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Modifies WaitEvent and WaitEventTimeout to actually wait instead of polling

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When possible use native os functions to make a blocking call waiting for
an incoming event. Previous behavior was to continuously poll the event
queue with a small delay between each poll.

The blocking call uses a new optional video driver event,
WaitEventTimeout, if available. It is called only if an window
already shown is available. If present the window is designated
using the variable wakeup_window to receive a wakeup event if
needed.

The WaitEventTimeout function accept a timeout parameter. If
positive the call will wait for an event or return if the timeout
expired without any event. If the timeout is zero it will
implement a polling behavior. If the timeout is negative the
function will block indefinetely waiting for an event.

To let the main thread sees events sent form a different thread
a "wake-up" signal is sent to the main thread if the main thread
is in a blocking state. The wake-up event is sent to the designated
wakeup_window if present.

The wake-up event is sent only if the PushEvent call is coming
from a different thread. Before sending the wake-up event
the ID of the thread making the blocking call is saved using the
variable blocking_thread_id and it is compared to the current
thread's id to decide if the wake-up event should be sent.

Two new optional video device methods are introduced:

WaitEventTimeout
SendWakeupEvent

in addition the mutex

wakeup_lock

which is defined and initialized but only for the drivers supporting the
methods above.

If the methods are not present the system behaves as previously
performing a periodic polling of the events queue.

The blocking call is disabled if a joystick or sensor is detected
and falls back to previous behavior.
This commit is contained in:
Francesco Abbate
2021-03-12 21:58:20 +01:00
committed by Sam Lantinga
parent 40e5ce7fe5
commit 0dd7024d55
16 changed files with 716 additions and 132 deletions
Download Patch File Download Diff File Expand all files Collapse all files

106
src/events/SDL_events.c
View File

@@ -759,6 +759,80 @@ SDL_PollEvent(SDL_Event * event)
return SDL_WaitEventTimeout(event, 0);
}
static int
SDL_WaitEventTimeout_Device(_THIS, SDL_Window *wakeup_window, SDL_Event * event, int timeout)
{
/* Release any keys held down from last frame */
SDL_ReleaseAutoReleaseKeys();
for (;;) {
if (!_this->wakeup_lock || SDL_LockMutex(_this->wakeup_lock) == 0) {
int status = SDL_PeepEvents(event, 1, SDL_GETEVENT, SDL_FIRSTEVENT, SDL_LASTEVENT);
/* If status == 0 we are going to block so wakeup will be needed. */
if (status == 0) {
_this->wakeup_window = wakeup_window;
_this->blocking_thread_id = SDL_ThreadID();
} else {
_this->wakeup_window = NULL;
_this->blocking_thread_id = 0;
}
if (_this->wakeup_lock) {
SDL_UnlockMutex(_this->wakeup_lock);
}
if (status < 0) {
/* Got an error: return */
break;
}
if (status > 0) {
/* There is an event, we can return. */
SDL_SendPendingSignalEvents(); /* in case we had a signal handler fire, etc. */
return 1;
}
/* No events found in the queue, call WaitEventTimeout to wait for an event. */
status = _this->WaitEventTimeout(_this, timeout);
/* Set wakeup_window to NULL without holding the lock. */
_this->wakeup_window = NULL;
if (status <= 0) {
/* There is either an error or the timeout is elapsed: return */
return 0;
}
/* An event was found and pumped into the SDL events queue. Continue the loop
to let SDL_PeepEvents pick it up .*/
}
}
return 0;
}
static int
SDL_events_need_polling() {
SDL_bool need_polling = SDL_FALSE;
#if !SDL_JOYSTICK_DISABLED
need_polling = \
(!SDL_disabled_events[SDL_JOYAXISMOTION >> 8] || SDL_JoystickEventState(SDL_QUERY)) \
&& (SDL_NumJoysticks() > 0);
#endif
#if !SDL_SENSOR_DISABLED
need_polling = need_polling || (!SDL_disabled_events[SDL_SENSORUPDATE >> 8] && \
(SDL_NumSensors() > 0));
#endif
return need_polling;
}
static SDL_Window *
SDL_find_active_window(SDL_VideoDevice * _this)
{
SDL_Window *window;
for (window = _this->windows; window; window = window->next) {
if (!window->is_destroying) {
return window;
}
}
return NULL;
}
int
SDL_WaitEvent(SDL_Event * event)
{
@@ -768,11 +842,24 @@ SDL_WaitEvent(SDL_Event * event)
int
SDL_WaitEventTimeout(SDL_Event * event, int timeout)
{
SDL_VideoDevice *_this = SDL_GetVideoDevice();
SDL_bool need_polling = SDL_events_need_polling();
SDL_Window *wakeup_window = NULL;
Uint32 expiration = 0;
if (timeout > 0)
expiration = SDL_GetTicks() + timeout;
if (!need_polling && _this) {
/* Look if a shown window is available to send the wakeup event. */
wakeup_window = SDL_find_active_window(_this);
need_polling = (wakeup_window == NULL);
}
if (!need_polling && _this && _this->WaitEventTimeout && _this->SendWakeupEvent) {
return SDL_WaitEventTimeout_Device(_this, wakeup_window, event, timeout);
}
for (;;) {
SDL_PumpEvents();
switch (SDL_PeepEvents(event, 1, SDL_GETEVENT, SDL_FIRSTEVENT, SDL_LASTEVENT)) {
@@ -796,6 +883,24 @@ SDL_WaitEventTimeout(SDL_Event * event, int timeout)
}
}
static int
SDL_SendWakeupEvent()
{
SDL_VideoDevice *_this = SDL_GetVideoDevice();
if (!_this || !_this->SendWakeupEvent) {
return 0;
}
if (!_this->wakeup_lock || SDL_LockMutex(_this->wakeup_lock) == 0) {
if (_this->wakeup_window && _this->blocking_thread_id != 0 && _this->blocking_thread_id != SDL_ThreadID()) {
_this->SendWakeupEvent(_this, _this->wakeup_window);
}
if (_this->wakeup_lock) {
SDL_UnlockMutex(_this->wakeup_lock);
}
}
return 0;
}
int
SDL_PushEvent(SDL_Event * event)
{
@@ -845,6 +950,7 @@ SDL_PushEvent(SDL_Event * event)
return -1;
}
SDL_SendWakeupEvent();
SDL_GestureProcessEvent(event);
return 1;