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libobs: Fix deferred update sometimes using stale data 

Currently we use a bool flag to signal the video thread that it should
call obs_source_deferred_update. This does not work correctly when the
update callback is slow and the update is triggered faster than the
callback can complete.

For example:
* the settings are set to state A
* defer_update is set
* obs_source_deferred_update is called and enters into the callback
* the callback starts making use of the settings in state A
* the settings are set to state B
* defer_update stays set
* the callback finishes
* defer_update is set to false

Now defer_update is false but the callback has only observed settings in
state A but not B.

This commit fixes this bug by keeping an update counter. If the counter
has changed while we were in the callback we know that we need to update
again.

The counter is atomic. The current version uses a plain bool which is a
data race as the value is written and read in parallel.
master
Valentin 2020-08-03 21:08:02 +02:00
parent 478f1de846
commit 4508cb03b5
2 changed files with 8 additions and 6 deletions
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2
libobs/obs-internal.h
View File

@ -599,7 +599,7 @@ struct obs_source {
bool owns_info_id;
/* signals to call the source update in the video thread */
bool defer_update;
long defer_update_count;
/* ensures show/hide are only called once */
volatile long show_refs;

12
libobs/obs-source.c
View File

@ -860,11 +860,13 @@ uint32_t obs_get_source_output_flags(const char *id)
static void obs_source_deferred_update(obs_source_t *source)
{
if (source->context.data && source->info.update)
if (source->context.data && source->info.update) {
long count = os_atomic_load_long(&source->defer_update_count);
source->info.update(source->context.data,
source->context.settings);
source->defer_update = false;
os_atomic_compare_swap_long(&source->defer_update_count, count,
0);
}
}
void obs_source_update(obs_source_t *source, obs_data_t *settings)
@ -876,7 +878,7 @@ void obs_source_update(obs_source_t *source, obs_data_t *settings)
obs_data_apply(source->context.settings, settings);
if (source->info.output_flags & OBS_SOURCE_VIDEO) {
source->defer_update = true;
os_atomic_inc_long(&source->defer_update_count);
} else if (source->context.data && source->info.update) {
source->info.update(source->context.data,
source->context.settings);
@ -1101,7 +1103,7 @@ void obs_source_video_tick(obs_source_t *source, float seconds)
if ((source->info.output_flags & OBS_SOURCE_ASYNC) != 0)
async_tick(source);
if (source->defer_update)
if (os_atomic_load_long(&source->defer_update_count) > 0)
obs_source_deferred_update(source);
/* reset the filter render texture information once every frame */