On open repository open common cat file batch and batch-check (#15667)

Use common git cat-file --batch and git cat-file --batch-check to
significantly reduce calls to git.
    
Signed-off-by: Andrew Thornton <art27@cantab.net>

modules/git/repo_base_nogogit.go

@@ -8,6 +8,8 @@
 package git
 
 import (
+	"bufio"
+	"context"
 	"errors"
 	"path/filepath"
 )
@@ -19,6 +21,14 @@ type Repository struct {
 	tagCache *ObjectCache
 
 	gpgSettings *GPGSettings
+
+	batchCancel context.CancelFunc
+	batchReader *bufio.Reader
+	batchWriter WriteCloserError
+
+	checkCancel context.CancelFunc
+	checkReader *bufio.Reader
+	checkWriter WriteCloserError
 }
 
 // OpenRepository opens the repository at the given path.
@@ -29,12 +39,51 @@ func OpenRepository(repoPath string) (*Repository, error) {
 	} else if !isDir(repoPath) {
 		return nil, errors.New("no such file or directory")
 	}
-	return &Repository{
+
+	repo := &Repository{
 		Path:     repoPath,
 		tagCache: newObjectCache(),
-	}, nil
+	}
+
+	repo.batchWriter, repo.batchReader, repo.batchCancel = CatFileBatch(repoPath)
+	repo.checkWriter, repo.checkReader, repo.checkCancel = CatFileBatchCheck(repo.Path)
+
+	return repo, nil
+}
+
+// CatFileBatch obtains a CatFileBatch for this repository
+func (repo *Repository) CatFileBatch() (WriteCloserError, *bufio.Reader, func()) {
+	if repo.batchCancel == nil || repo.batchReader.Buffered() > 0 {
+		log("Opening temporary cat file batch for: %s", repo.Path)
+		return CatFileBatch(repo.Path)
+	}
+	return repo.batchWriter, repo.batchReader, func() {}
+}
+
+// CatFileBatchCheck obtains a CatFileBatchCheck for this repository
+func (repo *Repository) CatFileBatchCheck() (WriteCloserError, *bufio.Reader, func()) {
+	if repo.checkCancel == nil || repo.checkReader.Buffered() > 0 {
+		log("Opening temporary cat file batch-check: %s", repo.Path)
+		return CatFileBatchCheck(repo.Path)
+	}
+	return repo.checkWriter, repo.checkReader, func() {}
 }
 
 // Close this repository, in particular close the underlying gogitStorage if this is not nil
 func (repo *Repository) Close() {
+	if repo == nil {
+		return
+	}
+	if repo.batchCancel != nil {
+		repo.batchCancel()
+		repo.batchReader = nil
+		repo.batchWriter = nil
+		repo.batchCancel = nil
+	}
+	if repo.checkCancel != nil {
+		repo.checkCancel()
+		repo.checkCancel = nil
+		repo.checkReader = nil
+		repo.checkWriter = nil
+	}
 }