Reduce stat() calls on multilevel caches

diff --git a/ccache.c b/ccache.c
index 76c47319d7c26e5b656fd6c5beb89d25f31d90d6..b0b38cad6393e2849ddd999aa3a95f83283d0eb1 100644 (file)
--- a/ccache.c
+++ b/ccache.c
@@ -253,6 +253,10 @@ clean_up_tmp_files()
 /*
  * Transform a name to a full path into the cache directory, creating needed
  * sublevels if needed. Caller frees.
+ *
+ * stat() calls can be expensive on the cache, so we both avoid checking a
+ * single path multiple times, and also avoid stat()ing each level in a
+ * many level cache.
  */
 static char *
 get_path_in_cache(const char *name, const char *suffix)
@@ -260,17 +264,32 @@ get_path_in_cache(const char *name, const char *suffix)
        int i;
        char *path;
        char *result;
+       struct stat st;
 
+       /* Form the entire path */
        path = x_strdup(cache_dir);
        for (i = 0; i < nlevels; ++i) {
                char *p = format("%s/%c", path, name[i]);
                free(path);
                path = p;
-               if (create_dir(path) != 0) {
-                       cc_log("Failed to create %s", path);
-                       failed();
+       }
+
+       /* First see if whole path exists, so can avoid directory one-by-one check */
+       if (!(stat(path, &st) == 0
+             && S_ISDIR(st.st_mode))) {
+               free(path);
+               path = x_strdup(cache_dir);
+               for (i = 0; i < nlevels; ++i) {
+                       char *p = format("%s/%c", path, name[i]);
+                       free(path);
+                       path = p;
+                       if (create_dir(path) != 0) {
+                               cc_log("Failed to create %s", path);
+                               failed();
+                       }
                }
        }
+
        result = format("%s/%s%s", path, name + nlevels, suffix);
        free(path);
        return result;