[PATCH/RFC v2 0/2] libv4l2: fix deadlock when DQBUF in block mode

[PATCH/RFC v2 0/2] libv4l2: fix deadlock when DQBUF in block mode

[Thiago Santos]

Hello,

thanks for the reviews and comments. I updated the example as suggested by
Mauro and reimplemented the deadlock fix as suggested by Hans. Here is the
second version of those patches.

Thiago Santos (2):
  v4l2grab: Add threaded producer/consumer option
  libv4l2: release the lock before doing a DQBUF

 contrib/test/Makefile.am   |   2 +-
 contrib/test/v4l2grab.c    | 261 +++++++++++++++++++++++++++++++++++++--------
 lib/libv4l2/libv4l2-priv.h |   1 +
 lib/libv4l2/libv4l2.c      |  13 ++-
 4 files changed, 232 insertions(+), 45 deletions(-)

-- 
2.0.0

[PATCH/RFC v2 1/2] v4l2grab: Add threaded producer/consumer option

[Thiago Santos]

Adds options to allow the buffer dqbuf to happen on one thread while
the qbuf happens on another. This is useful to test concurrency access to
the v4l2 features. To enable this, 3 new options were added:

t: enable threaded mode (off by default and will use the loop)
b: enable blocking io mode (off by default
s: how much the consumer thread will sleep after reading a buffer, this is to
   simulate the time that it takes to process a buffer in a real application
   (in ms)

For example, you can simulate an application that takes 1s to process a buffer
with:

v4l2grab -t -b -s 1000

Signed-off-by: Thiago Santos <ts.santos@sisa.samsung.com>
---
 contrib/test/Makefile.am |   2 +-
 contrib/test/v4l2grab.c  | 261 +++++++++++++++++++++++++++++++++++++++--------
 2 files changed, 219 insertions(+), 44 deletions(-)

diff --git a/contrib/test/Makefile.am b/contrib/test/Makefile.am
index 80c7665..c2e3860 100644
--- a/contrib/test/Makefile.am
+++ b/contrib/test/Makefile.am
@@ -25,7 +25,7 @@ pixfmt_test_CFLAGS = $(X11_CFLAGS)
 pixfmt_test_LDFLAGS = $(X11_LIBS)
 
 v4l2grab_SOURCES = v4l2grab.c
-v4l2grab_LDADD = ../../lib/libv4l2/libv4l2.la ../../lib/libv4lconvert/libv4lconvert.la
+v4l2grab_LDADD = ../../lib/libv4l2/libv4l2.la ../../lib/libv4lconvert/libv4lconvert.la -lpthread
 
 v4l2gl_SOURCES = v4l2gl.c
 v4l2gl_LDFLAGS = $(X11_LIBS) $(GL_LIBS) $(GLU_LIBS)
diff --git a/contrib/test/v4l2grab.c b/contrib/test/v4l2grab.c
index 674cbe7..3e1be3d 100644
--- a/contrib/test/v4l2grab.c
+++ b/contrib/test/v4l2grab.c
@@ -24,8 +24,10 @@
 #include <linux/videodev2.h>
 #include "../../lib/include/libv4l2.h"
 #include <argp.h>
+#include <pthread.h>
 
-#define CLEAR(x) memset(&(x), 0, sizeof(x))
+#define CLEAR_P(x,s) memset((x), 0, s)
+#define CLEAR(x) CLEAR_P(&(x), sizeof(x))
 
 struct buffer {
 	void   *start;
@@ -46,22 +48,206 @@ static void xioctl(int fh, unsigned long int request, void *arg)
 	}
 }
 
