Parallelize imports and thumbnailing

3 files changed, 121 insertions, 52 deletions

diff --git a/go.mod b/go.mod
index 6d8c4f9..42e6176 100644
--- a/go.mod
+++ b/go.mod
@@ -2,4 +2,7 @@ module janouch.name/gallery
 
 go 1.21.4
 
-require github.com/mattn/go-sqlite3 v1.14.18
+require (
+	github.com/mattn/go-sqlite3 v1.14.18
+	golang.org/x/sync v0.5.0
+)
diff --git a/go.sum b/go.sum
index 810a101..a5de6f1 100644
--- a/go.sum
+++ b/go.sum
@@ -1,2 +1,4 @@
 github.com/mattn/go-sqlite3 v1.14.18 h1:JL0eqdCOq6DJVNPSvArO/bIV9/P7fbGrV00LZHc+5aI=
 github.com/mattn/go-sqlite3 v1.14.18/go.mod h1:2eHXhiwb8IkHr+BDWZGa96P6+rkvnG63S2DGjv9HUNg=
+golang.org/x/sync v0.5.0 h1:60k92dhOjHxJkrqnwsfl8KuaHbn/5dl0lUPUklKo3qE=
+golang.org/x/sync v0.5.0/go.mod h1:Czt+wKu1gCyEFDUtn0jG5QVvpJ6rzVqr5aXyt9drQfk=
diff --git a/main.go b/main.go
index e6eae07..a57f3af 100644
--- a/main.go
+++ b/main.go
@@ -2,6 +2,7 @@ package main
 
 import (
 	"bytes"
+	"context"
 	"crypto/sha1"
 	"database/sql"
 	"encoding/hex"
@@ -17,32 +18,38 @@ import (
 	"os/exec"
 	"path/filepath"
 	"regexp"
+	"runtime"
 	"strconv"
 	"strings"
+	"sync"
 	"time"
 
 	_ "github.com/mattn/go-sqlite3"
+	"golang.org/x/sync/semaphore"
 )
 
 var (
-	db *sql.DB // sqlite database
-	gd string  // gallery directory
+	db               *sql.DB // sqlite database
+	galleryDirectory string  // gallery directory
+
+	// taskSemaphore limits parallel computations.
+	taskSemaphore *semaphore.Weighted
 )
 
 func openDB(directory string) error {
 	var err error
 	db, err = sql.Open("sqlite3",
 		"file:"+filepath.Join(directory, "gallery.db?_foreign_keys=1"))
-	gd = directory
+	galleryDirectory = directory
 	return err
 }
 
 func imagePath(sha1 string) string {
-	return filepath.Join(gd, "images", sha1[:2], sha1)
+	return filepath.Join(galleryDirectory, "images", sha1[:2], sha1)
 }
 
 func thumbPath(sha1 string) string {
-	return filepath.Join(gd, "thumbs", sha1[:2], sha1+".webp")
+	return filepath.Join(galleryDirectory, "thumbs", sha1[:2], sha1+".webp")
 }
 
 func dbCollectStrings(query string) ([]string, error) {
@@ -70,27 +77,10 @@ type directoryManager struct {
 	cache map[string]int64 // Unix-style paths to directory.id
 }
 
-func (dm *directoryManager) IDForDirectoryPath(
-	tx *sql.Tx, path string) (int64, error) {
-	// Relative paths could be handled differently,
-	// but right now, they're assumed to start at the root.
-	path = filepath.ToSlash(filepath.Clean(path))
-	list := strings.Split(path, "/")
-	if len(list) > 1 && list[0] == "" {
-		list = list[1:]
-	}
-	if len(list) == 0 {
-		return 0, nil
-	}
-
-	if dm.cache == nil {
-		dm.cache = make(map[string]int64)
-	} else if id, ok := dm.cache[path]; ok {
-		return id, nil
-	}
-
+func (dm *directoryManager) uncachedIDForPath(
+	tx *sql.Tx, path []string) (int64, error) {
 	var parent sql.NullInt64
-	for _, name := range list {
+	for _, name := range path {
 		if err := tx.QueryRow(
 			`SELECT id FROM directory WHERE name = ? AND parent IS ?`,
 			name, parent).Scan(&parent); err == nil {
@@ -109,10 +99,36 @@ func (dm *directoryManager) IDForDirectoryPath(
 			parent = sql.NullInt64{Int64: id, Valid: true}
 		}
 	}
-	dm.cache[path] = parent.Int64
 	return parent.Int64, nil
 }
 
