unixodbc - 在多线程并发设置中使用unixODBC

Question

我要问和回答这个问题，因为这使我花了很长时间才弄清楚，我希望答案从这里开始。

问题:一个长时间运行的unixODBC查询会阻止同一应用程序中的所有其他查询。

问题是:如何阻止这种情况的发生。

Answer 1

答案以__handles.c中的剪切粘贴评论的形式出现-我知道，为什么每个人都没有想到从那里开始寻找文档，对吗？

/*
 * use just one mutex for all the lists, this avoids any issues
 * with deadlocks, the performance issue should be minimal, if it
 * turns out to be a problem, we can readdress this
 *
 * We also have a mutex to protect the connection pooling code
 *
 * If compiled with thread support the DM allows four different
 * thread strategies
 *
 * Level 0 - Only the DM internal structures are protected
 * the driver is assumed to take care of it's self
 *
 * Level 1 - The driver is protected down to the statement level
 * each statement will be protected, and the same for the connect
 * level for connect functions, note that descriptors are considered
 * equal to statements when it comes to thread protection.
 *
 * Level 2 - The driver is protected at the connection level. only
 * one thread can be in a particular driver at one time
 *
 * Level 3 - The driver is protected at the env level, only one thing
 * at a time.
 *
 * By default the driver open connections with a lock level of 3,
 * this can be changed by adding the line
 *
 * Threading = N
 *
 * to the driver entry in odbcinst.ini, where N is the locking level
 * (0-3)
 *
 */