+/* Used by the multi thread capture version */
+struct buffer_queue {
+	struct v4l2_buffer *buffers;
+	int buffers_size;
+
+	int read_pos;
+	int write_pos;
+	int n_frames;
+
+	int fd;
+
+	pthread_mutex_t mutex;
+	pthread_cond_t buffer_cond;
+};
+
+/* Gets a buffer and puts it in the buffers list at write position, then
+ * notifies the consumer that a new buffer is ready to be used */
+static void *produce_buffer (void * p)
+{
+	struct buffer_queue 		*bq;
+	fd_set				fds;
+	struct timeval			tv;
+	int				i;
+	struct v4l2_buffer		*buf;
+	int				r;
+
+	bq = p;
+
+	for (i = 0; i < bq->n_frames; i++) {
+		printf ("Prod: %d\n", i);
+		buf = &bq->buffers[bq->write_pos % bq->buffers_size];
+		do {
+			FD_ZERO(&fds);
+			FD_SET(bq->fd, &fds);
+
+			/* Timeout. */
+			tv.tv_sec = 2;
+			tv.tv_usec = 0;
+
+			r = select(bq->fd + 1, &fds, NULL, NULL, &tv);
+		} while ((r == -1 && (errno == EINTR)));
+		if (r == -1) {
+			perror("select");
+			pthread_exit (NULL);
+			return NULL;
+		}
+
+		CLEAR_P(buf, sizeof(struct v4l2_buffer));
+		buf->type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+		buf->memory = V4L2_MEMORY_MMAP;
+		xioctl(bq->fd, VIDIOC_DQBUF, buf);
+
+		pthread_mutex_lock (&bq->mutex);
+		bq->write_pos++;
+		printf ("Prod: %d (done)\n", i);
+		pthread_cond_signal (&bq->buffer_cond);
+		pthread_mutex_unlock (&bq->mutex);
+
+	}
+
+	pthread_exit (NULL);
+}
+
+/* will create a separate thread that will produce the buffers and put
+ * into a circular array while this same thread will get the buffers from
+ * this array and 'render' them */
+static int capture_threads (int fd, struct buffer *buffers, int bufpool_size,
+			struct v4l2_format fmt, int n_frames,
+			char *out_dir, int sleep_ms)
+{
+	struct v4l2_buffer		buf;
+	unsigned int			i;
+	struct buffer_queue		buf_queue;
+	pthread_t			producer;
+	char				out_name[25 + strlen(out_dir)];
+	FILE				*fout;
+	struct timespec			sleeptime;
+
+	if (sleep_ms) {
+		sleeptime.tv_sec = sleep_ms / 1000;
+		sleeptime.tv_nsec = (sleep_ms % 1000) * 1000000;
+	}
+
+	buf_queue.buffers_size = bufpool_size * 2;
+	buf_queue.buffers = calloc(buf_queue.buffers_size,
+				   sizeof(struct v4l2_buffer));
+	buf_queue.fd = fd;
+	buf_queue.read_pos = 0;
+	buf_queue.write_pos = 0;
+	buf_queue.n_frames = n_frames;
+	pthread_mutex_init (&buf_queue.mutex, NULL);
+	pthread_cond_init (&buf_queue.buffer_cond, NULL);
+
+	pthread_create (&producer, NULL, produce_buffer, &buf_queue);
+
+	for (i = 0; i < n_frames; i++) {
+		printf ("Read: %d\n", i);
+
+		/* wait for a buffer to be available in the queue */
+		pthread_mutex_lock (&buf_queue.mutex);
+		while (buf_queue.read_pos == buf_queue.write_pos) {
+			pthread_cond_wait (&buf_queue.buffer_cond,
+					   &buf_queue.mutex);
+		}
+		pthread_mutex_unlock (&buf_queue.mutex);
+
+		if (sleep_ms)
+			nanosleep (&sleeptime, NULL);
+
+		sprintf(out_name, "%s/out%03d.ppm", out_dir, i);
+		fout = fopen(out_name, "w");
+		if (!fout) {
+			perror("Cannot open image");
+			exit(EXIT_FAILURE);
+		}
+		fprintf(fout, "P6\n%d %d 255\n",
+			fmt.fmt.pix.width, fmt.fmt.pix.height);
+		buf = buf_queue.buffers[buf_queue.read_pos %
+					buf_queue.buffers_size];
+		fwrite(buffers[buf.index].start, buf.bytesused, 1, fout);
+		fclose(fout);
+
+		xioctl(fd, VIDIOC_QBUF, &buf);
+
+		pthread_mutex_lock (&buf_queue.mutex);
+		buf_queue.read_pos++;
+		printf ("Read: %d (done)\n", i);
+		pthread_cond_signal (&buf_queue.buffer_cond);
+		pthread_mutex_unlock (&buf_queue.mutex);
+	}
+
+	pthread_mutex_destroy (&buf_queue.mutex);
+	pthread_cond_destroy (&buf_queue.buffer_cond);
+	free (buf_queue.buffers);
+	return 0;
+}
+
+static int capture_loop (int fd, struct buffer *buffers, struct v4l2_format fmt,
+			int n_frames, char *out_dir)
+{
+	struct v4l2_buffer		buf;
+	unsigned int			i;
+	struct timeval			tv;
+	int				r;
+	fd_set				fds;
+	FILE				*fout;
+	char				out_name[25 + strlen(out_dir)];
+
+	for (i = 0; i < n_frames; i++) {
+		do {
+			FD_ZERO(&fds);
+			FD_SET(fd, &fds);
+
+			/* Timeout. */
+			tv.tv_sec = 2;
+			tv.tv_usec = 0;
+
+			r = select(fd + 1, &fds, NULL, NULL, &tv);
+		} while ((r == -1 && (errno == EINTR)));
+		if (r == -1) {
+			perror("select");
+			return errno;
+		}
+
+		CLEAR(buf);
+		buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
+		buf.memory = V4L2_MEMORY_MMAP;
+		xioctl(fd, VIDIOC_DQBUF, &buf);
+
+		sprintf(out_name, "%s/out%03d.ppm", out_dir, i);
+		fout = fopen(out_name, "w");
+		if (!fout) {
+			perror("Cannot open image");
+			exit(EXIT_FAILURE);
+		}
+		fprintf(fout, "P6\n%d %d 255\n",
+			fmt.fmt.pix.width, fmt.fmt.pix.height);
+		fwrite(buffers[buf.index].start, buf.bytesused, 1, fout);
+		fclose(fout);
+
+		xioctl(fd, VIDIOC_QBUF, &buf);
+	}
+	return 0;
+}
+
 static int capture(char *dev_name, int x_res, int y_res, int n_frames,
-		   char *out_dir)
+		   char *out_dir, int block, int threads, int sleep_ms)
 {
 	struct v4l2_format		fmt;
 	struct v4l2_buffer		buf;
 	struct v4l2_requestbuffers	req;
 	enum v4l2_buf_type		type;
-	fd_set				fds;
-	struct timeval			tv;
-	int				r, fd = -1;
+	int				fd = -1;
 	unsigned int			i, n_buffers;
-	char				out_name[25 + strlen(out_dir)];
-	FILE				*fout;
 	struct buffer			*buffers;
 
