1 files changed, 156 insertions, 0 deletions
diff --git a/src/lib-sql/sql-db-cache.c b/src/lib-sql/sql-db-cache.c
new file mode 100644
index 0000000..b2fb9fb
--- /dev/null
+++ b/src/lib-sql/sql-db-cache.c
@@ -0,0 +1,156 @@
+/* Copyright (c) 2004-2018 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+#include "array.h"
+#include "hash.h"
+#include "sql-api-private.h"
+#include "sql-db-cache.h"
+
+#define SQL_DB_CACHE_CONTEXT(obj) \
+	MODULE_CONTEXT_REQUIRE(obj, sql_db_cache_module)
+
+struct sql_db_cache_context {
+	union sql_db_module_context module_ctx;
+	struct sql_db *prev, *next; /* These are set while refcount=0 */
+
+	struct sql_db_cache *cache;
+	int refcount;
+	char *key;
+	void (*orig_deinit)(struct sql_db *db);
+};
+
+struct sql_db_cache {
+	HASH_TABLE(char *, struct sql_db *) dbs;
+	unsigned int unused_count, max_unused_connections;
+	struct sql_db *unused_tail, *unused_head;
+};
+
+static MODULE_CONTEXT_DEFINE_INIT(sql_db_cache_module, &sql_db_module_register);
+
+static void sql_db_cache_db_unref(struct sql_db *db)
+{
+	struct sql_db_cache_context *ctx = SQL_DB_CACHE_CONTEXT(db);
+	struct sql_db_cache_context *head_ctx;
+
+	if (--ctx->refcount > 0)
+		return;
+
+	i_assert(db->refcount == 2);
+
+	ctx->cache->unused_count++;
+	if (ctx->cache->unused_tail == NULL)
+		ctx->cache->unused_tail = db;
+	else {
+		head_ctx = SQL_DB_CACHE_CONTEXT(ctx->cache->unused_head);
+		head_ctx->next = db;
+	}
+	ctx->prev = ctx->cache->unused_head;
+	ctx->cache->unused_head = db;
+}
+
+static void sql_db_cache_unlink(struct sql_db_cache_context *ctx)
+{
+	struct sql_db_cache_context *prev_ctx, *next_ctx;
+
+	i_assert(ctx->refcount == 0);
+
+	if (ctx->prev == NULL)
+		ctx->cache->unused_tail = ctx->next;
+	else {
+		prev_ctx = SQL_DB_CACHE_CONTEXT(ctx->prev);
+		prev_ctx->next = ctx->next;
+	}
+	if (ctx->next == NULL)
+		ctx->cache->unused_head = ctx->prev;
+	else {
+		next_ctx = SQL_DB_CACHE_CONTEXT(ctx->next);
+		next_ctx->prev = ctx->prev;
+	}
+	ctx->cache->unused_count--;
+}
+
+static void sql_db_cache_free_tail(struct sql_db_cache *cache)
+{
+	struct sql_db *db;
+	struct sql_db_cache_context *ctx;
+
+	db = cache->unused_tail;
+	i_assert(db->refcount == 1);
+
+	ctx = SQL_DB_CACHE_CONTEXT(db);
+	sql_db_cache_unlink(ctx);
+	hash_table_remove(cache->dbs, ctx->key);
+
+	i_free(ctx->key);
+	i_free(ctx);
+
+	db->v.unref = NULL;
+	sql_unref(&db);
+}
+
+static void sql_db_cache_drop_oldest(struct sql_db_cache *cache)
+{
+	while (cache->unused_count >= cache->max_unused_connections)
+		sql_db_cache_free_tail(cache);
+}
+
+int sql_db_cache_new(struct sql_db_cache *cache, const struct sql_settings *set,
+		     struct sql_db **db_r, const char **error_r)
+{
+	struct sql_db_cache_context *ctx;
+	struct sql_db *db;
+	char *key;
+
+	key = i_strdup_printf("%s\t%s", set->driver, set->connect_string);
+	db = hash_table_lookup(cache->dbs, key);
+	if (db != NULL) {
+		ctx = SQL_DB_CACHE_CONTEXT(db);
+		if (ctx->refcount == 0) {
+			sql_db_cache_unlink(ctx);
+			ctx->prev = ctx->next = NULL;
+		}
+		i_free(key);
+	} else {
+		sql_db_cache_drop_oldest(cache);
+
+		if (sql_init_full(set, &db, error_r) < 0) {
+			i_free(key);
+			return -1;
+		}
+
+		ctx = i_new(struct sql_db_cache_context, 1);
+		ctx->cache = cache;
+		ctx->key = key;
+		ctx->orig_deinit = db->v.deinit;
+		db->v.unref = sql_db_cache_db_unref;
+
+		MODULE_CONTEXT_SET(db, sql_db_cache_module, ctx);
+		hash_table_insert(cache->dbs, ctx->key, db);
+	}
+
+	ctx->refcount++;
+	sql_ref(db);
+	*db_r = db;
+	return 0;
+}
+
+struct sql_db_cache *sql_db_cache_init(unsigned int max_unused_connections)
+{
+	struct sql_db_cache *cache;
+
+	cache = i_new(struct sql_db_cache, 1);
+	hash_table_create(&cache->dbs, default_pool, 0, str_hash, strcmp);
+	cache->max_unused_connections = max_unused_connections;
+	return cache;
+}
+
+void sql_db_cache_deinit(struct sql_db_cache **_cache)
+{
+	struct sql_db_cache *cache = *_cache;
+
+	*_cache = NULL;
+	while (cache->unused_tail != NULL)
+		sql_db_cache_free_tail(cache);
+	hash_table_destroy(&cache->dbs);
+	i_free(cache);
+}