Multithread program screen freeze

SDL Development
#1

Hi, all

I used SDL in my v4l program with SDL_mixer, SDL_timer, SDL_thread. I create a SDL thread to grab video stream from bt878 by v4l2 and bitblt, update the video to screen, a timer loop bitblt and update to screen 10 times a second too. sometime the screen froze but the mp3 music still play. The program cannot quit. Can somebody help me? thanks

my code:

timer loop:-------------------------------------------------
static Uint32 timer_loop(Uint32 interval)
{
SDL_BlitSurface(t_surface, 0, core_screen, &t_rect);
SDL_UpdateRects(core_screen, 1, &t_rect);
return 100;
}

thread loop:

static int vidcap_thread(void* data)
{
int i;
struct v4l2_buffer buf;
enum v4l2_buf_type type;

while(1) {
	memset(&buf, 0 ,sizeof(buf));
	buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	buf.memory = V4L2_MEMORY_MMAP;
	buf.field =	V4L2_FIELD_ANY;

	if (ioctl(cap_fd, VIDIOC_DQBUF, &buf)==-1) {
		if (errno==EAGAIN) continue;
		break;
	}

	if (buf.index<MAX_BUFF) {
		SDL_BlitSurface(cap_surface[buf.index] , &cap_rect, core_screen, &screen_rect);
		SDL_UpdateRects(core_screen, 1, &screen_rect);
	}

	if (ioctl (cap_fd, VIDIOC_QBUF, &buf)==-1) break;
}//end while

//fail
type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
ioctl (cap_fd, VIDIOC_STREAMOFF, &type);

for (i=0;i<MAX_BUFF;i++) {
	SDL_FreeSurface(cap_surface[i]);
	munmap (cap_buff[i].addr, cap_buff[i].size);
}

cap_living = 0;

return 0;

}

sorry for my pool english

#2

SDL documents that its video functions are not (in general) thread
safe, and on some platforms must be called from the main thread. You
might want to look into a producer/consumer model using the SDL_Event
system to facilitate inter-thread communications.On Wed, Dec 23, 2009 at 3:20 PM, antzhi wrote:

Hi, all

I used SDL in my v4l program with SDL_mixer, SDL_timer, SDL_thread. I create
a SDL thread to grab video stream from bt878 by v4l2 and bitblt, update the
video to screen, a timer loop bitblt and update to screen 10 times a second
too. sometime the screen froze but the mp3 music still play. The program
cannot quit. Can somebody help me? thanks

#3

Thank you, I add a mutex to fix this problem, all is ok

Brian Barrett wrote:> SDL documents that its video functions are not (in general) thread

safe, and on some platforms must be called from the main thread. You
might want to look into a producer/consumer model using the SDL_Event
system to facilitate inter-thread communications.

On Wed, Dec 23, 2009 at 3:20 PM, antzhi <@antzhi> wrote:

Hi, all

I used SDL in my v4l program with SDL_mixer, SDL_timer, SDL_thread. I create
a SDL thread to grab video stream from bt878 by v4l2 and bitblt, update the
video to screen, a timer loop bitblt and update to screen 10 times a second
too. sometime the screen froze but the mp3 music still play. The program
cannot quit. Can somebody help me? thanks

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#4

Strictly speaking, SDL does not support blitting to the screen from
different threads, regardless of the presence of mutexes. If you want your
application to be portable, you will need a more robust solution.On Wed, Dec 23, 2009 at 8:24 PM, antzhi wrote:

Thank you, I add a mutex to fix this problem, all is ok

#5

yes, maybe i need a “blit” thread to do all blitting

Brian Barrett wrote:> Strictly speaking, SDL does not support blitting to the screen from different threads, regardless of the presence of mutexes. If you want your application to be portable, you will need a more robust solution.

On Wed, Dec 23, 2009 at 8:24 PM, antzhi <@antzhi (@antzhi)> wrote:

  Thank you, I add a mutex to fix this problem, all is ok