-	fd = v4l2_open(dev_name, O_RDWR | O_NONBLOCK, 0);
+	if (block)
+		fd = v4l2_open(dev_name, O_RDWR, 0);
+	else
+		fd = v4l2_open(dev_name, O_RDWR | O_NONBLOCK, 0);
 	if (fd < 0) {
 		perror("Cannot open device");
 		exit(EXIT_FAILURE);
@@ -119,40 +305,11 @@ static int capture(char *dev_name, int x_res, int y_res, int n_frames,
 	type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
 
 	xioctl(fd, VIDIOC_STREAMON, &type);
-	for (i = 0; i < n_frames; i++) {
-		do {
-			FD_ZERO(&fds);
-			FD_SET(fd, &fds);
-
-			/* Timeout. */
-			tv.tv_sec = 2;
-			tv.tv_usec = 0;
-
-			r = select(fd + 1, &fds, NULL, NULL, &tv);
-		} while ((r == -1 && (errno == EINTR)));
-		if (r == -1) {
-			perror("select");
-			return errno;
-		}
-
-		CLEAR(buf);
-		buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
-		buf.memory = V4L2_MEMORY_MMAP;
-		xioctl(fd, VIDIOC_DQBUF, &buf);
-
-		sprintf(out_name, "%s/out%03d.ppm", out_dir, i);
-		fout = fopen(out_name, "w");
-		if (!fout) {
-			perror("Cannot open image");
-			exit(EXIT_FAILURE);
-		}
-		fprintf(fout, "P6\n%d %d 255\n",
-			fmt.fmt.pix.width, fmt.fmt.pix.height);
-		fwrite(buffers[buf.index].start, buf.bytesused, 1, fout);
-		fclose(fout);
-
-		xioctl(fd, VIDIOC_QBUF, &buf);
-	}
+	if (threads)
+		capture_threads(fd, buffers, 2, fmt, n_frames, out_dir,
+				sleep_ms);
+	else
+		capture_loop(fd, buffers, fmt, n_frames, out_dir);
 
