Fix cache algorithm loophole

This closes the door for unneccessary calls to cgit_fill_cache().

Noticed by Linus.

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

cache.c

@@ -10,7 +10,7 @@
 
 const int NOLOCK = -1;
 
-int cache_lookup(struct cacheitem *item)
+void cache_prepare(struct cacheitem *item)
 {
 	if (!cgit_query_repo) {
 		item->name = xstrdup(fmt("%s/index.html", cgit_cache_root));
@@ -30,6 +30,10 @@ int cache_lookup(struct cacheitem *item)
 		else
 			item->ttl = cgit_cache_repo_ttl;
 	}
+}
+
+int cache_exist(struct cacheitem *item)
+{
 	if (stat(item->name, &item->st)) {
 		item->st.st_mtime = 0;
 		return 0;

cgit.c

@@ -465,20 +465,20 @@ static void cgit_fill_cache(struct cacheitem *item)
 
 static void cgit_refresh_cache(struct cacheitem *item)
 {
+	cache_prepare(item);
  top:
-	if (!cache_lookup(item)) {
-		if (cache_lock(item)) {
-			cgit_fill_cache(item);
-			cache_unlock(item);
-		} else {
+	if (!cache_exist(item)) {
+		if (!cache_lock(item)) {
 			sched_yield();
 			goto top;
 		}
-	} else if (cache_expired(item)) {
-		if (cache_lock(item)) {
+		if (!cache_exist(item))
 			cgit_fill_cache(item);
-			cache_unlock(item);
-		}
+		cache_unlock(item);
+	} else if (cache_expired(item) && cache_lock(item)) {
+		if (cache_expired(item))
+			cgit_fill_cache(item);
+		cache_unlock(item);
 	}
 }
 

cgit.h

@@ -56,9 +56,10 @@ extern void html_link_close(void);
 
 extern int cgit_read_config(const char *filename, configfn fn);
 
-extern int cache_lookup(struct cacheitem *item);
+extern void cache_prepare(struct cacheitem *item);
 extern int cache_lock(struct cacheitem *item);
 extern int cache_unlock(struct cacheitem *item);
+extern int cache_exist(struct cacheitem *item);
 extern int cache_expired(struct cacheitem *item);
 
 #endif /* CGIT_H */