check: Cleanup tree loading and switch to use errgroup

The helper methods are now wired up in the Structure method.

internal/checker/checker.go

@@ -316,72 +316,24 @@ type treeJob struct {
 
 // loadTreeWorker loads trees from repo and sends them to out.
 func loadTreeWorker(ctx context.Context, repo restic.Repository,
-	in <-chan restic.ID, out chan<- treeJob,
-	wg *sync.WaitGroup) {
+	in <-chan restic.ID, out chan<- treeJob) {
 
-	defer func() {
-		debug.Log("exiting")
-		wg.Done()
-	}()
+	for treeID := range in {
+		tree, err := repo.LoadTree(ctx, treeID)
+		debug.Log("load tree %v (%v) returned err: %v", tree, treeID, err)
+		job := treeJob{ID: treeID, error: err, Tree: tree}
 
-	var (
-		inCh  = in
-		outCh = out
-		job   treeJob
-	)
-
-	outCh = nil
-	for {
 		select {
 		case <-ctx.Done():
 			return
-
-		case treeID, ok := <-inCh:
-			if !ok {
-				return
-			}
-			debug.Log("load tree %v", treeID)
-
-			tree, err := repo.LoadTree(ctx, treeID)
-			debug.Log("load tree %v (%v) returned err: %v", tree, treeID, err)
-			job = treeJob{ID: treeID, error: err, Tree: tree}
-			outCh = out
-			inCh = nil
-
-		case outCh <- job:
-			debug.Log("sent tree %v", job.ID)
-			outCh = nil
-			inCh = in
+		case out <- job:
 		}
 	}
 }
 
 // checkTreeWorker checks the trees received and sends out errors to errChan.
-func (c *Checker) checkTreeWorker(ctx context.Context, in <-chan treeJob, out chan<- error, wg *sync.WaitGroup) {
-	defer func() {
-		debug.Log("exiting")
-		wg.Done()
-	}()
-
-	var (
-		inCh      = in
-		outCh     = out
-		treeError TreeError
-	)
-
-	outCh = nil
-	for {
-		select {
-		case <-ctx.Done():
-			debug.Log("done channel closed, exiting")
-			return
-
-		case job, ok := <-inCh:
-			if !ok {
-				debug.Log("input channel closed, exiting")
-				return
-			}
-
+func (c *Checker) checkTreeWorker(ctx context.Context, in <-chan treeJob, out chan<- error) {
+	for job := range in {
 		debug.Log("check tree %v (tree %v, err %v)", job.ID, job.Tree, job.error)
 
 		var errs []error
@@ -391,40 +343,29 @@ func (c *Checker) checkTreeWorker(ctx context.Context, in <-chan treeJob, out ch
 			errs = c.checkTree(job.ID, job.Tree)
 		}
 
-			if len(errs) > 0 {
-				debug.Log("checked tree %v: %v errors", job.ID, len(errs))
-				treeError = TreeError{ID: job.ID, Errors: errs}
-				outCh = out
-				inCh = nil
+		if len(errs) == 0 {
+			continue
 		}
-
-		case outCh <- treeError:
+		treeError := TreeError{ID: job.ID, Errors: errs}
+		select {
+		case <-ctx.Done():
+			return
+		case out <- treeError:
 			debug.Log("tree %v: sent %d errors", treeError.ID, len(treeError.Errors))
-			outCh = nil
-			inCh = in
 		}
 	}
 }
 
 func (c *Checker) filterTrees(ctx context.Context, backlog restic.IDs, loaderChan chan<- restic.ID, in <-chan treeJob, out chan<- treeJob) {
-	defer func() {
-		debug.Log("closing output channels")
-		close(loaderChan)
-		close(out)
-	}()
-
 	var (
 		inCh                    = in
-		outCh                   = out
-		loadCh                  = loaderChan
+		outCh                   chan<- treeJob
+		loadCh                  chan<- restic.ID
 		job                     treeJob
 		nextTreeID              restic.ID
 		outstandingLoadTreeJobs = 0
 	)
 
-	outCh = nil
-	loadCh = nil
-
 	for {
 		if loadCh == nil && len(backlog) > 0 {
 			// process last added ids first, that is traverse the tree in depth-first order
@@ -528,8 +469,6 @@ func loadSnapshotTreeIDs(ctx context.Context, repo restic.Repository) (ids resti
 // subtrees are available in the index. errChan is closed after all trees have
 // been traversed.
 func (c *Checker) Structure(ctx context.Context, errChan chan<- error) {
-	defer close(errChan)
-
 	trees, errs := loadSnapshotTreeIDs(ctx, c.repo)
 	debug.Log("need to check %d trees from snapshots, %d errs returned", len(trees), len(errs))
 
@@ -541,18 +480,42 @@ func (c *Checker) Structure(ctx context.Context, errChan chan<- error) {
 		}
 	}
 
-	treeIDChan := make(chan restic.ID)
-	treeJobChan1 := make(chan treeJob)
-	treeJobChan2 := make(chan treeJob)
+	loaderChan := make(chan restic.ID)
+	loadedTreeChan := make(chan treeJob)
+	treeStream := make(chan treeJob)
+
+	wg, ctx := errgroup.WithContext(ctx)
+	var loadTreeWg sync.WaitGroup
 
-	var wg sync.WaitGroup
 	for i := 0; i < defaultParallelism; i++ {
-		wg.Add(2)
-		go loadTreeWorker(ctx, c.repo, treeIDChan, treeJobChan1, &wg)
-		go c.checkTreeWorker(ctx, treeJobChan2, errChan, &wg)
+		loadTreeWg.Add(1)
+		wg.Go(func() error {
+			defer loadTreeWg.Done()
+			loadTreeWorker(ctx, c.repo, loaderChan, loadedTreeChan)
+			return nil
+		})
+	}
+	// close once all loadTreeWorkers have completed
+	wg.Go(func() error {
+		loadTreeWg.Wait()
+		close(loadedTreeChan)
+		return nil
+	})
+
+	defer close(errChan)
+	for i := 0; i < defaultParallelism; i++ {
+		wg.Go(func() error {
+			c.checkTreeWorker(ctx, treeStream, errChan)
+			return nil
+		})
 	}
 
-	c.filterTrees(ctx, trees, treeIDChan, treeJobChan1, treeJobChan2)
+	wg.Go(func() error {
+		defer close(loaderChan)
+		defer close(treeStream)
+		c.filterTrees(ctx, trees, loaderChan, loadedTreeChan, treeStream)
+		return nil
+	})
 
 	wg.Wait()
 }