SDL/src/timer/SDL_timer.c

/*
  Simple DirectMedia Layer
  Copyright (C) 1997-2024 Sam Lantinga <slouken@libsdl.org>

  This software is provided 'as-is', without any express or implied
  warranty.  In no event will the authors be held liable for any damages
  arising from the use of this software.

  Permission is granted to anyone to use this software for any purpose,
  including commercial applications, and to alter it and redistribute it
  freely, subject to the following restrictions:

  1. The origin of this software must not be misrepresented; you must not
     claim that you wrote the original software. If you use this software
     in a product, an acknowledgment in the product documentation would be
     appreciated but is not required.
  2. Altered source versions must be plainly marked as such, and must not be
     misrepresented as being the original software.
  3. This notice may not be removed or altered from any source distribution.
*/
#include "SDL_internal.h"

#include "SDL_timer_c.h"
#include "../thread/SDL_systhread.h"

// #define DEBUG_TIMERS

#if !defined(SDL_PLATFORM_EMSCRIPTEN) || !defined(SDL_THREADS_DISABLED)

typedef struct SDL_Timer
{
    SDL_TimerID timerID;
    SDL_TimerCallback callback_ms;
    SDL_NSTimerCallback callback_ns;
    void *userdata;
    Uint64 interval;
    Uint64 scheduled;
    SDL_AtomicInt canceled;
    struct SDL_Timer *next;
} SDL_Timer;

typedef struct SDL_TimerMap
{
    SDL_TimerID timerID;
    SDL_Timer *timer;
    struct SDL_TimerMap *next;
} SDL_TimerMap;

// The timers are kept in a sorted list
typedef struct
{
    // Data used by the main thread
    SDL_Thread *thread;
    SDL_TimerMap *timermap;
    SDL_Mutex *timermap_lock;

    // Padding to separate cache lines between threads
    char cache_pad[SDL_CACHELINE_SIZE];

    // Data used to communicate with the timer thread
    SDL_SpinLock lock;
    SDL_Semaphore *sem;
    SDL_Timer *pending;
    SDL_Timer *freelist;
    SDL_AtomicInt active;

    // List of timers - this is only touched by the timer thread
    SDL_Timer *timers;
} SDL_TimerData;

static SDL_TimerData SDL_timer_data;

/* The idea here is that any thread might add a timer, but a single
 * thread manages the active timer queue, sorted by scheduling time.
 *
 * Timers are removed by simply setting a canceled flag
 */

static void SDL_AddTimerInternal(SDL_TimerData *data, SDL_Timer *timer)
{
    SDL_Timer *prev, *curr;

    prev = NULL;
    for (curr = data->timers; curr; prev = curr, curr = curr->next) {
        if (curr->scheduled > timer->scheduled) {
            break;
        }
    }

    // Insert the timer here!
    if (prev) {
        prev->next = timer;
    } else {
        data->timers = timer;
    }
    timer->next = curr;
}

static int SDLCALL SDL_TimerThread(void *_data)
{
    SDL_TimerData *data = (SDL_TimerData *)_data;
    SDL_Timer *pending;
    SDL_Timer *current;
    SDL_Timer *freelist_head = NULL;
    SDL_Timer *freelist_tail = NULL;
    Uint64 tick, now, interval, delay;

    /* Threaded timer loop:
     *  1. Queue timers added by other threads
     *  2. Handle any timers that should dispatch this cycle
     *  3. Wait until next dispatch time or new timer arrives
     */
    for (;;) {
        // Pending and freelist maintenance
        SDL_LockSpinlock(&data->lock);
        {
            // Get any timers ready to be queued
            pending = data->pending;
            data->pending = NULL;

            // Make any unused timer structures available
            if (freelist_head) {
                freelist_tail->next = data->freelist;
                data->freelist = freelist_head;
            }
        }
        SDL_UnlockSpinlock(&data->lock);

