finished uint64
+	items    channels.Channel
+	waiton   chan bool
+}
+
+func (q *fileQueue) add(s string) {
+	atomic.AddUint64(&q.queued, 1)
+	q.items.In() <- s
+}
+
+func (q *fileQueue) done() {
+	atomic.AddUint64(&q.finished, 1)
+
+	if q.queued == q.finished {
+		q.items.Close()
+		q.waiton <- true
+	}
+}
+
+func (q *fileQueue) wait() {
+	<-q.waiton
+}
+
+func examinePath(queue *fileQueue, smallfile_limit int64, obs WalkObserver) {
+	for ipath := range queue.items.Out() {
+		path := ipath.(string)
+
+		fi, err := os.Stat(path)
+		if err != nil {
+			obs.Error(path, err)
+			return
+		}
+
+		if fi.IsDir() {
+			f, err := os.Open(path)
+			if err != nil {
+				obs.Error(path, err)
+			}
+
+			dircontents, err := f.Readdirnames(-1)
+			if err != nil {
+				obs.Error(path, err)
+			}
+			sort.Strings(dircontents)
+			for _, name := range dircontents {
+				fname := filepath.Join(path, name)
+				queue.add(fname)
+			}
+		} else {
+			if fi.Size() < smallfile_limit {
+				data, err := ioutil.ReadFile(path)
+				if err != nil {
+					obs.Error(path, err)
+					return
+				}
+				if int64(len(data)) != fi.Size() {
+					panic("file size was wrong!")
+				}
+				obs.SmallFile(path, data)
+			} else {
+				obs.LargeFile(path)
+			}
+		}
+		queue.done()
+	}
+}
+
+func WalkParallel(root string, smallfile_limit int64, obs WalkObserver) {
+	queue := fileQueue{queued: 0, finished: 0, items: channels.NewInfiniteChannel(), waiton: make(chan bool)}
+
+	for w := 0; w <= 10; w++ {
+		go examinePath(&queue, smallfile_limit, obs)
+	}
+
+	queue.add(root)
+	queue.wait()
+	obs.Finished()
+}