Designing a Linux Component to address every request with a notification

I have a 3 components say A,B,C. The control flow is from A to B to C. Component A requests B continuously from different functions to B, it forwards the request to C. The Responses from C are received in B and B forwards them to A. Every request that A sends to B (and B to C) should be associated with response from C to B(B to A). I am planning to have message queue in B to hold requests received from A. and similarly another queue for receiving the response from C. Can any one suggest me how to map the every request associated to response,if i don't receive any response (for any request) from C i am supposed to send default response to A. There can be chance that system generated notifications(no request from A) are received in B(to be fwded to A).

please suggest any other data structure if Message queue is incorrect.

Please let me know if you need any more information.

note: C++ is being used for developement. (no C++11 support)