        // Sort the pending timers into our list
        while (pending) {
            current = pending;
            pending = pending->next;
            SDL_AddTimerInternal(data, current);
        }
        freelist_head = NULL;
        freelist_tail = NULL;

        // Check to see if we're still running, after maintenance
        if (!SDL_AtomicGet(&data->active)) {
            break;
        }

        // Initial delay if there are no timers
        delay = (Uint64)-1;

        tick = SDL_GetTicksNS();

        // Process all the pending timers for this tick
        while (data->timers) {
            current = data->timers;

            if (tick < current->scheduled) {
                // Scheduled for the future, wait a bit
                delay = (current->scheduled - tick);
                break;
            }

            // We're going to do something with this timer
            data->timers = current->next;

            if (SDL_AtomicGet(&current->canceled)) {
                interval = 0;
            } else {
                if (current->callback_ms) {
                    interval = SDL_MS_TO_NS(current->callback_ms(current->userdata, current->timerID, (Uint32)SDL_NS_TO_MS(current->interval)));
                } else {
                    interval = current->callback_ns(current->userdata, current->timerID, current->interval);
                }
            }

            if (interval > 0) {
                // Reschedule this timer
                current->interval = interval;
                current->scheduled = tick + interval;
                SDL_AddTimerInternal(data, current);
            } else {
                if (!freelist_head) {
                    freelist_head = current;
                }
                if (freelist_tail) {
                    freelist_tail->next = current;
                }
                freelist_tail = current;

                SDL_AtomicSet(&current->canceled, 1);
            }
        }

        // Adjust the delay based on processing time
        now = SDL_GetTicksNS();
        interval = (now - tick);
        if (interval > delay) {
            delay = 0;
        } else {
            delay -= interval;
        }

        /* Note that each time a timer is added, this will return
           immediately, but we process the timers added all at once.
           That's okay, it just means we run through the loop a few
           extra times.
         */
        SDL_WaitSemaphoreTimeoutNS(data->sem, delay);
    }
    return 0;
}

bool SDL_InitTimers(void)
{
    SDL_TimerData *data = &SDL_timer_data;

    if (!SDL_AtomicGet(&data->active)) {
        const char *name = "SDLTimer";
        data->timermap_lock = SDL_CreateMutex();
        if (!data->timermap_lock) {
            return false;
        }

        data->sem = SDL_CreateSemaphore(0);
        if (!data->sem) {
            SDL_DestroyMutex(data->timermap_lock);
            return false;
        }

        SDL_AtomicSet(&data->active, 1);

        // Timer threads use a callback into the app, so we can't set a limited stack size here.
        data->thread = SDL_CreateThread(SDL_TimerThread, name, data);
        if (!data->thread) {
            SDL_QuitTimers();
            return false;
        }
    }
    return true;
}

void SDL_QuitTimers(void)
{
    SDL_TimerData *data = &SDL_timer_data;
    SDL_Timer *timer;
    SDL_TimerMap *entry;

    if (SDL_AtomicCompareAndSwap(&data->active, 1, 0)) { // active? Move to inactive.
        // Shutdown the timer thread
        if (data->thread) {
            SDL_SignalSemaphore(data->sem);
            SDL_WaitThread(data->thread, NULL);
            data->thread = NULL;
        }

        SDL_DestroySemaphore(data->sem);
        data->sem = NULL;

        // Clean up the timer entries
        while (data->timers) {
            timer = data->timers;
            data->timers = timer->next;
            SDL_free(timer);
        }
        while (data->freelist) {
            timer = data->freelist;
            data->freelist = timer->next;
            SDL_free(timer);
        }
        while (data->timermap) {
            entry = data->timermap;
            data->timermap = entry->next;
            SDL_free(entry);
        }

        SDL_DestroyMutex(data->timermap_lock);
        data->timermap_lock = NULL;
    }
}

static SDL_TimerID SDL_CreateTimer(Uint64 interval, SDL_TimerCallback callback_ms, SDL_NSTimerCallback callback_ns, void *userdata)
{
    SDL_TimerData *data = &SDL_timer_data;
    SDL_Timer *timer;
    SDL_TimerMap *entry;

    if (!callback_ms && !callback_ns) {
        SDL_InvalidParamError("callback");
        return 0;
    }

