ui-repolist: implement lazy caching of repo->mtime

When sorting the list of repositories by their last modification time,
cgit would (in the worst case) invoke fstat(3) four times and open(3)
twice for each callback from qsort(3). This obviously scales very badly.

Now, the calculated modtime for each repo is saved in repo->mtime, thus
keeping the number of stat/open invocations identical for sorted and
unsorted repo-listings.

Signed-off-by: Lars Hjemli <hjemli@gmail.com>

3 files changed, 14 insertions, 4 deletions

diff --git a/cgit.h b/cgit.h
index ea90833..c99d337 100644
--- a/cgit.h
+++ b/cgit.h
@@ -48,32 +48,33 @@ typedef void (*filepair_fn)(struct diff_filepair *pair);
 typedef void (*linediff_fn)(char *line, int len);
 
 struct cgit_repo {
 	char *url;
 	char *name;
 	char *path;
 	char *desc;
 	char *owner;
 	char *defbranch;
 	char *group;
 	char *module_link;
 	char *readme;
 	char *clone_url;
 	int snapshots;
 	int enable_log_filecount;
 	int enable_log_linecount;
+	time_t mtime;
 };
 
 struct cgit_repolist {
 	int length;
 	int count;
 	struct cgit_repo *repos;
 };
 
 struct commitinfo {
 	struct commit *commit;
 	char *author;
 	char *author_email;
 	unsigned long author_date;
 	char *committer;
 	char *committer_email;
 	unsigned long committer_date;
diff --git a/shared.c b/shared.c
index f5875e4..89d1bab 100644
--- a/shared.c
+++ b/shared.c
@@ -47,32 +47,33 @@ struct cgit_repo *cgit_add_repo(const char *url)
 					       sizeof(struct cgit_repo));
 	}
 
 	ret = &cgit_repolist.repos[cgit_repolist.count-1];
 	ret->url = trim_end(url, '/');
 	ret->name = ret->url;
 	ret->path = NULL;
 	ret->desc = "[no description]";
 	ret->owner = NULL;
 	ret->group = ctx.cfg.repo_group;
 	ret->defbranch = "master";
 	ret->snapshots = ctx.cfg.snapshots;
 	ret->enable_log_filecount = ctx.cfg.enable_log_filecount;
 	ret->enable_log_linecount = ctx.cfg.enable_log_linecount;
 	ret->module_link = ctx.cfg.module_link;
 	ret->readme = NULL;
+	ret->mtime = -1;
 	return ret;
 }
 
 struct cgit_repo *cgit_get_repoinfo(const char *url)
 {
 	int i;
 	struct cgit_repo *repo;
 
 	for (i=0; i<cgit_repolist.count; i++) {
 		repo = &cgit_repolist.repos[i];
 		if (!strcmp(repo->url, url))
 			return repo;
 	}
 	return NULL;
 }
 
diff --git a/ui-repolist.c b/ui-repolist.c
index cf27cb3..aa743bf 100644
--- a/ui-repolist.c
+++ b/ui-repolist.c
@@ -19,45 +19,53 @@ time_t read_agefile(char *path)
 
 	if (!(f = fopen(path, "r")))
 		return -1;
 	if (fgets(buf, sizeof(buf), f) == NULL)
 		return -1;
 	fclose(f);
 	if (parse_date(buf, buf2, sizeof(buf2)))
 		return strtoul(buf2, NULL, 10);
 	else
 		return 0;
 }
 
 static int get_repo_modtime(const struct cgit_repo *repo, time_t *mtime)
 {
 	char *path;
 	struct stat s;
+	struct cgit_repo *r = (struct cgit_repo *)repo;
 
+	if (repo->mtime != -1) {
+		*mtime = repo->mtime;
+		return 1;
+	}
 	path = fmt("%s/%s", repo->path, ctx.cfg.agefile);
 	if (stat(path, &s) == 0) {
 		*mtime = read_agefile(path);
+		r->mtime = *mtime;
 		return 1;
 	}
 
 	path = fmt("%s/refs/heads/%s", repo->path, repo->defbranch);
-	if (stat(path, &s) == 0) {
+	if (stat(path, &s) == 0)
 		*mtime = s.st_mtime;
-		return 1;
-	}
-	return 0;
+	else
+		*mtime = 0;
+
+	r->mtime = *mtime;
+	return (r->mtime != 0);
 }
 
 static void print_modtime(struct cgit_repo *repo)
 {
 	time_t t;
 	if (get_repo_modtime(repo, &t))
 		cgit_print_age(t, -1, NULL);
 }
 
 int is_match(struct cgit_repo *repo)
 {
 	if (!ctx.qry.search)
 		return 1;
 	if (repo->url && strcasestr(repo->url, ctx.qry.search))
 		return 1;
 	if (repo->name && strcasestr(repo->name, ctx.qry.search))