 	type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
 	xioctl(fd, VIDIOC_STREAMOFF, &type);
@@ -179,6 +336,9 @@ static const struct argp_option options[] = {
 	{"xres",	'x',	"XRES",		0,	"horizontal resolution", 0},
 	{"yres",	'y',	"YRES",		0,	"vertical resolution", 0},
 	{"n-frames",	'n',	"NFRAMES",	0,	"number of frames to capture", 0},
+	{"thread-enable", 't',	"THREADS",	0,	"if different threads should capture and save", 0},
+	{"blockmode-enable", 'b', "BLOCKMODE",	0,	"if blocking mode should be used", 0},
+	{"sleep-time",	's',	"SLEEP",	0,	"how long should the consumer thread sleep to simulate the processing of a buffer (in ms)"},
 	{ 0, 0, 0, 0, 0, 0 }
 };
 
@@ -188,6 +348,9 @@ static char	*out_dir = ".";
 static int	x_res = 640;
 static int	y_res = 480;
 static int	n_frames = 20;
+static int	threads = 0;
+static int	block = 0;
+static int	sleep_ms = 0;
 
 static error_t parse_opt(int k, char *arg, struct argp_state *state)
 {
@@ -215,6 +378,17 @@ static error_t parse_opt(int k, char *arg, struct argp_state *state)
 		if (val)
 			n_frames = val;
 		break;
+	case 't':
+		threads = 1;
+		break;
+	case 'b':
+		block = 1;
+		break;
+	case 's':
+		val = atoi(arg);
+		if (val)
+			sleep_ms = val;
+		break;
 	default:
 		return ARGP_ERR_UNKNOWN;
 	}
@@ -232,5 +406,6 @@ int main(int argc, char **argv)
 {
 	argp_parse(&argp, argc, argv, 0, 0, 0);
 
-	return capture(dev_name, x_res, y_res, n_frames, out_dir);
+	return capture(dev_name, x_res, y_res, n_frames, out_dir, block,
+		       threads, sleep_ms);
 }
-- 
2.0.0

[PATCH/RFC v2 2/2] libv4l2: release the lock before doing a DQBUF

[Thiago Santos]

In blocking mode, if there are no buffers available the DQBUF will block
waiting for a QBUF to be called but it will block holding the streaming
lock which will prevent any QBUF from happening, causing a deadlock.

Can be tested with: v4l2grab -t -b -s 2000

Signed-off-by: Thiago Santos <ts.santos@sisa.samsung.com>
---
 lib/libv4l2/libv4l2-priv.h |  1 +
 lib/libv4l2/libv4l2.c      | 13 ++++++++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/lib/libv4l2/libv4l2-priv.h b/lib/libv4l2/libv4l2-priv.h
index 585273c..ff4c8d2 100644
--- a/lib/libv4l2/libv4l2-priv.h
+++ b/lib/libv4l2/libv4l2-priv.h
@@ -92,6 +92,7 @@ struct v4l2_dev_info {
 	unsigned char *frame_pointers[V4L2_MAX_NO_FRAMES];
 	int frame_sizes[V4L2_MAX_NO_FRAMES];
 	int frame_queued; /* 1 status bit per frame */
+	int frame_info_generation;
 	/* mapping tracking of our fake (converting mmap) frame buffers */
 	unsigned char frame_map_count[V4L2_MAX_NO_FRAMES];
 	/* buffer when doing conversion and using read() for read() */
diff --git a/lib/libv4l2/libv4l2.c b/lib/libv4l2/libv4l2.c
index c4d69f7..1dcf34d 100644
--- a/lib/libv4l2/libv4l2.c
+++ b/lib/libv4l2/libv4l2.c
@@ -282,7 +282,7 @@ static int v4l2_dequeue_and_convert(int index, struct v4l2_buffer *buf,
 		unsigned char *dest, int dest_size)
 {
 	const int max_tries = V4L2_IGNORE_FIRST_FRAME_ERRORS + 1;
-	int result, tries = max_tries;
+	int result, tries = max_tries, frame_info_gen;
 
