Add a general key-value caching framework

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/cache.c

@@ -0,0 +1,62 @@
+#include <uthash.h>
+
+#include "utils.h"
+#include "cache.h"
+
+struct cache_entry {
+	char *key;
+	void *value;
+	UT_hash_handle hh;
+};
+
+struct cache {
+	cache_getter_t getter;
+	cache_free_t free;
+	void *user_data;
+	struct cache_entry *entries;
+};
+
+void *cache_get(struct cache *c, const char *key) {
+	struct cache_entry *e;
+	HASH_FIND_STR(c->entries, key, e);
+	if (e) {
+		return e->value;
+	}
+
+	e = ccalloc(1, struct cache_entry);
+	e->key = strdup(key);
+	e->value = c->getter(c->user_data, key);
+	HASH_ADD_STR(c->entries, key, e);
+	return e->value;
+}
+
+static inline void _cache_invalidate(struct cache *c, struct cache_entry *e) {
+	if (c->free) {
+		c->free(c->user_data, e->value);
+	}
+	HASH_DEL(c->entries, e);
+	free(e);
+}
+
+void cache_invalidate(struct cache *c, const char *key) {
+	struct cache_entry *e;
+	HASH_FIND_STR(c->entries, key, e);
+
+	if (e) {
+		_cache_invalidate(c, e);
+	}
+}
+
+void cache_invalidate_all(struct cache *c) {
+	struct cache_entry *e, *tmpe;
+	HASH_ITER(hh, c->entries, e, tmpe) {
+		_cache_invalidate(c, e);
+	}
+}
+
+void *cache_free(struct cache *c) {
+	void *ret = c->user_data;
+	cache_invalidate_all(c);
+	free(c);
+	return ret;
+}