    SDL_LockSpinlock(&data->lock);
    if (!SDL_AtomicGet(&data->active)) {
        if (!SDL_InitTimers()) {
            SDL_UnlockSpinlock(&data->lock);
            return 0;
        }
    }

    timer = data->freelist;
    if (timer) {
        data->freelist = timer->next;
    }
    SDL_UnlockSpinlock(&data->lock);

    if (timer) {
        SDL_RemoveTimer(timer->timerID);
    } else {
        timer = (SDL_Timer *)SDL_malloc(sizeof(*timer));
        if (!timer) {
            return 0;
        }
    }
    timer->timerID = SDL_GetNextObjectID();
    timer->callback_ms = callback_ms;
    timer->callback_ns = callback_ns;
    timer->userdata = userdata;
    timer->interval = interval;
    timer->scheduled = SDL_GetTicksNS() + timer->interval;
    SDL_AtomicSet(&timer->canceled, 0);

    entry = (SDL_TimerMap *)SDL_malloc(sizeof(*entry));
    if (!entry) {
        SDL_free(timer);
        return 0;
    }
    entry->timer = timer;
    entry->timerID = timer->timerID;

    SDL_LockMutex(data->timermap_lock);
    entry->next = data->timermap;
    data->timermap = entry;
    SDL_UnlockMutex(data->timermap_lock);

    // Add the timer to the pending list for the timer thread
    SDL_LockSpinlock(&data->lock);
    timer->next = data->pending;
    data->pending = timer;
    SDL_UnlockSpinlock(&data->lock);

    // Wake up the timer thread if necessary
    SDL_SignalSemaphore(data->sem);

    return entry->timerID;
}

SDL_TimerID SDL_AddTimer(Uint32 interval, SDL_TimerCallback callback, void *userdata)
{
    return SDL_CreateTimer(SDL_MS_TO_NS(interval), callback, NULL, userdata);
}

SDL_TimerID SDL_AddTimerNS(Uint64 interval, SDL_NSTimerCallback callback, void *userdata)
{
    return SDL_CreateTimer(interval, NULL, callback, userdata);
}

SDL_bool SDL_RemoveTimer(SDL_TimerID id)
{
    SDL_TimerData *data = &SDL_timer_data;
    SDL_TimerMap *prev, *entry;
    bool canceled = false;

    if (!id) {
        return SDL_InvalidParamError("id");
    }

    // Find the timer
    SDL_LockMutex(data->timermap_lock);
    prev = NULL;
    for (entry = data->timermap; entry; prev = entry, entry = entry->next) {
        if (entry->timerID == id) {
            if (prev) {
                prev->next = entry->next;
            } else {
                data->timermap = entry->next;
            }
            break;
        }
    }
    SDL_UnlockMutex(data->timermap_lock);

    if (entry) {
        if (!SDL_AtomicGet(&entry->timer->canceled)) {
            SDL_AtomicSet(&entry->timer->canceled, 1);
            canceled = true;
        }
        SDL_free(entry);
    }
    if (canceled) {
        return true;
    } else {
        return SDL_SetError("Timer not found");
    }
}

#else

#include <emscripten/emscripten.h>
#include <emscripten/eventloop.h>

typedef struct SDL_TimerMap
{
    SDL_TimerID timerID;
    int timeoutID;
    Uint64 interval;
    SDL_TimerCallback callback_ms;
    SDL_NSTimerCallback callback_ns;
    void *userdata;
    struct SDL_TimerMap *next;
} SDL_TimerMap;

typedef struct
{
    SDL_TimerMap *timermap;
} SDL_TimerData;

static SDL_TimerData SDL_timer_data;