 	/* Make sure we have the real v4l2 buffers mapped */
 	result = v4l2_map_buffers(index);
@@ -290,9 +290,12 @@ static int v4l2_dequeue_and_convert(int index, struct v4l2_buffer *buf,
 		return result;
 
 	do {
+		frame_info_gen = devices[index].frame_info_generation;
+		pthread_mutex_unlock(&devices[index].stream_lock);
 		result = devices[index].dev_ops->ioctl(
 				devices[index].dev_ops_priv,
 				devices[index].fd, VIDIOC_DQBUF, buf);
+		pthread_mutex_lock(&devices[index].stream_lock);
 		if (result) {
 			if (errno != EAGAIN) {
 				int saved_err = errno;
@@ -305,6 +308,11 @@ static int v4l2_dequeue_and_convert(int index, struct v4l2_buffer *buf,
 
 		devices[index].frame_queued &= ~(1 << buf->index);
 
+		if (frame_info_gen != devices[index].frame_info_generation) {
+			errno = -EINVAL;
+			return -1;
+		}
+
 		result = v4lconvert_convert(devices[index].convert,
 				&devices[index].src_fmt, &devices[index].dest_fmt,
 				devices[index].frame_pointers[buf->index],
@@ -839,6 +847,7 @@ int v4l2_dup(int fd)
 
 static int v4l2_check_buffer_change_ok(int index)
 {
+	devices[index].frame_info_generation++;
 	v4l2_unmap_buffers(index);
 
 	/* Check if the app itself still is using the stream */
@@ -1294,9 +1303,11 @@ no_capture_request:
 		}
 
 		if (!v4l2_needs_conversion(index)) {
+			pthread_mutex_unlock(&devices[index].stream_lock);
 			result = devices[index].dev_ops->ioctl(
 					devices[index].dev_ops_priv,
 					fd, VIDIOC_DQBUF, buf);
+			pthread_mutex_lock(&devices[index].stream_lock);
 			if (result) {
 				saved_err = errno;
 				V4L2_PERROR("dequeuing buf");
-- 
2.0.0

Re: [PATCH/RFC v2 2/2] libv4l2: release the lock before doing a DQBUF

[Hans de Goede]

Hi,

On 06/09/2014 03:51 PM, Thiago Santos wrote:
> In blocking mode, if there are no buffers available the DQBUF will block
> waiting for a QBUF to be called but it will block holding the streaming
> lock which will prevent any QBUF from happening, causing a deadlock.
> 
> Can be tested with: v4l2grab -t -b -s 2000
> 
> Signed-off-by: Thiago Santos <ts.santos@sisa.samsung.com>

Looks good now:

Acked-by: Hans de Goede <hdegoede@redhat.com>

I'll leave reviewing the 1st patch to someone else. Gregor and/or
Mauro feel free to push this one.