+func (dm *directoryManager) IDForDirectoryPath(
+	tx *sql.Tx, path string) (int64, error) {
+	// Relative paths could be handled differently,
+	// but right now, they're assumed to start at the root.
+	path = filepath.ToSlash(filepath.Clean(path))
+	list := strings.Split(path, "/")
+	if len(list) > 1 && list[0] == "" {
+		list = list[1:]
+	}
+	if len(list) == 0 {
+		return 0, nil
+	}
+
+	if dm.cache == nil {
+		dm.cache = make(map[string]int64)
+	} else if id, ok := dm.cache[path]; ok {
+		return id, nil
+	}
+
+	id, err := dm.uncachedIDForPath(tx, list)
+	if err != nil {
+		return 0, err
+	}
+	dm.cache[path] = id
+	return id, nil
+}
+
 // XXX: This is preliminary.
 type entry struct {
 	Parent int64
@@ -197,10 +213,12 @@ func cmdInit(args []string) error {
 
 	// XXX: There's technically no reason to keep images as symlinks,
 	// we might just keep absolute paths in the database as well.
-	if err := os.MkdirAll(filepath.Join(gd, "images"), 0755); err != nil {
+	if err := os.MkdirAll(
+		filepath.Join(galleryDirectory, "images"), 0755); err != nil {
 		return err
 	}
-	if err := os.MkdirAll(filepath.Join(gd, "thumbs"), 0755); err != nil {
+	if err := os.MkdirAll(
+		filepath.Join(galleryDirectory, "thumbs"), 0755); err != nil {
 		return err
 	}
 	return nil
@@ -323,7 +341,8 @@ func isImage(path string) (bool, error) {
 }
 
 type importer struct {
-	dm directoryManager
+	dm      directoryManager
+	dmMutex sync.Mutex
 }
 
 func (i *importer) Import(path string, d fs.DirEntry, err error) error {
@@ -376,6 +395,13 @@ func (i *importer) Import(path string, d fs.DirEntry, err error) error {
 		return err
 	}
 
+	// A concurrent transaction could be aborted, yet still result in
+	// creating directoryManager's cache entry, therefore this scope.
+	// TODO: Educate self about isolation levels and reconsider.
+	// Perhaps get rid of the cache.
+	i.dmMutex.Lock()
+	defer i.dmMutex.Unlock()
+
 	tx, err := db.Begin()
 	if err != nil {
 		return err
@@ -393,9 +419,8 @@ func (i *importer) Import(path string, d fs.DirEntry, err error) error {
 		return err
 	}
 
-	_, err = tx.Exec(`INSERT INTO entry(
-		parent, name, mtime, sha1
-	) VALUES (?, ?, ?, ?)`, dbParent, dbBasename, s.ModTime().Unix(), hexSHA1)
+	_, err = tx.Exec(`INSERT INTO entry(parent, name, mtime, sha1)
+		VALUES (?, ?, ?, ?)`, dbParent, dbBasename, s.ModTime().Unix(), hexSHA1)
 	if err != nil {
 		return err
 	}
@@ -412,17 +437,34 @@ func cmdImport(args []string) error {
 		return err
 	}
 
-	// TODO: This would better be done in parallel (making hashes).
 	// TODO: Show progress in some manner. Perhaps port my propeller code.
+	ctx, cancel := context.WithCancelCause(context.Background())
 	i := importer{}
+	wg := sync.WaitGroup{}
 	for _, name := range args[1:] {
-		if err := filepath.WalkDir(name,
-			func(path string, d fs.DirEntry, err error) error {
-				return i.Import(path, d, err)
-			}); err != nil {
+		cb := func(path string, d fs.DirEntry, err error) error {
+			if taskSemaphore.Acquire(ctx, 1) != nil {
+				return context.Cause(ctx)
+			}
+
+			wg.Add(1)
+			go func() {
+				defer taskSemaphore.Release(1)
+				defer wg.Done()
+				if err := i.Import(path, d, err); err != nil {
+					cancel(err)
+				}
+			}()
+			return nil
+		}
+		if err := filepath.WalkDir(name, cb); err != nil {
 			return err
 		}
 	}
+	wg.Wait()
+	if ctx.Err() != nil {
+		return context.Cause(ctx)
+	}
 	return nil
 }
 
