messagebus.c

/**
    messagebus.c: openchronos-ng messaging system

    Copyright (C) 2012 Angelo Arrifano <miknix@gmail.com>
    Copyright (C) 2016 Benjamin Sølberg <benjamin.soelberg@gmail.com>

    http://github.com/BenjaminSoelberg/openchronos-ng-elf

    This file is part of openchronos-ng.

    openchronos-ng is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    openchronos-ng is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
**/

#include "messagebus.h"

/* the message bus */
static struct sys_messagebus *messagebus;

/***************************************************************************
 ************************* THE SYSTEM MESSAGE BUS **************************
 **************************************************************************/
void sys_messagebus_register(void (*callback)(enum sys_message),
                             enum sys_message listens)
{
    struct sys_messagebus **p = &messagebus;

    while (*p) {
        /* Set p to address of next pointer */
        p = &(*p)->next;
    }

    *p = malloc(sizeof(struct sys_messagebus));
    (*p)->next = NULL;
    (*p)->fn = callback;
    (*p)->listens = listens;
}

void sys_messagebus_unregister_all(void (*callback)(enum sys_message))
{
        sys_messagebus_unregister(callback, 0);
}

void sys_messagebus_unregister(void (*callback)(enum sys_message),
                               enum sys_message listens)
{
    struct sys_messagebus *p = messagebus, *pp = NULL;

    while (p) {
        if (p->fn == callback && (listens == 0 || p->listens == listens)) {
            if (!pp) { // If 1. element
                // Remove first element by pointing to the next
                messagebus = p->next;
                // Free element
                free(p);
                // Set current pointer to point to new first element
                p = messagebus;
                // Keep pp the same (NULL)
            } else { // If 2. or later element
                // Remove element by pointing previous to the next
                pp->next = p->next;
                // Free element
                free(p);
                // Set current pointer to point to next element
                p = pp->next;
                // Keep pp the same
            }
        } else {
            // Set pp (previous pointer) to current element
            pp = p;
            // Set p (current pointer) to next element
            p = p->next;
        }
    }
}
void send_events(enum sys_message msg)
{
    struct sys_messagebus *p = messagebus;

    while (p) {
        /* notify listener if he registered for any of these messages */
        enum sys_message filtered_msg = msg & p->listens;
        if (filtered_msg) {
            p->fn(filtered_msg);
        }

        /* move to next */
        p = p->next;
    }
}