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wayland: Use multi-thread event reading APIs 

Wayland provides the prepare_read()/read_events() family of APIs for
reading from the display fd in a deadlock-free manner across multiple
threads in a multi-threaded application. Let's use those instead of
trying to roll our own solution using a mutex.

This fixes an issue where a call to SDL_GL_SwapWindow() doesn't swap
buffers if it happens to collide with SDL_PumpEvents() in the main
thread. It also allows coexistence with other code or toolkits in
our process that may want read and dispatch events themselves.
This commit is contained in:
Cameron Gutman 2021-10-23 15:43:04 -05:00 committed by Ethan Lee
parent 4960cc3dcb
commit 408a93a1ec
5 changed files with 29 additions and 30 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

22
src/video/wayland/SDL_waylandevents.c
View File

@ -231,20 +231,18 @@ Wayland_PumpEvents(_THIS)
keyboard_repeat_handle(&input->keyboard_repeat, now);
}
/* If we're trying to dispatch the display in another thread,
* we could trigger a race condition and end up blocking
* in wl_display_dispatch() */
if (SDL_TryLockMutex(d->display_dispatch_lock) != 0) {
return;
/* wl_display_prepare_read() will return -1 if the default queue is not empty.
* If the default queue is empty, it will prepare us for our SDL_IOReady() call. */
if (WAYLAND_wl_display_prepare_read(d->display) == 0) {
if (SDL_IOReady(WAYLAND_wl_display_get_fd(d->display), SDL_FALSE, 0) > 0) {
WAYLAND_wl_display_read_events(d->display);
} else {
WAYLAND_wl_display_cancel_read(d->display);
}
}
if (SDL_IOReady(WAYLAND_wl_display_get_fd(d->display), SDL_FALSE, 0)) {
err = WAYLAND_wl_display_dispatch(d->display);
} else {
err = WAYLAND_wl_display_dispatch_pending(d->display);
}
SDL_UnlockMutex(d->display_dispatch_lock);
/* Dispatch any pre-existing pending events or new events we may have read */
err = WAYLAND_wl_display_dispatch_pending(d->display);
if (err == -1 && !d->display_disconnected) {
/* Something has failed with the Wayland connection -- for example,

29
src/video/wayland/SDL_waylandopengles.c
View File

@ -136,33 +136,34 @@ Wayland_GLES_SwapWindow(_THIS, SDL_Window *window)
while (SDL_AtomicGet(&data->swap_interval_ready) == 0) {
Uint32 now;
/* !!! FIXME: this is just the crucial piece of Wayland_PumpEvents */
WAYLAND_wl_display_flush(display);
if (WAYLAND_wl_display_dispatch_queue_pending(display, data->frame_event_queue) > 0) {
/* We dispatched some pending events. Check if the frame callback happened. */
/* wl_display_prepare_read_queue() will return -1 if the event queue is not empty.
* If the event queue is empty, it will prepare us for our SDL_IOReady() call. */
if (WAYLAND_wl_display_prepare_read_queue(display, data->frame_event_queue) != 0) {
/* We have some pending events. Check if the frame callback happened. */
WAYLAND_wl_display_dispatch_queue_pending(display, data->frame_event_queue);
continue;
}
/* Beyond this point, we must either call wl_display_cancel_read() or wl_display_read_events() */
now = SDL_GetTicks();
if (SDL_TICKS_PASSED(now, max_wait)) {
/* Timeout expired */
/* Timeout expired. Cancel the read. */
WAYLAND_wl_display_cancel_read(display);
break;
}
/* Make sure we're not competing with SDL_PumpEvents() for any new
* events, or one of us may end up blocking in wl_display_dispatch */
if (SDL_TryLockMutex(videodata->display_dispatch_lock) != 0) {
continue;
}
if (SDL_IOReady(WAYLAND_wl_display_get_fd(display), SDL_FALSE, max_wait - now) <= 0) {
/* Error or timeout expired without any events for us */
SDL_UnlockMutex(videodata->display_dispatch_lock);
/* Error or timeout expired without any events for us. Cancel the read. */
WAYLAND_wl_display_cancel_read(display);
break;
}
WAYLAND_wl_display_dispatch_queue(display, data->frame_event_queue);
SDL_UnlockMutex(videodata->display_dispatch_lock);
/* We have events. Read and dispatch them. */
WAYLAND_wl_display_read_events(display);
WAYLAND_wl_display_dispatch_queue_pending(display, data->frame_event_queue);
}
SDL_AtomicSet(&data->swap_interval_ready, 0);
}

4
src/video/wayland/SDL_waylandsym.h
View File

@ -56,6 +56,10 @@ SDL_WAYLAND_SYM(int, wl_display_dispatch, (struct wl_display *))
SDL_WAYLAND_SYM(int, wl_display_dispatch_queue, (struct wl_display *, struct wl_event_queue *))
SDL_WAYLAND_SYM(int, wl_display_dispatch_queue_pending, (struct wl_display *, struct wl_event_queue *))
SDL_WAYLAND_SYM(int, wl_display_dispatch_pending, (struct wl_display *))
SDL_WAYLAND_SYM(int, wl_display_prepare_read, (struct wl_display *))
SDL_WAYLAND_SYM(int, wl_display_prepare_read_queue, (struct wl_display *, struct wl_event_queue *))
SDL_WAYLAND_SYM(int, wl_display_read_events, (struct wl_display *))
SDL_WAYLAND_SYM(void, wl_display_cancel_read, (struct wl_display *))
SDL_WAYLAND_SYM(int, wl_display_get_error, (struct wl_display *))
SDL_WAYLAND_SYM(int, wl_display_flush, (struct wl_display *))
SDL_WAYLAND_SYM(int, wl_display_roundtrip, (struct wl_display *))

3
src/video/wayland/SDL_waylandvideo.c
View File

@ -169,7 +169,6 @@ Wayland_DeleteDevice(SDL_VideoDevice *device)
WAYLAND_wl_display_flush(data->display);
WAYLAND_wl_display_disconnect(data->display);
}
SDL_DestroyMutex(data->display_dispatch_lock);
SDL_free(data);
SDL_free(device);
SDL_WAYLAND_UnloadSymbols();
@ -202,8 +201,6 @@ Wayland_CreateDevice(int devindex)
data->display = display;
data->display_dispatch_lock = SDL_CreateMutex();
/* Initialize all variables that we clean on shutdown */
device = SDL_calloc(1, sizeof(SDL_VideoDevice));
if (!device) {

1
src/video/wayland/SDL_waylandvideo.h
View File

@ -86,7 +86,6 @@ typedef struct {
char *classname;
int relative_mouse_mode;
SDL_mutex *display_dispatch_lock;
} SDL_VideoData;
typedef struct {