Regards,

Hans

> ---
>  lib/libv4l2/libv4l2-priv.h |  1 +
>  lib/libv4l2/libv4l2.c      | 13 ++++++++++++-
>  2 files changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/libv4l2/libv4l2-priv.h b/lib/libv4l2/libv4l2-priv.h
> index 585273c..ff4c8d2 100644
> --- a/lib/libv4l2/libv4l2-priv.h
> +++ b/lib/libv4l2/libv4l2-priv.h
> @@ -92,6 +92,7 @@ struct v4l2_dev_info {
>  	unsigned char *frame_pointers[V4L2_MAX_NO_FRAMES];
>  	int frame_sizes[V4L2_MAX_NO_FRAMES];
>  	int frame_queued; /* 1 status bit per frame */
> +	int frame_info_generation;
>  	/* mapping tracking of our fake (converting mmap) frame buffers */
>  	unsigned char frame_map_count[V4L2_MAX_NO_FRAMES];
>  	/* buffer when doing conversion and using read() for read() */
> diff --git a/lib/libv4l2/libv4l2.c b/lib/libv4l2/libv4l2.c
> index c4d69f7..1dcf34d 100644
> --- a/lib/libv4l2/libv4l2.c
> +++ b/lib/libv4l2/libv4l2.c
> @@ -282,7 +282,7 @@ static int v4l2_dequeue_and_convert(int index, struct v4l2_buffer *buf,
>  		unsigned char *dest, int dest_size)
>  {
>  	const int max_tries = V4L2_IGNORE_FIRST_FRAME_ERRORS + 1;
> -	int result, tries = max_tries;
> +	int result, tries = max_tries, frame_info_gen;
>  
>  	/* Make sure we have the real v4l2 buffers mapped */
>  	result = v4l2_map_buffers(index);
> @@ -290,9 +290,12 @@ static int v4l2_dequeue_and_convert(int index, struct v4l2_buffer *buf,
>  		return result;
>  
>  	do {
> +		frame_info_gen = devices[index].frame_info_generation;
> +		pthread_mutex_unlock(&devices[index].stream_lock);
>  		result = devices[index].dev_ops->ioctl(
>  				devices[index].dev_ops_priv,
>  				devices[index].fd, VIDIOC_DQBUF, buf);
> +		pthread_mutex_lock(&devices[index].stream_lock);
>  		if (result) {
>  			if (errno != EAGAIN) {
>  				int saved_err = errno;
> @@ -305,6 +308,11 @@ static int v4l2_dequeue_and_convert(int index, struct v4l2_buffer *buf,
>  
>  		devices[index].frame_queued &= ~(1 << buf->index);
>  
> +		if (frame_info_gen != devices[index].frame_info_generation) {
> +			errno = -EINVAL;
> +			return -1;
> +		}
> +
>  		result = v4lconvert_convert(devices[index].convert,
>  				&devices[index].src_fmt, &devices[index].dest_fmt,
>  				devices[index].frame_pointers[buf->index],
> @@ -839,6 +847,7 @@ int v4l2_dup(int fd)
>  
>  static int v4l2_check_buffer_change_ok(int index)
>  {
> +	devices[index].frame_info_generation++;
>  	v4l2_unmap_buffers(index);
>  
>  	/* Check if the app itself still is using the stream */
> @@ -1294,9 +1303,11 @@ no_capture_request:
>  		}
>  
>  		if (!v4l2_needs_conversion(index)) {
> +			pthread_mutex_unlock(&devices[index].stream_lock);
>  			result = devices[index].dev_ops->ioctl(
>  					devices[index].dev_ops_priv,
>  					fd, VIDIOC_DQBUF, buf);
> +			pthread_mutex_lock(&devices[index].stream_lock);
>  			if (result) {
>  				saved_err = errno;
>  				V4L2_PERROR("dequeuing buf");
> 

Re: [PATCH/RFC v2 1/2] v4l2grab: Add threaded producer/consumer option

[Hans Verkuil]

On 06/09/2014 03:51 PM, Thiago Santos wrote:
> Adds options to allow the buffer dqbuf to happen on one thread while
> the qbuf happens on another. This is useful to test concurrency access to
> the v4l2 features. To enable this, 3 new options were added:
> 
> t: enable threaded mode (off by default and will use the loop)
> b: enable blocking io mode (off by default
> s: how much the consumer thread will sleep after reading a buffer, this is to
>    simulate the time that it takes to process a buffer in a real application
>    (in ms)
> 
> For example, you can simulate an application that takes 1s to process a buffer
> with:
> 
> v4l2grab -t -b -s 1000

Is there a reason why you want to use v4l2grab instead of v4l2-ctl? My guess is
that is was just easier to add it there. I'm not so keen about this, I'd much
rather see this being added to v4l2-ctl, ideally for both capture, output and
m2m devices.

I'll commit the second patch since HdG Acked it.

