How to set a timeout for MySQL query using C API

Question

I know there are lots of similar questions here, also there are lots of results, when I google it, but none of them answers my question. I read this, this, this and this but

Answer 1

I have never tryed to do that, but i've been reading and i think that could means that MYSQL_OPT_WRITE_TIMEOUT and MYSQL_OPT_READ_TIMEOUT are only for windows prior MySQL version 5.0.25 but now sould be working for every TCP/IP connection. Take a look here

Regards

EDIT: I would try to update my mysql server to a newer version and try if it works.

Answer 2

I suppose you could implement a timeout for the C function call (as described in this thread C++: How to implement a timeout for an arbitrary function call?), but you would need to think carefully about what kind of state you would leave the DB in - presumably these are just for reads of the database, not inserts/updates.

Answer 3

If you don't mind using threads, you could start the query from a new thread and have the main thread perform a short pthread_cond_timedwait for the new thread to set a condition variable that it make the connection. Then you can let the thread linger around until the actual mysql call times out. Just make sure it's detached so its resources get freed when it finally does time out. This solution isn't pretty, but it should at least work.

Answer 4

Okay, I found a solution.. Thanks to Will and PRR( my co-worker ).

I cannot start a new thread on each query, as this is a real-time application, that is supposed to process 1000+ messages per second..(anyway, thanks to R.. for the idea).

Also, it was not possible to terminate the connection through the library, nor to cancel/kill the query, as the problem was in the DB server..

And here's a brute-force solution, but still much better that _EXIT( FAILURE ): Here's the related question: "How to force closing socket on Linux?" - so, I just closed the socket using a system call.

Important NOTE: (thanks Will) - It turned out, that our MySQL library wrapper has s "fail-safe" flag, so that on closed socket (or other critical error), it tries to "solve" the problem, so it reopens the socket, by itself, in my case. So, I just turned off this option and everything is fine now - the execute is terminated because of an exception - this is the "softest" way to do this.
This should be done through another thread, of course - a timer, for example.

EDIT: The timeouts are really working for versions after 5.0.25. But, at least on RHEL4 and RHEL5, the timeouts are tripled for some reason! For example, if some of the timeouts is set to 20sec, the real timeout is ~60sec..
Also, another important thing is, that these timeouts(as any other options) MUST be set after mysql_init and before mysql_connect or mysql_real_connect.