在多線程的併發設置中使用unixODBC

Question

我會問這個問題並回答這個問題，因爲它花了我一直的時間來弄清楚，我希望答案在這裏開始。

問題：一個長時間運行的unixODBC查詢會阻止來自同一應用程序的所有其他人。

問題：如何防止這種情況發生。

Answer 1

答案以__handles.c的剪切粘貼評論的形式表達 - 我知道，爲什麼不是所有人都認爲要從那裏開始查看文檔，對吧？

/* 
* 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

只是該答案的補充。當前版本的unixODBC 2.3.0默認爲Threading = 0，所以默認現在是假設驅動程序是線程安全的。這在過去的幾年中是一個冒險的假設，而不是現在這麼多。

Answer 3

如果您的驅動程序支持異步功能，則可以啓用它並在異步模式下執行耗時的功能。

應用程序端不需要線程。