static void SDL_Emscripten_TimerHelper(void *userdata)
{
    SDL_TimerMap *entry = (SDL_TimerMap *)userdata;
    if (entry->callback_ms) {
        entry->interval = SDL_MS_TO_NS(entry->callback_ms(entry->userdata, entry->timerID, (Uint32)SDL_NS_TO_MS(entry->interval)));
    } else {
        entry->interval = entry->callback_ns(entry->userdata, entry->timerID, entry->interval);
    }
    if (entry->interval > 0) {
        entry->timeoutID = emscripten_set_timeout(&SDL_Emscripten_TimerHelper,
                                                  SDL_NS_TO_MS(entry->interval),
                                                  entry);
    }
}

bool SDL_InitTimers(void)
{
    return true;
}

void SDL_QuitTimers(void)
{
    SDL_TimerData *data = &SDL_timer_data;
    SDL_TimerMap *entry;

    while (data->timermap) {
        entry = data->timermap;
        data->timermap = entry->next;
        SDL_free(entry);
    }
}

static SDL_TimerID SDL_CreateTimer(Uint64 interval, SDL_TimerCallback callback_ms, SDL_NSTimerCallback callback_ns, void *userdata)
{
    SDL_TimerData *data = &SDL_timer_data;
    SDL_TimerMap *entry;

    if (!callback_ms && !callback_ns) {
        SDL_InvalidParamError("callback");
        return 0;
    }

    entry = (SDL_TimerMap *)SDL_malloc(sizeof(*entry));
    if (!entry) {
        return 0;
    }
    entry->timerID = SDL_GetNextObjectID();
    entry->callback_ms = callback_ms;
    entry->callback_ns = callback_ns;
    entry->userdata = userdata;
    entry->interval = interval;

    entry->timeoutID = emscripten_set_timeout(&SDL_Emscripten_TimerHelper,
                                              SDL_NS_TO_MS(entry->interval),
                                              entry);

    entry->next = data->timermap;
    data->timermap = entry;

    return entry->timerID;
}

SDL_TimerID SDL_AddTimer(Uint32 interval, SDL_TimerCallback callback, void *userdata)
{
    return SDL_CreateTimer(SDL_MS_TO_NS(interval), callback, NULL, userdata);
}

SDL_TimerID SDL_AddTimerNS(Uint64 interval, SDL_NSTimerCallback callback, void *userdata)
{
    return SDL_CreateTimer(interval, NULL, callback, userdata);
}

SDL_bool SDL_RemoveTimer(SDL_TimerID id)
{
    SDL_TimerData *data = &SDL_timer_data;
    SDL_TimerMap *prev, *entry;

    if (!id) {
        return SDL_InvalidParamError("id");
    }

    // Find the timer
    prev = NULL;
    for (entry = data->timermap; entry; prev = entry, entry = entry->next) {
        if (entry->timerID == id) {
            if (prev) {
                prev->next = entry->next;
            } else {
                data->timermap = entry->next;
            }
            break;
        }
    }

    if (entry) {
        emscripten_clear_timeout(entry->timeoutID);
        SDL_free(entry);
        return true;
    } else {
        return SDL_SetError("Timer not found");
    }
}

#endif // !defined(SDL_PLATFORM_EMSCRIPTEN) || !SDL_THREADS_DISABLED

static Uint64 tick_start;
static Uint32 tick_numerator_ns;
static Uint32 tick_denominator_ns;
static Uint32 tick_numerator_ms;
static Uint32 tick_denominator_ms;

#if defined(SDL_TIMER_WINDOWS) && !defined(SDL_PLATFORM_XBOXONE) && !defined(SDL_PLATFORM_XBOXSERIES)
#include <mmsystem.h>
#define HAVE_TIME_BEGIN_PERIOD
#endif

static void SDL_SetSystemTimerResolutionMS(int period)
{
#ifdef HAVE_TIME_BEGIN_PERIOD
    static int timer_period = 0;

    if (period != timer_period) {
        if (timer_period) {
            timeEndPeriod((UINT)timer_period);
        }

        timer_period = period;

        if (timer_period) {
            timeBeginPeriod((UINT)timer_period);
        }
    }
#endif // HAVE_TIME_BEGIN_PERIOD
}

static void SDLCALL SDL_TimerResolutionChanged(void *userdata, const char *name, const char *oldValue, const char *hint)
{
    int period;