@@ -472,10 +514,12 @@ func makeThumbnail(pathImage, pathThumb string) (int, int, error) {
 	//
 	// TODO: See if we can optimize resulting WebP animations.
 	// (Do -layers optimize* apply to this format at all?)
-	cmd := exec.Command("convert", pathImage, "-coalesce", "-colorspace", "RGB",
-		"-auto-orient", "-strip", "-resize", "256x128>", "-colorspace", "sRGB",
+	cmd := exec.Command("convert", "-limit", "thread", "1", pathImage,
+		"-coalesce", "-colorspace", "RGB", "-auto-orient", "-strip",
+		"-resize", "256x128>", "-colorspace", "sRGB",
 		"-format", "%w %h", "+write", pathThumb, "-delete", "1--1", "info:")
 
+	// XXX: Early returns may leak resources.
 	stdout, err := cmd.StdoutPipe()
 	if err != nil {
 		return 0, 0, err
@@ -496,6 +540,19 @@ func makeThumbnail(pathImage, pathThumb string) (int, int, error) {
 	return w, h, err
 }
 
+func makeThumbnailFor(sha1 string) error {
+	pathImage := imagePath(sha1)
+	pathThumb := thumbPath(sha1)
+	w, h, err := makeThumbnail(pathImage, pathThumb)
+	if err != nil {
+		return err
+	}
+
+	_, err = db.Exec(`UPDATE image SET thumbw = ?, thumbh = ?
+		WHERE sha1 = ?`, w, h, sha1)
+	return err
+}
+
 // cmdThumbnail generates missing thumbnails, in parallel.
 func cmdThumbnail(args []string) error {
 	if len(args) < 1 {
@@ -516,28 +573,34 @@ func cmdThumbnail(args []string) error {
 		}
 	}
 
-	// TODO: Try to run the thumbnailer in parallel, somehow.
-	// Then run convert with `-limit thread 1`.
 	// TODO: Show progress in some manner. Perhaps port my propeller code.
+	ctx, cancel := context.WithCancelCause(context.Background())
+	wg := sync.WaitGroup{}
 	for _, sha1 := range hexSHA1 {
-		pathImage := imagePath(sha1)
-		pathThumb := thumbPath(sha1)
-		w, h, err := makeThumbnail(pathImage, pathThumb)
-		if err != nil {
-			return err
+		if taskSemaphore.Acquire(ctx, 1) != nil {
+			break
 		}
 
-		_, err = db.Exec(`UPDATE image SET thumbw = ?, thumbh = ?
-			WHERE sha1 = ?`, w, h, sha1)
-		if err != nil {
-			return err
-		}
+		wg.Add(1)
+		go func(sha1 string) {
+			defer taskSemaphore.Release(1)
+			defer wg.Done()
+			if err := makeThumbnailFor(sha1); err != nil {
+				cancel(err)
+			}
+		}(sha1)
+	}
+	wg.Wait()
+	if ctx.Err() != nil {
+		return context.Cause(ctx)
 	}
 	return nil
 }
 
 func makeDhash(hasher, pathThumb string) (uint64, error) {
 	cmd := exec.Command(hasher, pathThumb)
+
+	// XXX: Early returns may leak resources.
 	stdout, err := cmd.StdoutPipe()
 	if err != nil {
 		return 0, err
@@ -617,6 +680,7 @@ func main() {
 		log.Fatalln("Unknown command: " + os.Args[1])
 	}
 
+	taskSemaphore = semaphore.NewWeighted(int64(runtime.NumCPU()))
 	err := cmd.handler(os.Args[2:])
 
 	// Note that the database object has a closing finalizer,