ocesql.c: use pool of sql variables instead of recreating each time

This drops the amount memory allocation/free to the maximum amount of binding variables used.

A run of 8 seconds doing 5000 DB operations previously had 1,945,796 allocations via new_sql_var() and is now down to 426, reducing instructions and cycles executed in the test case by 20% as well.

Author: GitMensch

dblib/ocesql.c

@@ -1,4 +1,4 @@
-/*
+/*
  * Copyright (C) 2015, 2022 Tokyo System House Co.,Ltd.
  * Copyright (C) 2022-2024 Simon Sobisch
  *
@@ -71,13 +71,13 @@ static SQLVARLIST *_sql_var_lists = NULL;
 static SQLVARLIST *_sql_var_lists_last = NULL;
 static SQLVARLIST *_sql_res_var_lists = NULL;
 static SQLVARLIST *_sql_res_var_lists_last = NULL;
+static SQLVARLIST *_pool_sql_var_list = NULL; // Pool of SQLVARLIST items
 static int _var_lists_length = 0;
 static int _res_var_lists_length = 0;
 static int _occurs_length = 0;
 static int _occurs_iter = 0;
 static int _occurs_is_parent = 0;
 
-
 static void sqlca_initialize(struct sqlca_t *);
 
 /* sql var list */
@@ -491,7 +491,7 @@ _ocesqlConnectMain(struct sqlca_t *st, char *name, char *user, char *passwd, cha
 	int connlen = 0;
 
 	LOG("dbname   = %s\n",name);
-	LOG("user     = %s\n",user);
+	LOG("user	 = %s\n",user);
 	LOG("password = %s\n",passwd);
 	LOG("connname = %s\n",conndbname);
 
@@ -2366,9 +2366,17 @@ reset_sql_var_list(void){
  * <Outline>
  *   埋め込みSQLリスト生成
  */
-static inline SQLVARLIST *
-new_sql_var_list(void){
-	return (SQLVARLIST *)calloc(1, sizeof(SQLVARLIST));
+
+static inline SQLVARLIST *new_sql_var_list(void) {
+	SQLVARLIST *new_item;
+	if (_pool_sql_var_list != NULL) {
+		new_item = _pool_sql_var_list;
+		_pool_sql_var_list = _pool_sql_var_list->next;
+		new_item->next = NULL; // Initialize the item
+	} else {
+		new_item = (SQLVARLIST *)calloc(1, sizeof(SQLVARLIST));
+	}
+	return new_item;
 }
 
 /*
@@ -3261,7 +3269,7 @@ set_varchar_length(int len, char *dest){
 		for(i=0; i<OCDB_VARCHAR_HEADER_BYTE; i++){
 			c = 0xf & (len >> (i*4));
 			dest[OCDB_VARCHAR_HEADER_BYTE-i-1] =
-			     (c>9) ? (c+'A'-10) : (c+'0');
+				 (c>9) ? (c+'A'-10) : (c+'0');
 		}
 	}
 	return;
@@ -3286,17 +3294,38 @@ static void show_sql_var_list(SQLVARLIST *p){
  * <Input>
  *   @SQLVARLIST *
  */
-static void
-clear_sql_var_list(SQLVARLIST *p){
-	if(p != NULL){
-		clear_sql_var_list(p->next);
-		if(p->sv.data)
-			free(p->sv.data);
-		if(p->sv.realdata)
-			free(p->sv.realdata);
-		free(p);
+static void clear_sql_var_list(SQLVARLIST *p) {
+	if (p == NULL)
+		return; // Nothing to clear
+
+	SQLVARLIST *temp = p;
+	SQLVARLIST *last_item = NULL;
+	while (temp != NULL) {
+		SQLVARLIST *next = temp->next;
+		if (temp->sv.data)
+			free(temp->sv.data);
+		if (temp->sv.realdata)
+			free(temp->sv.realdata);
+		// Initialize the item before returning it to the pool
+		memset(&temp->sv, 0, sizeof(SQLVAR));
+		last_item = temp;
+		temp = next;
+	}
+	// Return the entire list to the pool
+	last_item->next = _pool_sql_var_list;
+	_pool_sql_var_list = p;
+}
+
+#if 0
+/* free memory, this shoulkd be called at program exit, currently unused */
+static void cleanup_sql_var_pool(void) {
+	while (_pool_sql_var_list != NULL) {
+		SQLVARLIST *next = _pool_sql_var_list->next;
+		free(_pool_sql_var_list);
+		_pool_sql_var_list = next;
 	}
 }
+#endif
 
 static void
 _ocesqlReleaseConnection(int status, void *arg){