check: extract parallel index loading

internal/checker/checker.go

@@ -74,102 +74,38 @@ func (err ErrOldIndexFormat) Error() string {
 func (c *Checker) LoadIndex(ctx context.Context) (hints []error, errs []error) {
 	debug.Log("Start")
 
-	// track spawned goroutines using wg, create a new context which is
-	// cancelled as soon as an error occurs.
-	wg, wgCtx := errgroup.WithContext(ctx)
-
-	type FileInfo struct {
-		restic.ID
-		Size int64
-	}
-
-	type Result struct {
-		*repository.Index
-		restic.ID
-		Err error
-	}
-
-	ch := make(chan FileInfo)
-	resultCh := make(chan Result)
-
-	// send list of index files through ch, which is closed afterwards
-	wg.Go(func() error {
-		defer close(ch)
-		return c.repo.List(wgCtx, restic.IndexFile, func(id restic.ID, size int64) error {
-			select {
-			case <-wgCtx.Done():
-				return nil
-			case ch <- FileInfo{id, size}:
-			}
-			return nil
-		})
-	})
-
-	// a worker receives an index ID from ch, loads the index, and sends it to indexCh
-	worker := func() error {
-		var buf []byte
-		for fi := range ch {
-			debug.Log("worker got file %v", fi.ID.Str())
-			var err error
-			var idx *repository.Index
-			oldFormat := false
-
-			buf, err = c.repo.LoadAndDecrypt(wgCtx, buf[:0], restic.IndexFile, fi.ID)
-			if err == nil {
-				idx, oldFormat, err = repository.DecodeIndex(buf, fi.ID)
-			}
+	packToIndex := make(map[restic.ID]restic.IDSet)
+	err := repository.ForAllIndexes(ctx, c.repo, func(id restic.ID, index *repository.Index, oldFormat bool, err error) error {
+		debug.Log("process index %v, err %v", id, err)
 
 		if oldFormat {
-				debug.Log("index %v has old format", fi.ID.Str())
-				hints = append(hints, ErrOldIndexFormat{fi.ID})
+			debug.Log("index %v has old format", id.Str())
+			hints = append(hints, ErrOldIndexFormat{id})
 		}
 
-			err = errors.Wrapf(err, "error loading index %v", fi.ID.Str())
+		err = errors.Wrapf(err, "error loading index %v", id.Str())
 
-			select {
-			case resultCh <- Result{idx, fi.ID, err}:
-			case <-wgCtx.Done():
-			}
-		}
+		if err != nil {
+			errs = append(errs, err)
 			return nil
 		}
 
-	// run workers on ch
-	wg.Go(func() error {
-		defer close(resultCh)
-		return repository.RunWorkers(defaultParallelism, worker)
-	})
-
-	// receive decoded indexes
-	packToIndex := make(map[restic.ID]restic.IDSet)
-	wg.Go(func() error {
-		for res := range resultCh {
-			debug.Log("process index %v, err %v", res.ID, res.Err)
-
-			if res.Err != nil {
-				errs = append(errs, res.Err)
-				continue
-			}
-
-			c.masterIndex.Insert(res.Index)
+		c.masterIndex.Insert(index)
 
 		debug.Log("process blobs")
 		cnt := 0
-			for blob := range res.Index.Each(wgCtx) {
+		for blob := range index.Each(ctx) {
 			cnt++
 
 			if _, ok := packToIndex[blob.PackID]; !ok {
 				packToIndex[blob.PackID] = restic.NewIDSet()
 			}
-				packToIndex[blob.PackID].Insert(res.ID)
+			packToIndex[blob.PackID].Insert(id)
 		}
 
 		debug.Log("%d blobs processed", cnt)
-		}
 		return nil
 	})
-
-	err := wg.Wait()
 	if err != nil {
 		errs = append(errs, err)
 	}

internal/repository/index_parallel.go

@@ -0,0 +1,77 @@
+package repository
+
+import (
+	"context"
+	"sync"
+
+	"github.com/restic/restic/internal/debug"
+	"github.com/restic/restic/internal/restic"
+	"golang.org/x/sync/errgroup"
+)
+
+const loadIndexParallelism = 5
+
+// ForAllIndexes loads all index files in parallel and calls the given callback.
+// It is guaranteed that the function is not run concurrently. If the callback
+// returns an error, this function is cancelled and also returns that error.
+func ForAllIndexes(ctx context.Context, repo restic.Repository,
+	fn func(id restic.ID, index *Index, oldFormat bool, err error) error) error {
+
+	debug.Log("Start")
+
+	type FileInfo struct {
+		restic.ID
+		Size int64
+	}
+
+	var m sync.Mutex
+
+	// track spawned goroutines using wg, create a new context which is
+	// cancelled as soon as an error occurs.
+	wg, ctx := errgroup.WithContext(ctx)
+
+	ch := make(chan FileInfo)
+	// send list of index files through ch, which is closed afterwards
+	wg.Go(func() error {
+		defer close(ch)
+		return repo.List(ctx, restic.IndexFile, func(id restic.ID, size int64) error {
+			select {
+			case <-ctx.Done():
+				return nil
+			case ch <- FileInfo{id, size}:
+			}
+			return nil
+		})
+	})
+
+	// a worker receives an index ID from ch, loads the index, and sends it to indexCh
+	worker := func() error {
+		var buf []byte
+		for fi := range ch {
+			debug.Log("worker got file %v", fi.ID.Str())
+			var err error
+			var idx *Index
+			oldFormat := false
+
+			buf, err = repo.LoadAndDecrypt(ctx, buf[:0], restic.IndexFile, fi.ID)
+			if err == nil {
+				idx, oldFormat, err = DecodeIndex(buf, fi.ID)
+			}
+
+			m.Lock()
+			err = fn(fi.ID, idx, oldFormat, err)
+			m.Unlock()
+			if err != nil {
+				return err
+			}
+		}
+		return nil
+	}
+
+	// run workers on ch
+	wg.Go(func() error {
+		return RunWorkers(loadIndexParallelism, worker)
+	})
+
+	return wg.Wait()
+}