    // Unless the hint says otherwise, let's have good sleep precision
    if (hint && *hint) {
        period = SDL_atoi(hint);
    } else {
        period = 1;
    }
    if (period || oldValue != hint) {
        SDL_SetSystemTimerResolutionMS(period);
    }
}

void SDL_InitTicks(void)
{
    Uint64 tick_freq;
    Uint32 gcd;

    if (tick_start) {
        return;
    }

    /* If we didn't set a precision, set it high. This affects lots of things
       on Windows besides the SDL timers, like audio callbacks, etc. */
    SDL_AddHintCallback(SDL_HINT_TIMER_RESOLUTION,
                        SDL_TimerResolutionChanged, NULL);

    tick_freq = SDL_GetPerformanceFrequency();
    SDL_assert(tick_freq > 0 && tick_freq <= (Uint64)SDL_MAX_UINT32);

    gcd = SDL_CalculateGCD(SDL_NS_PER_SECOND, (Uint32)tick_freq);
    tick_numerator_ns = (SDL_NS_PER_SECOND / gcd);
    tick_denominator_ns = (Uint32)(tick_freq / gcd);

    gcd = SDL_CalculateGCD(SDL_MS_PER_SECOND, (Uint32)tick_freq);
    tick_numerator_ms = (SDL_MS_PER_SECOND / gcd);
    tick_denominator_ms = (Uint32)(tick_freq / gcd);

    tick_start = SDL_GetPerformanceCounter();
    if (!tick_start) {
        --tick_start;
    }
}

void SDL_QuitTicks(void)
{
    SDL_RemoveHintCallback(SDL_HINT_TIMER_RESOLUTION,
                        SDL_TimerResolutionChanged, NULL);

    SDL_SetSystemTimerResolutionMS(0); // always release our timer resolution request.

    tick_start = 0;
}

Uint64 SDL_GetTicksNS(void)
{
    Uint64 starting_value, value;

    if (!tick_start) {
        SDL_InitTicks();
    }

    starting_value = (SDL_GetPerformanceCounter() - tick_start);
    value = (starting_value * tick_numerator_ns);
    SDL_assert(value >= starting_value);
    value /= tick_denominator_ns;
    return value;
}

Uint64 SDL_GetTicks(void)
{
    Uint64 starting_value, value;

    if (!tick_start) {
        SDL_InitTicks();
    }

    starting_value = (SDL_GetPerformanceCounter() - tick_start);
    value = (starting_value * tick_numerator_ms);
    SDL_assert(value >= starting_value);
    value /= tick_denominator_ms;
    return value;
}

void SDL_Delay(Uint32 ms)
{
    SDL_SYS_DelayNS(SDL_MS_TO_NS(ms));
}

void SDL_DelayNS(Uint64 ns)
{
    Uint64 current_value = SDL_GetTicksNS();
    Uint64 target_value = current_value + ns;

    // Sleep for a short number of cycles
    // We'll use 1 ms as a scheduling timeslice, it's a good value for modern operating systems
    const int SCHEDULING_TIMESLICE_NS = 1 * SDL_NS_PER_MS;
    while (current_value < target_value) {
        Uint64 remaining_ns = (target_value - current_value);
        if (remaining_ns > (SCHEDULING_TIMESLICE_NS + SDL_NS_PER_US)) {
            // Sleep for a short time, less than the scheduling timeslice
            SDL_SYS_DelayNS(SCHEDULING_TIMESLICE_NS - SDL_NS_PER_US);
        } else {
            // Spin for any remaining time
            SDL_CPUPauseInstruction();
        }
        current_value = SDL_GetTicksNS();
    }
}