From fec995ab483a4fc6b2859d199d211c25b6661ff7 Mon Sep 17 00:00:00 2001
From: Laria Carolin Chabowski <laria@laria.me>
Date: Wed, 27 Sep 2017 08:30:51 +0200
Subject: WriteDir in parallel

---
 backup/backup.go | 129 +++++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 111 insertions(+), 18 deletions(-)

diff --git a/backup/backup.go b/backup/backup.go
index f578e6f..84fb554 100644
--- a/backup/backup.go
+++ b/backup/backup.go
@@ -6,23 +6,105 @@ import (
 	"code.laria.me/petrific/objects"
 	"code.laria.me/petrific/storage"
 	"io"
+	"runtime"
+	"sort"
 	"time"
 )
 
+type filesLast []fs.File
+
+func (fl filesLast) Len() int           { return len(fl) }
+func (fl filesLast) Less(i, j int) bool { return fl[i].Type() != fs.FFile && fl[j].Type() == fs.FFile }
+func (fl filesLast) Swap(i, j int)      { fl[i], fl[j] = fl[j], fl[i] }
+
+type writeFileTaskResult struct {
+	file    fs.RegularFile
+	file_id objects.ObjectId
+	err     error
+}
+
+type writeFileTask struct {
+	file   fs.RegularFile
+	result *chan writeFileTaskResult
+}
+
+func (task writeFileTask) process(store storage.Storage) {
+	var result writeFileTaskResult
+	result.file = task.file
+
+	rwc, err := task.file.Open()
+	if err != nil {
+		result.err = err
+		*(task.result) <- result
+		return
+	}
+	defer rwc.Close()
+
+	result.file_id, result.err = WriteFile(store, rwc)
+
+	*(task.result) <- result
+}
+
+type writeDirProcess struct {
+	queue chan writeFileTask
+	store storage.Storage
+}
+
+func (proc writeDirProcess) worker() {
+	for task := range proc.queue {
+		task.process(proc.store)
+	}
+}
+
+func (proc writeDirProcess) enqueue(file fs.RegularFile, result *chan writeFileTaskResult) {
+	go func() {
+		proc.queue <- writeFileTask{file, result}
+	}()
+}
+
+func (proc writeDirProcess) stop() {
+	close(proc.queue)
+}
+
 func WriteDir(
 	store storage.Storage,
 	abspath string,
 	d fs.Dir,
 	pcache cache.Cache,
 ) (objects.ObjectId, error) {
-	children, err := d.Readdir()
+	proc := writeDirProcess{
+		make(chan writeFileTask),
+		store,
+	}
+	defer proc.stop()
+
+	for i := 0; i < runtime.NumCPU(); i++ {
+		go proc.worker()
+	}
+
+	return proc.writeDir(abspath, d, pcache)
+}
+
+func (proc writeDirProcess) writeDir(
+	abspath string,
+	d fs.Dir,
+	pcache cache.Cache,
+) (objects.ObjectId, error) {
+	_children, err := d.Readdir()
 	if err != nil {
 		return objects.ObjectId{}, err
 	}
 
+	file_results := make(chan writeFileTaskResult)
+	wait_for_files := 0
+
+	// fs.FFile entries must be processed at the end, since they are processed concurrently and might otherwise lock us up
+	children := filesLast(_children)
+	sort.Sort(children)
+
 	infos := make(objects.Tree)
 	for _, c := range children {
-		var info objects.TreeEntry
+		var info objects.TreeEntry = nil
 
 		switch c.Type() {
 		case fs.FFile:
@@ -30,23 +112,13 @@ func WriteDir(
 			if !ok || mtime.Before(c.ModTime()) {
 				// According to cache the file was changed
 
-				rwc, err := c.(fs.RegularFile).Open()
-				if err != nil {
-					return objects.ObjectId{}, err
-				}
-
-				file_id, err = WriteFile(store, rwc)
-				rwc.Close()
-				if err != nil {
-					return objects.ObjectId{}, err
-				}
-
-				pcache.SetPathUpdated(abspath+"/"+c.Name(), c.ModTime(), file_id)
+				proc.enqueue(c.(fs.RegularFile), &file_results)
+				wait_for_files++
+			} else {
+				info = objects.NewTreeEntryFile(file_id, c.Executable())
 			}
-
-			info = objects.NewTreeEntryFile(file_id, c.Executable())
 		case fs.FDir:
-			subtree_id, err := WriteDir(store, abspath+"/"+c.Name(), c.(fs.Dir), pcache)
+			subtree_id, err := proc.writeDir(abspath+"/"+c.Name(), c.(fs.Dir), pcache)
 			if err != nil {
 				return objects.ObjectId{}, err
 			}
@@ -66,7 +138,28 @@ func WriteDir(
 		}
 	}
 
-	return storage.SetObject(store, objects.ToRawObject(infos))
+	for ; wait_for_files > 0; wait_for_files-- {
+		result := <-file_results
+		if result.err != nil {
+			err = result.err
+			wait_for_files--
+			break
+		}
+
+		pcache.SetPathUpdated(abspath+"/"+result.file.Name(), result.file.ModTime(), result.file_id)
+		infos[result.file.Name()] = objects.NewTreeEntryFile(result.file_id, result.file.Executable())
+	}
+
+	for ; wait_for_files > 0; wait_for_files-- {
+		// Drain remaining results in case of error
+		<-file_results
+	}
+
+	if err != nil {
+		return objects.ObjectId{}, err
+	}
+
+	return storage.SetObject(proc.store, objects.ToRawObject(infos))
 }
 
 const BlobChunkSize = 16 * 1024 * 1024 // 16MB
-- 
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