src/timer/SDL_timer.c

/*
    SDL - Simple DirectMedia Layer
    Copyright (C) 1997-2010 Sam Lantinga

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
    License as published by the Free Software Foundation; either
    version 2.1 of the License, or (at your option) any later version.

    This library 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
    Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public
    License along with this library; if not, write to the Free Software
    Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA

    Sam Lantinga
    slouken@libsdl.org
*/
#include "SDL_config.h"

#include "SDL_timer.h"
#include "SDL_timer_c.h"
#include "SDL_mutex.h"
#include "SDL_systimer.h"

/* #define DEBUG_TIMERS */

int SDL_timer_started = 0;
int SDL_timer_running = 0;

/* Data to handle a single periodic alarm */
Uint32 SDL_alarm_interval = 0;
SDL_TimerCallback SDL_alarm_callback;

/* Data used for a thread-based timer */
static int SDL_timer_threaded = 0;

struct _SDL_TimerID
{
    Uint32 interval;
    SDL_NewTimerCallback cb;
    void *param;
    Uint32 last_alarm;
    struct _SDL_TimerID *next;
};

static SDL_TimerID SDL_timers = NULL;
static SDL_mutex *SDL_timer_mutex;
static volatile SDL_bool list_changed = SDL_FALSE;

/* Set whether or not the timer should use a thread.
   This should not be called while the timer subsystem is running.
*/
int
SDL_SetTimerThreaded(int value)
{
    int retval;

    if (SDL_timer_started) {
        SDL_SetError("Timer already initialized");
        retval = -1;
    } else {
        retval = 0;
        SDL_timer_threaded = value;
    }
    return retval;
}

int
SDL_TimerInit(void)
{
    int retval;

    retval = 0;
    if (SDL_timer_started) {
        SDL_TimerQuit();
    }
    if (!SDL_timer_threaded) {
        retval = SDL_SYS_TimerInit();
    }
    if (SDL_timer_threaded) {
        SDL_timer_mutex = SDL_CreateMutex();
    }
    if (retval == 0) {
        SDL_timer_started = 1;
    }
    return (retval);
}

void
SDL_TimerQuit(void)
{
    SDL_SetTimer(0, NULL);
    if (SDL_timer_threaded < 2) {
        SDL_SYS_TimerQuit();
    }
    if (SDL_timer_threaded) {
        SDL_DestroyMutex(SDL_timer_mutex);
        SDL_timer_mutex = NULL;
    }
    SDL_timer_started = 0;
    SDL_timer_threaded = 0;
}

void
SDL_ThreadedTimerCheck(void)
{
    Uint32 now, ms;
    SDL_TimerID t, prev, next;
    SDL_bool removed;

    SDL_mutexP(SDL_timer_mutex);

    now = SDL_GetTicks();
    do {
        list_changed = SDL_FALSE;
        for (prev = NULL, t = SDL_timers; t; t = next) {
            removed = SDL_FALSE;
            ms = t->interval - SDL_TIMESLICE;
            next = t->next;
            if ((int) (now - t->last_alarm) > (int) ms) {
                struct _SDL_TimerID timer;

                if ((now - t->last_alarm) < t->interval) {
                    t->last_alarm += t->interval;
                } else {
                    t->last_alarm = now;
                }
#ifdef DEBUG_TIMERS
                printf("Executing timer %p (thread = %lu)\n",
                       t, SDL_ThreadID());
#endif
                timer = *t;
                SDL_mutexV(SDL_timer_mutex);
                ms = timer.cb(timer.interval, timer.param);
                SDL_mutexP(SDL_timer_mutex);
                if (list_changed) {
                    next = t->next;
                    for (prev = SDL_timers; prev; prev = prev->next) {
                        if (prev->next == t)
                            break;
                    }
                }
                if (ms != t->interval) {
                    if (ms) {
                        t->interval = ROUND_RESOLUTION(ms);
                    } else {
                        /* Remove timer from the list */
#ifdef DEBUG_TIMERS
                        printf("SDL: Removing timer %p\n", t);
#endif
                        if (prev) {
                            prev->next = next;
                        } else {
                            SDL_timers = next;
                        }
                        SDL_free(t);
                        --SDL_timer_running;
                        removed = SDL_TRUE;
                    }
                }
                if (list_changed) {
                    /* Abort, list of timers modified */
                    break;
                }
            }
            /* Don't update prev if the timer has disappeared */
            if (!removed) {
                prev = t;
            }
        }
    } while (list_changed);

