add database-aware MySQL pooling

src/lib/compiler.cpp

@@ -16,7 +16,7 @@
 
 namespace {
 
-const u64 UCE_UNIT_ABI_VERSION = 10;
+const u64 UCE_UNIT_ABI_VERSION = 11;
 
 struct SharedUnitFilesystemState
 {

src/lib/mysql-connector.cpp

@@ -3,7 +3,7 @@
 #include <stdlib.h>
 #include "mysql-connector.h"
 
-// Same-credential mysql_connect() calls lease one request-local connection.
+// Same-target mysql_connect() calls lease one request-local connection.
 // mysql_disconnect() releases a lease; cleanup_mysql_connections() owns the
 // actual close at request end, including exception/fatal recovery paths.
 static void mysql_register_request_connection(MySQL* db)
@@ -15,8 +15,12 @@ static void mysql_register_request_connection(MySQL* db)
 		connections.push_back(db);
 }
 
-bool MySQL::connect(String host, String username, String password)
+bool MySQL::connect(String host, String username, String password, String database)
 {
+	request_host = host;
+	request_username = username;
+	request_password = password;
+	request_database = database;
 	// Register regardless of outcome: tracking is about the wrapper's
 	// lifetime, not the connection's. disconnect()/~MySQL() unregister.
 	mysql_register_request_connection(this);
@@ -32,7 +36,7 @@ bool MySQL::connect(String host, String username, String password)
 	}
 
 	if (mysql_real_connect((MYSQL*)connection, host.c_str(), username.c_str(), password.c_str(),
-	  NULL, 0, NULL, 0) == NULL)
+	  database == "" ? NULL : database.c_str(), 0, NULL, 0) == NULL)
 	{
 		auto e = mysql_error((MYSQL*)connection);
 		fprintf(stderr, "%s\n", e);
@@ -59,7 +63,17 @@ bool MySQL::connect(String host, String username, String password)
 
 bool MySQL::reset_connection()
 {
-	if(!connection || mysql_reset_connection((MYSQL*)connection) != 0)
+	if(!connection)
+		return(false);
+	MYSQL* mysql = (MYSQL*)connection;
+	String selected_database = mysql->db == NULL ? "" : mysql->db;
+	// RESET CONNECTION deliberately preserves the selected database. An
+	// unqualified lease cannot safely inherit one selected by its prior request.
+	if(request_database == "" && selected_database != "")
+		return(false);
+	if(mysql_reset_connection(mysql) != 0)
+		return(false);
+	if(request_database != "" && selected_database != request_database && mysql_select_db(mysql, request_database.c_str()) != 0)
 		return(false);
 	_preload_next_error_code = 0;
 	affected_rows = 0;

src/lib/mysql-connector.h

@@ -27,10 +27,11 @@ struct MySQL {
 	String request_host;
 	String request_username;
 	String request_password;
+	String request_database;
 
 	std::vector<MySQLFieldInfo> field_info;
 
-	bool connect(String host = "localhost", String username = "root", String password = "");
+	bool connect(String host = "localhost", String username = "root", String password = "", String database = "");
 	bool reset_connection();
 	void disconnect();
 	String error();
@@ -46,14 +47,14 @@ struct MySQL {
 
 };
 
-inline MySQL* mysql_connect(String host = "localhost", String username = "root", String password = "")
+inline MySQL* mysql_connect(String host = "localhost", String username = "root", String password = "", String database = "")
 {
 	if(context)
 	{
 		for(void* raw : context->resources.mysql_connections)
 		{
 			MySQL* db = (MySQL*)raw;
-			if(db && db->request_pooled && db->connection && db->request_host == host && db->request_username == username && db->request_password == password)
+			if(db && db->request_pooled && db->connection && db->request_host == host && db->request_username == username && db->request_password == password && db->request_database == database)
 			{
 				db->request_leases++;
 				return(db);
@@ -67,7 +68,8 @@ inline MySQL* mysql_connect(String host = "localhost", String username = "root",
 	db->request_host = host;
 	db->request_username = username;
 	db->request_password = password;
-	db->connect(host, username, password);
+	db->request_database = database;
+	db->connect(host, username, password, database);
 	return(db);
 }