From 23aeca85fff13aacce341d67d2cafc4f0a195214 Mon Sep 17 00:00:00 2001
From: Alexander Neumann <alexander@bumpern.de>
Date: Tue, 27 Oct 2015 22:44:10 +0100
Subject: [PATCH] load trees in parallel

---
 walk.go | 162 +++++++++++++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 143 insertions(+), 19 deletions(-)

diff --git a/walk.go b/walk.go
index 1e5979328..5cceb98b0 100644
--- a/walk.go
+++ b/walk.go
@@ -2,11 +2,14 @@ package restic
 
 import (
 	"path/filepath"
+	"sync"
 
 	"github.com/restic/restic/backend"
 	"github.com/restic/restic/debug"
+	"github.com/restic/restic/pack"
 )
 
+// WalkTreeJob is a job sent from the tree walker.
 type WalkTreeJob struct {
 	Path  string
 	Error error
@@ -15,47 +18,168 @@ type WalkTreeJob struct {
 	Tree *Tree
 }
 
-func walkTree(repo TreeLoader, path string, treeID backend.ID, done chan struct{}, jobCh chan<- WalkTreeJob) {
-	debug.Log("walkTree", "start on %q (%v)", path, treeID.Str())
+// TreeWalker traverses a tree in the repository depth-first and sends a job
+// for each item (file or dir) that it encounters.
+type TreeWalker struct {
+	ch  chan<- loadTreeJob
+	out chan<- WalkTreeJob
+}
 
-	t, err := LoadTree(repo, treeID)
-	if err != nil {
+// NewTreeWalker uses ch to load trees from the repository and sends jobs to
+// out.
+func NewTreeWalker(ch chan<- loadTreeJob, out chan<- WalkTreeJob) *TreeWalker {
+	return &TreeWalker{ch: ch, out: out}
+}
+
+// Walk starts walking the tree given by id. When the channel done is closed,
+// processing stops.
+func (tw *TreeWalker) Walk(path string, id backend.ID, done chan struct{}) {
+	debug.Log("TreeWalker.Walk", "starting on tree %v for %v", id.Str(), path)
+	defer debug.Log("TreeWalker.Walk", "done walking tree %v for %v", id.Str(), path)
+
+	resCh := make(chan loadTreeResult, 1)
+	tw.ch <- loadTreeJob{
+		id:  id,
+		res: resCh,
+	}
+
+	res := <-resCh
+	if res.err != nil {
 		select {
-		case jobCh <- WalkTreeJob{Path: path, Error: err}:
+		case tw.out <- WalkTreeJob{Path: path, Error: res.err}:
 		case <-done:
 			return
 		}
 		return
 	}
 
-	for _, node := range t.Nodes {
-		p := filepath.Join(path, node.Name)
+	tw.walk(path, res.tree, done)
+
+	select {
+	case tw.out <- WalkTreeJob{Path: path, Tree: res.tree}:
+	case <-done:
+		return
+	}
+}
+
+func (tw *TreeWalker) walk(path string, tree *Tree, done chan struct{}) {
+	debug.Log("TreeWalker.walk", "start on %q", path)
+	defer debug.Log("TreeWalker.walk", "done for %q", path)
+
+	// load all subtrees in parallel
+	results := make([]<-chan loadTreeResult, len(tree.Nodes))
+	for i, node := range tree.Nodes {
 		if node.Type == "dir" {
-			walkTree(repo, p, *node.Subtree, done, jobCh)
+			resCh := make(chan loadTreeResult, 1)
+			tw.ch <- loadTreeJob{
+				id:  *node.Subtree,
+				res: resCh,
+			}
+
+			results[i] = resCh
+		}
+	}
+
+	for i, node := range tree.Nodes {
+		p := filepath.Join(path, node.Name)
+		var job WalkTreeJob
+
+		if node.Type == "dir" {
+			if results[i] == nil {
+				panic("result chan should not be nil")
+			}
+
+			res := <-results[i]
+			tw.walk(p, res.tree, done)
+
+			job = WalkTreeJob{Path: p, Tree: res.tree, Error: res.err}
 		} else {
+			job = WalkTreeJob{Path: p, Node: node}
+		}
+
+		select {
+		case tw.out <- job:
+		case <-done:
+			return
+		}
+	}
+}
+
+type loadTreeResult struct {
+	tree *Tree
+	err  error
+}
+
+type loadTreeJob struct {
+	id  backend.ID
+	res chan<- loadTreeResult
+}
+
+type treeLoader func(backend.ID) (*Tree, error)
+
+func loadTreeWorker(wg *sync.WaitGroup, in <-chan loadTreeJob, load treeLoader, done <-chan struct{}) {
+	debug.Log("loadTreeWorker", "start")
+	defer debug.Log("loadTreeWorker", "exit")
+	defer wg.Done()
+
+	for {
+		select {
+		case <-done:
+			debug.Log("loadTreeWorker", "done channel closed")
+			return
+		case job, ok := <-in:
+			if !ok {
+				debug.Log("loadTreeWorker", "input channel closed, exiting")
+				return
+			}
+
+			debug.Log("loadTreeWorker", "received job to load tree %v", job.id.Str())
+			tree, err := load(job.id)
+
+			debug.Log("loadTreeWorker", "tree %v loaded, error %v", job.id.Str(), err)
+
 			select {
-			case jobCh <- WalkTreeJob{Path: p, Node: node}:
+			case job.res <- loadTreeResult{tree, err}:
+				debug.Log("loadTreeWorker", "job result sent")
 			case <-done:
+				debug.Log("loadTreeWorker", "done channel closed before result could be sent")
 				return
 			}
 		}
 	}
-
-	select {
-	case jobCh <- WalkTreeJob{Path: path, Tree: t}:
-	case <-done:
-		return
-	}
-
-	debug.Log("walkTree", "done for %q (%v)", path, treeID.Str())
 }
 
+const loadTreeWorkers = 10
+
 // WalkTree walks the tree specified by id recursively and sends a job for each
 // file and directory it finds. When the channel done is closed, processing
 // stops.
 func WalkTree(repo TreeLoader, id backend.ID, done chan struct{}, jobCh chan<- WalkTreeJob) {
-	debug.Log("WalkTree", "start on %v", id.Str())
-	walkTree(repo, "", id, done, jobCh)
+	debug.Log("WalkTree", "start on %v, start workers", id.Str())
+
+	load := func(id backend.ID) (*Tree, error) {
+		tree := &Tree{}
+		err := repo.LoadJSONPack(pack.Tree, id, tree)
+		if err != nil {
+			return nil, err
+		}
+		return tree, nil
+	}
+
+	ch := make(chan loadTreeJob)
+
+	var wg sync.WaitGroup
+	for i := 0; i < loadTreeWorkers; i++ {
+		wg.Add(1)
+		go loadTreeWorker(&wg, ch, load, done)
+	}
+
+	tw := NewTreeWalker(ch, jobCh)
+	tw.Walk("", id, done)
 	close(jobCh)
+
+	close(ch)
+	wg.Wait()
+
 	debug.Log("WalkTree", "done")
 }