attrcache: don't re-read attrs during checkout

During checkout, assume that the .gitattributes files aren't
modified during the checkout.  Instead, create an "attribute session"
during checkout.  Assume that attribute data read in the same
checkout "session" hasn't been modified since the checkout started.
(But allow subsequent checkouts to invalidate the cache.)

Further, cache nonexistent git_attr_file data even when .gitattributes
files are not found to prevent re-scanning for nonexistent files.

1 files changed, 40 insertions, 17 deletions

diff --git a/src/attr_file.c b/src/attr_file.c
index 5b008b0e3..9896df4f9 100644
--- a/src/attr_file.c
+++ b/src/attr_file.c
@@ -96,6 +96,7 @@ static int attr_file_oid_from_index(
 int git_attr_file__load(
 	git_attr_file **out,
 	git_repository *repo,
+	git_attr_session *attr_session,
 	git_attr_file_entry *entry,
 	git_attr_file_source source,
 	git_attr_file_parser parser)
@@ -105,6 +106,7 @@ int git_attr_file__load(
 	git_buf content = GIT_BUF_INIT;
 	git_attr_file *file;
 	struct stat st;
+	bool nonexistent = false;
 
 	*out = NULL;
 
@@ -127,22 +129,16 @@ int git_attr_file__load(
 	case GIT_ATTR_FILE__FROM_FILE: {
 		int fd;
 
-		if (p_stat(entry->fullpath, &st) < 0)
-			return git_path_set_error(errno, entry->fullpath, "stat");
-		if (S_ISDIR(st.st_mode))
-			return GIT_ENOTFOUND;
-
-		/* For open or read errors, return ENOTFOUND to skip item */
+		/* For open or read errors, pretend that we got ENOTFOUND. */
 		/* TODO: issue warning when warning API is available */
 
-		if ((fd = git_futils_open_ro(entry->fullpath)) < 0)
-			return GIT_ENOTFOUND;
-
-		error = git_futils_readbuffer_fd(&content, fd, (size_t)st.st_size);
-		p_close(fd);
-
-		if (error < 0)
-			return GIT_ENOTFOUND;
+		if (p_stat(entry->fullpath, &st) < 0 ||
+			S_ISDIR(st.st_mode) ||
+			(fd = git_futils_open_ro(entry->fullpath)) < 0 ||
+			(error = git_futils_readbuffer_fd(&content, fd, (size_t)st.st_size)) < 0)
+			nonexistent = true;
+		else
+			p_close(fd);
 
 		break;
 	}
@@ -154,13 +150,21 @@ int git_attr_file__load(
 	if ((error = git_attr_file__new(&file, entry, source)) < 0)
 		goto cleanup;
 
+	/* store the key of the attr_reader; don't bother with cache
+	 * invalidation during the same attr reader session.
+	 */
+	if (attr_session)
+		file->session_key = attr_session->key;
+
 	if (parser && (error = parser(repo, file, git_buf_cstr(&content))) < 0) {
 		git_attr_file__free(file);
 		goto cleanup;
 	}
 
-	/* write cache breaker */
-	if (source == GIT_ATTR_FILE__FROM_INDEX)
+	/* write cache breakers */
+	if (nonexistent)
+		file->nonexistent = 1;
+	else if (source == GIT_ATTR_FILE__FROM_INDEX)
 		git_oid_cpy(&file->cache_data.oid, git_blob_id(blob));
 	else if (source == GIT_ATTR_FILE__FROM_FILE)
 		git_futils_filestamp_set_from_stat(&file->cache_data.stamp, &st);
@@ -175,11 +179,22 @@ cleanup:
 	return error;
 }
 
-int git_attr_file__out_of_date(git_repository *repo, git_attr_file *file)
+int git_attr_file__out_of_date(
+	git_repository *repo,
+	git_attr_session *attr_session,
+	git_attr_file *file)
 {
 	if (!file)
 		return 1;
 
+	/* we are never out of date if we just created this data in the same
+	 * attr_session; otherwise, nonexistent files must be invalidated
+	 */
+	if (attr_session && attr_session->key == file->session_key)
+		return 0;
+	else if (file->nonexistent)
+		return 1;
+
 	switch (file->source) {
 	case GIT_ATTR_FILE__IN_MEMORY:
 		return 0;
@@ -831,3 +846,11 @@ void git_attr_rule__free(git_attr_rule *rule)
 	git__free(rule);
 }
 
+int git_attr_session__init(git_attr_session *session, git_repository *repo)
+{
+	assert(repo);
+
+	session->key = git_atomic_inc(&repo->attr_session_key);
+
+	return 0;
+}