环境：Linux ＋ oracle 10g ＋ C
方法：多线程环境下对数据库（Pro*C）进行检索，使用游标。
DBReturn ProcHandle::Test (IN string &sRuleID)
{
struct sqlca sqlca; /*define local sqlca for thread-safe */
EXEC SQL WHENEVER SQLERROR GOTO error;
EXEC SQL WHENEVER NOT FOUND GOTO notfound;
EXEC SQL CONTEXT USE :ctx[m_ctx_index];
EXEC SQL BEGIN DECLARE SECTION;
......
EXEC SQL END DECLARE SECTION;
.......
EXEC SQL
DELETE FROM Test WHERE RULEID = :s_RuleID;
EXEC SQL COMMIT;
if(sqlca.sqlcode==0)
{
rv = DB_OK;
return rv;
}
return rv;
error:
rv = sql_error();
return rv;
notfound:
EXEC SQL ROLLBACK;
return DB_NotFound;
}
我们使用多线程来对Test进行并发调用，当并发量达到10w后如果没有 struct sqlca sqlca;这条语句就将会频繁报错误。
错误内容如下（截取关键部分）：
- ORA-01403: no data found
- ORA--1002: Message -1002 not found; product=RDBMS; facility=ORA
- SQL-02114: Invalid SQL Cursor usage: trying to CLOSE a CLOSEd cursor
- ORA--2114: Message -2114 not found; product=RDBMS; facility=ORA
- SQL-02114: Invalid SQL Cursor usage: trying to CLOSE a CLOSEd cursor
- SQL-02114: Invalid SQL Cursor usage: trying to CLOSE a CLOSEd cursor
- SQL-02114: Invalid SQL Cursor usage: trying to CLOSE a CLOSEd cursor
结果分析：
如果不在函数入口处重新定义sqlca，系统将使用系统全局定义的sqlca作为数据库连接域，而这种情况下，在多任务的模式下线程是不安全的，很可能被其他线程close掉。