Merge pull request #579 from erizocosmico/perf/revlist-no-revisit-ancestors

revlist: do not visit again already visited parents

Author: mcuadros

plumbing/revlist/revlist.go

@@ -35,9 +35,9 @@ func objects(
 	ignore []plumbing.Hash,
 	allowMissingObjects bool,
 ) ([]plumbing.Hash, error) {
-
 	seen := hashListToSet(ignore)
 	result := make(map[plumbing.Hash]bool)
+	visited := make(map[plumbing.Hash]bool)
 
 	walkerFunc := func(h plumbing.Hash) {
 		if !seen[h] {
@@ -47,7 +47,7 @@ func objects(
 	}
 
 	for _, h := range objects {
-		if err := processObject(s, h, seen, ignore, walkerFunc); err != nil {
+		if err := processObject(s, h, seen, visited, ignore, walkerFunc); err != nil {
 			if allowMissingObjects && err == plumbing.ErrObjectNotFound {
 				continue
 			}
@@ -64,6 +64,7 @@ func processObject(
 	s storer.EncodedObjectStorer,
 	h plumbing.Hash,
 	seen map[plumbing.Hash]bool,
+	visited map[plumbing.Hash]bool,
 	ignore []plumbing.Hash,
 	walkerFunc func(h plumbing.Hash),
 ) error {
@@ -83,12 +84,12 @@ func processObject(
 
 	switch do := do.(type) {
 	case *object.Commit:
-		return reachableObjects(do, seen, ignore, walkerFunc)
+		return reachableObjects(do, seen, visited, ignore, walkerFunc)
 	case *object.Tree:
 		return iterateCommitTrees(seen, do, walkerFunc)
 	case *object.Tag:
 		walkerFunc(do.Hash)
-		return processObject(s, do.Target, seen, ignore, walkerFunc)
+		return processObject(s, do.Target, seen, visited, ignore, walkerFunc)
 	case *object.Blob:
 		walkerFunc(do.Hash)
 	default:
@@ -103,34 +104,60 @@ func processObject(
 // objects from the specified commit. To avoid to iterate over seen commits,
 // if a commit hash is into the 'seen' set, we will not iterate all his trees
 // and blobs objects.
+// We assume all commits have the same parents, unless a commit has no parents.
+// So when we've visited a commit before, we can stop iterating commits, as we've
+// already processed all its ancestors before as well. `visited` keeps track of
+// all the commits that have been visited that had parents.
 func reachableObjects(
 	commit *object.Commit,
 	seen map[plumbing.Hash]bool,
+	visited map[plumbing.Hash]bool,
 	ignore []plumbing.Hash,
-	cb func(h plumbing.Hash)) error {
-
+	cb func(h plumbing.Hash),
+) error {
 	i := object.NewCommitPreorderIter(commit, ignore)
-	return i.ForEach(func(commit *object.Commit) error {
+	for {
+		commit, err := i.Next()
+		if err == io.EOF {
+			break
+		}
+
+		if err != nil {
+			return err
+		}
+
+		if visited[commit.Hash] {
+			break
+		}
+
 		if seen[commit.Hash] {
-			return nil
+			continue
 		}
 
 		cb(commit.Hash)
+		if commit.NumParents() > 0 {
+			visited[commit.Hash] = true
+		}
 
 		tree, err := commit.Tree()
 		if err != nil {
 			return err
 		}
 
-		return iterateCommitTrees(seen, tree, cb)
-	})
+		if err := iterateCommitTrees(seen, tree, cb); err != nil {
+			return err
+		}
+	}
+
+	return nil
 }
 
 // iterateCommitTrees iterate all reachable trees from the given commit
 func iterateCommitTrees(
 	seen map[plumbing.Hash]bool,
 	tree *object.Tree,
-	cb func(h plumbing.Hash)) error {
+	cb func(h plumbing.Hash),
+) error {
 	if seen[tree.Hash] {
 		return nil
 	}