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Improved timer implementation
The new timer model is formalized as using a separate thread to handle timer callbacks.  This was the case on almost every platform before, but it's now a requirement, and simplifies the implementation and makes it perform consistently across platforms.

Goals:
 * Minimize timer thread blocking
 * Dispatch timers as accurately as possible
 * SDL_AddTimer() and SDL_RemoveTimer() are completely threadsafe
 * SDL_RemoveTimer() doesn't crash with a timer that's expired or removed
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slouken committed Jan 27, 2011
1 parent 101bb6f commit dc76b82
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Showing 13 changed files with 378 additions and 832 deletions.
7 changes: 7 additions & 0 deletions include/SDL_compat.h
Expand Up @@ -344,6 +344,13 @@ typedef SDL_Window* SDL_WindowID;
#define SDL_RenderFill(X) (X) ? SDL_RenderFillRect(X) : SDL_RenderClear()
#define SDL_KillThread(X)

/* The timeslice and timer resolution are no longer relevant */
#define SDL_TIMESLICE 10
#define TIMER_RESOLUTION 10

typedef Uint32 (SDLCALL * SDL_OldTimerCallback) (Uint32 interval);
extern DECLSPEC int SDLCALL SDL_SetTimer(Uint32 interval, SDL_OldTimerCallback callback);

extern DECLSPEC int SDLCALL SDL_putenv(const char *variable);

/*@}*//*Compatibility*/
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86 changes: 16 additions & 70 deletions include/SDL_timer.h
Expand Up @@ -41,104 +41,50 @@ extern "C" {
#endif

/**
* This is the OS scheduler timeslice, in milliseconds.
*/
#define SDL_TIMESLICE 10

/**
* This is the maximum resolution of the SDL timer on all platforms.
*/
#define TIMER_RESOLUTION 10 /**< Experimentally determined */

/**
* Get the number of milliseconds since the SDL library initialization.
* \brief Get the number of milliseconds since the SDL library initialization.
*
* Note that this value wraps if the program runs for more than ~49 days.
* \note This value wraps if the program runs for more than ~49 days.
*/
extern DECLSPEC Uint32 SDLCALL SDL_GetTicks(void);

/**
* Wait a specified number of milliseconds before returning.
* \brief Wait a specified number of milliseconds before returning.
*/
extern DECLSPEC void SDLCALL SDL_Delay(Uint32 ms);

/**
* Function prototype for the timer callback function.
*/
typedef Uint32(SDLCALL * SDL_TimerCallback) (Uint32 interval);

/**
* Set a callback to run after the specified number of milliseconds has
* elapsed. The callback function is passed the current timer interval
* and returns the next timer interval. If the returned value is the
* same as the one passed in, the periodic alarm continues, otherwise a
* new alarm is scheduled. If the callback returns 0, the periodic alarm
* is cancelled.
*
* To cancel a currently running timer, call
* \code SDL_SetTimer(0, NULL); \endcode
*
* The timer callback function may run in a different thread than your
* main code, and so shouldn't call any functions from within itself.
*
* The maximum resolution of this timer is 10 ms, which means that if
* you request a 16 ms timer, your callback will run approximately 20 ms
* later on an unloaded system. If you wanted to set a flag signaling
* a frame update at 30 frames per second (every 33 ms), you might set a
* timer for 30 ms:
* \code
* SDL_SetTimer((33/10)*10, flag_update);
* \endcode
*
* If you use this function, you need to pass ::SDL_INIT_TIMER to SDL_Init().
*
* Under UNIX, you should not use raise or use SIGALRM and this function
* in the same program, as it is implemented using setitimer(). You also
* should not use this function in multi-threaded applications as signals
* to multi-threaded apps have undefined behavior in some implementations.
*
* \return 0 if successful, or -1 if there was an error.
*/
extern DECLSPEC int SDLCALL SDL_SetTimer(Uint32 interval,
SDL_TimerCallback callback);

/**
* \name Peter timers
* New timer API, supports multiple timers
* Written by Stephane Peter <megastep@lokigames.com>
*/
/*@{*/

/**
* Function prototype for the new timer callback function.
*
* The callback function is passed the current timer interval and returns
* the next timer interval. If the returned value is the same as the one
* passed in, the periodic alarm continues, otherwise a new alarm is
* scheduled. If the callback returns 0, the periodic alarm is cancelled.
*/
typedef Uint32(SDLCALL * SDL_NewTimerCallback) (Uint32 interval, void *param);
typedef Uint32 (SDLCALL * SDL_TimerCallback) (Uint32 interval, void *param);

/**
* Definition of the timer ID type.
* Definition of the timer ID type.
*/
typedef struct _SDL_TimerID *SDL_TimerID;
typedef int SDL_TimerID;

/**
* Add a new timer to the pool of timers already running.
* \return A timer ID, or NULL when an error occurs.
* \brief Add a new timer to the pool of timers already running.
*
* \return A timer ID, or NULL when an error occurs.
*/
extern DECLSPEC SDL_TimerID SDLCALL SDL_AddTimer(Uint32 interval,
SDL_NewTimerCallback
callback, void *param);
SDL_TimerCallback callback,
void *param);

/**
* Remove one of the multiple timers knowing its ID.
* \return A boolean value indicating success or failure.
* \brief Remove a timer knowing its ID.
*
* \return A boolean value indicating success or failure.
*
* \warning It is not safe to remove a timer multiple times.
*/
extern DECLSPEC SDL_bool SDLCALL SDL_RemoveTimer(SDL_TimerID t);

/*@}*//*Peter timers*/

/* Ends C function definitions when using C++ */
#ifdef __cplusplus
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25 changes: 25 additions & 0 deletions src/SDL_compat.c
Expand Up @@ -1760,6 +1760,31 @@ SDL_EnableUNICODE(int enable)
return previous;
}

static Uint32
SDL_SetTimerCallback(Uint32 interval, void* param)
{
return ((SDL_OldTimerCallback)param)(interval);
}

int
SDL_SetTimer(Uint32 interval, SDL_OldTimerCallback callback)
{
static SDL_TimerID compat_timer;

if (compat_timer) {
SDL_RemoveTimer(compat_timer);
compat_timer = 0;
}

if (interval && callback) {
compat_timer = SDL_AddTimer(interval, SDL_SetTimerCallback, callback);
if (!compat_timer) {
return -1;
}
}
return 0;
}

int
SDL_putenv(const char *_var)
{
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6 changes: 0 additions & 6 deletions src/events/SDL_events.c
Expand Up @@ -123,9 +123,6 @@ SDL_GobbleEvents(void *unused)

/* Give up the CPU for the rest of our timeslice */
SDL_EventLock.safe = 1;
if (SDL_timer_running) {
SDL_ThreadedTimerCheck();
}
SDL_Delay(1);

/* Check for event locking.
Expand All @@ -140,7 +137,6 @@ SDL_GobbleEvents(void *unused)
SDL_EventLock.safe = 0;
SDL_mutexV(SDL_EventLock.lock);
}
SDL_SetTimerThreaded(0);
event_thread = 0;
return (0);
}
Expand Down Expand Up @@ -168,8 +164,6 @@ SDL_StartEventThread(Uint32 flags)
}
SDL_EventLock.safe = 0;

/* The event thread will handle timers too */
SDL_SetTimerThreaded(2);
#if (defined(__WIN32__) && !defined(_WIN32_WCE)) && !defined(HAVE_LIBC)
#undef SDL_CreateThread
SDL_EventThread =
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42 changes: 0 additions & 42 deletions src/timer/SDL_systimer.h

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