Random talk about redis source code onehundredandtwenty

Use of mask , Really ：

/*
 * Helper function to invoke port_associate for the given fd and mask.
 */
static int aeApiAssociate(const char *where, int portfd, int fd, int mask) {
    int events = 0;
    int rv, err;
 
    if (mask & AE_READABLE)
        events |= POLLIN;
    if (mask & AE_WRITABLE)
        events |= POLLOUT;
 
    if (evport_debug)
        fprintf(stderr, "%s: port_associate(%d, 0x%x) = ", where, fd, events);
 
    rv = port_associate(portfd, PORT_SOURCE_FD, fd, events,
        (void *)(uintptr_t)mask);
    err = errno;
 
    if (evport_debug)
        fprintf(stderr, "%d (%s)\n", rv, rv == 0 ? "no error" : strerror(err));
 
    if (rv == -1) {
        fprintf(stderr, "%s: port_associate: %s\n", where, strerror(err));
 
        if (err == EAGAIN)
            fprintf(stderr, "aeApiAssociate: event port limit exceeded.");
    }
 
    return rv;
}
 
static int aeApiAddEvent(aeEventLoop *eventLoop, int fd, int mask) {
    aeApiState *state = eventLoop->apidata;
    int fullmask, pfd;
 
    if (evport_debug)
        fprintf(stderr, "aeApiAddEvent: fd %d mask 0x%x\n", fd, mask);
 
    /*
     * Since port_associate's "events" argument replaces any existing events, we
     * must be sure to include whatever events are already associated when
     * we call port_associate() again.
     */
    fullmask = mask | eventLoop->events[fd].mask;
    pfd = aeApiLookupPending(state, fd);
 
    if (pfd != -1) {
        /*
         * This fd was recently returned from aeApiPoll.  It should be safe to
         * assume that the consumer has processed that poll event, but we play
         * it safer by simply updating pending_mask.  The fd will be
         * re-associated as usual when aeApiPoll is called again.
         */
        if (evport_debug)
            fprintf(stderr, "aeApiAddEvent: adding to pending fd %d\n", fd);
        state->pending_masks[pfd] |= fullmask;
        return 0;
    }
 
    return (aeApiAssociate("aeApiAddEvent", state->portfd, fd, fullmask));
}