[Xcb] Best way to manage server responses in a non-blocking way?

[Juan Lao Tebar]

Hi,

I'm Juan Lao, new user in this mail list. I'm glad to meet you, guys.

I'm creating an intermediate layer between the XCB library and the
logic of my program.

- This layer must NOT block the execution of the main program. There
is a function in the layer that, when it's called from the main
program, it reads all the pending events and replies using
xcb_poll_for_event and xcb_poll_for_reply.

- The layer is object-oriented and implements a MVC architecture: you
register "listeners" and, when an event or a reply is received, the
layer calls your listener.

Ok this is, in a very summarized way, how I'm trying to implement it:

### Main program ###

void myEventReceived() {
    printf("an event has been received!");
}

void myReplyReceived() {
    printf("a reply has been received!");
}

int main() {
    layer_eventCallback = myEventReceived;
    layer_replyCallback = myReplyReceived;

    while (true) {
        layer_dispatchResponses();
        sleep(5);
    }
}

### Layer ###

void (*layer_eventCallback)();
void (*layer_replyCallback)();

void layer_dispatchEvents() {
    bool continueChecking = true;

    while (continueChecking) {
        continueChecking = (layer_nextEvent() || layer_nextReply());
    }
}

void layer_nextEvent() {
    xcb_generic_event_t* e = xcb_poll_for_event(layer_connection);

    if (e == NULL) {
        return false;
    }

    layer_eventCallback();
    free(e);
    return true;
}

void layer_nextReply() {
    // Analog as layer_nextEvent(), but using xcb_poll_for_reply
}

####################

So my questions here are:

1) Is this the correct way to read events and replies from the server?
I understand that if I call xcb_poll_for_event when the next response
is a reply, it will return a NULL. But I'm not sure if I will be able
to read the reply using xcb_poll_for_reply after that...

2) I can not find any example of xcb_poll_for_reply on internet. Is
there any documentation about it? I'm not sure about how to implement
layer_nextReply, since in XCB there is no "generic" replies. (maybe
iterating a list of stored cookies doing the propper castings?)

Well, I think that's all. Thank you guys in advance for any kind of
help on this subject :)

Greetings,
Juan Lao.