fixup! Win32: add a cache below mingw's lstat and dirent implementations

The fscache_clear() function used to be O(n^2). But we can easily make
it O(n) instead.

Update fscache_clear to be O(n) instead of O(n^2) by using inter_next
instead of starting from the begining each time with iter_first. While
at it, also disallow rehashing while removing the entries.

This speeds up a simple `git commit -m foo` when fscache is enabled
(because fscache_clear() is called implicitly by preload_index()).

Signed-off-by: Ben Peart <[email protected]>
Signed-off-by: Johannes Schindelin <[email protected]>

Author: Ben Peart

compat/win32/fscache.c

@@ -257,10 +257,13 @@ static void fscache_clear(void)
 {
 	struct hashmap_iter iter;
 	struct fsentry *fse;
-	while ((fse = hashmap_iter_first(&map, &iter))) {
+	hashmap_disallow_rehash(&map, 1);
+	hashmap_iter_init(&map, &iter);
+	while ((fse = hashmap_iter_next(&iter))) {
 		fscache_remove(fse);
 		fsentry_release(fse);
 	}
+	hashmap_disallow_rehash(&map, 0);
 }
 
 /*