unixodbc - 在多线程并发设置中使用 unixODBC

Question

我要问并回答这个问题，因为我花了很长时间才弄清楚，我希望答案一开始就在这里。

问题：一个长时间运行的 unixODBC 查询会阻止来自同一应用程序的所有其他查询。

问题是：如何阻止这种情况发生。

Answer 1

答案，以来自 __handles.c 的剪切和粘贴评论的形式——我知道，为什么不是每个人都想从那里开始寻找文档，对吧？

/*
 * 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)
 *
 */

Answer 2

只是对该答案的补充。当前版本的 unixODBC 2.3.0 默认设置为 Threading = 0，因此现在的默认设置是假设驱动程序是线程安全的。在过去的几年里，这是一个冒险的假设，而现在则不然。

Answer 3

如果您的驱动程序支持异步功能，您可以启用它并在异步模式下执行耗时的功能。

应用程序端不需要线程。