    SDL_mutexV(SDL_timer_mutex);
}

static SDL_TimerID
SDL_AddTimerInternal(Uint32 interval, SDL_NewTimerCallback callback,
                     void *param)
{
    SDL_TimerID t;
    t = (SDL_TimerID) SDL_malloc(sizeof(struct _SDL_TimerID));
    if (t) {
        t->interval = ROUND_RESOLUTION(interval);
        t->cb = callback;
        t->param = param;
        t->last_alarm = SDL_GetTicks();
        t->next = SDL_timers;
        SDL_timers = t;
        ++SDL_timer_running;
        list_changed = SDL_TRUE;
    }
#ifdef DEBUG_TIMERS
    printf("SDL_AddTimer(%d) = %08x num_timers = %d\n", interval, (Uint32) t,
           SDL_timer_running);
#endif
    return t;
}

SDL_TimerID
SDL_AddTimer(Uint32 interval, SDL_NewTimerCallback callback, void *param)
{
    SDL_TimerID t;
    if (!SDL_timer_mutex) {
        if (SDL_timer_started) {
            SDL_SetError("This platform doesn't support multiple timers");
        } else {
            SDL_SetError("You must call SDL_Init(SDL_INIT_TIMER) first");
        }
        return NULL;
    }
    if (!SDL_timer_threaded) {
        SDL_SetError("Multiple timers require threaded events!");
        return NULL;
    }
    SDL_mutexP(SDL_timer_mutex);
    t = SDL_AddTimerInternal(interval, callback, param);
    SDL_mutexV(SDL_timer_mutex);
    return t;
}

SDL_bool
SDL_RemoveTimer(SDL_TimerID id)
{
    SDL_TimerID t, prev = NULL;
    SDL_bool removed;

    removed = SDL_FALSE;
    SDL_mutexP(SDL_timer_mutex);
    /* Look for id in the linked list of timers */
    for (t = SDL_timers; t; prev = t, t = t->next) {
        if (t == id) {
            if (prev) {
                prev->next = t->next;
            } else {
                SDL_timers = t->next;
            }
            SDL_free(t);
            --SDL_timer_running;
            removed = SDL_TRUE;
            list_changed = SDL_TRUE;
            break;
        }
    }
#ifdef DEBUG_TIMERS
    printf("SDL_RemoveTimer(%08x) = %d num_timers = %d thread = %lu\n",
           (Uint32) id, removed, SDL_timer_running, SDL_ThreadID());
#endif
    SDL_mutexV(SDL_timer_mutex);
    return removed;
}

/* Old style callback functions are wrapped through this */
static Uint32 SDLCALL
callback_wrapper(Uint32 ms, void *param)
{
    SDL_TimerCallback func = (SDL_TimerCallback) param;
    return (*func) (ms);
}

int
SDL_SetTimer(Uint32 ms, SDL_TimerCallback callback)
{
    int retval;

#ifdef DEBUG_TIMERS
    printf("SDL_SetTimer(%d)\n", ms);
#endif
    retval = 0;

    if (SDL_timer_threaded) {
        SDL_mutexP(SDL_timer_mutex);
    }
    if (SDL_timer_running) {    /* Stop any currently running timer */
        if (SDL_timer_threaded) {
            while (SDL_timers) {
                SDL_TimerID freeme = SDL_timers;
                SDL_timers = SDL_timers->next;
                SDL_free(freeme);
            }
            SDL_timer_running = 0;
            list_changed = SDL_TRUE;
        } else {
            SDL_SYS_StopTimer();
            SDL_timer_running = 0;
        }
    }
    if (ms) {
        if (SDL_timer_threaded) {
            if (SDL_AddTimerInternal
                (ms, callback_wrapper, (void *) callback) == NULL) {
                retval = -1;
            }
        } else {
            SDL_timer_running = 1;
            SDL_alarm_interval = ms;
            SDL_alarm_callback = callback;
            retval = SDL_SYS_StartTimer();
        }
    }
    if (SDL_timer_threaded) {
        SDL_mutexV(SDL_timer_mutex);
    }

    return retval;
}

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