Regards,

	Hans

> 
> Signed-off-by: Thiago Santos <ts.santos@sisa.samsung.com>
> ---
>  contrib/test/Makefile.am |   2 +-
>  contrib/test/v4l2grab.c  | 261 +++++++++++++++++++++++++++++++++++++++--------
>  2 files changed, 219 insertions(+), 44 deletions(-)
> 
> diff --git a/contrib/test/Makefile.am b/contrib/test/Makefile.am
> index 80c7665..c2e3860 100644
> --- a/contrib/test/Makefile.am
> +++ b/contrib/test/Makefile.am
> @@ -25,7 +25,7 @@ pixfmt_test_CFLAGS = $(X11_CFLAGS)
>  pixfmt_test_LDFLAGS = $(X11_LIBS)
>  
>  v4l2grab_SOURCES = v4l2grab.c
> -v4l2grab_LDADD = ../../lib/libv4l2/libv4l2.la ../../lib/libv4lconvert/libv4lconvert.la
> +v4l2grab_LDADD = ../../lib/libv4l2/libv4l2.la ../../lib/libv4lconvert/libv4lconvert.la -lpthread
>  
>  v4l2gl_SOURCES = v4l2gl.c
>  v4l2gl_LDFLAGS = $(X11_LIBS) $(GL_LIBS) $(GLU_LIBS)
> diff --git a/contrib/test/v4l2grab.c b/contrib/test/v4l2grab.c
> index 674cbe7..3e1be3d 100644
> --- a/contrib/test/v4l2grab.c
> +++ b/contrib/test/v4l2grab.c
> @@ -24,8 +24,10 @@
>  #include <linux/videodev2.h>
>  #include "../../lib/include/libv4l2.h"
>  #include <argp.h>
> +#include <pthread.h>
>  
> -#define CLEAR(x) memset(&(x), 0, sizeof(x))
> +#define CLEAR_P(x,s) memset((x), 0, s)
> +#define CLEAR(x) CLEAR_P(&(x), sizeof(x))
>  
>  struct buffer {
>  	void   *start;
> @@ -46,22 +48,206 @@ static void xioctl(int fh, unsigned long int request, void *arg)
>  	}
>  }
>  
> +/* Used by the multi thread capture version */
> +struct buffer_queue {
> +	struct v4l2_buffer *buffers;
> +	int buffers_size;
> +
> +	int read_pos;
> +	int write_pos;
> +	int n_frames;
> +
> +	int fd;
> +
> +	pthread_mutex_t mutex;
> +	pthread_cond_t buffer_cond;
> +};
> +
> +/* Gets a buffer and puts it in the buffers list at write position, then
> + * notifies the consumer that a new buffer is ready to be used */
> +static void *produce_buffer (void * p)
> +{
> +	struct buffer_queue 		*bq;
> +	fd_set				fds;
> +	struct timeval			tv;
> +	int				i;
> +	struct v4l2_buffer		*buf;
> +	int				r;
> +
> +	bq = p;
> +
> +	for (i = 0; i < bq->n_frames; i++) {
> +		printf ("Prod: %d\n", i);
> +		buf = &bq->buffers[bq->write_pos % bq->buffers_size];
> +		do {
> +			FD_ZERO(&fds);
> +			FD_SET(bq->fd, &fds);
> +
> +			/* Timeout. */
> +			tv.tv_sec = 2;
> +			tv.tv_usec = 0;
> +
> +			r = select(bq->fd + 1, &fds, NULL, NULL, &tv);
> +		} while ((r == -1 && (errno == EINTR)));
> +		if (r == -1) {
> +			perror("select");
> +			pthread_exit (NULL);
> +			return NULL;
> +		}
> +
> +		CLEAR_P(buf, sizeof(struct v4l2_buffer));
> +		buf->type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
> +		buf->memory = V4L2_MEMORY_MMAP;
> +		xioctl(bq->fd, VIDIOC_DQBUF, buf);
> +
> +		pthread_mutex_lock (&bq->mutex);
> +		bq->write_pos++;
> +		printf ("Prod: %d (done)\n", i);
> +		pthread_cond_signal (&bq->buffer_cond);
> +		pthread_mutex_unlock (&bq->mutex);
> +
> +	}
> +
> +	pthread_exit (NULL);
> +}
> +
> +/* will create a separate thread that will produce the buffers and put
> + * into a circular array while this same thread will get the buffers from
> + * this array and 'render' them */
> +static int capture_threads (int fd, struct buffer *buffers, int bufpool_size,
> +			struct v4l2_format fmt, int n_frames,
> +			char *out_dir, int sleep_ms)
> +{
> +	struct v4l2_buffer		buf;
> +	unsigned int			i;
> +	struct buffer_queue		buf_queue;
> +	pthread_t			producer;
> +	char				out_name[25 + strlen(out_dir)];
> +	FILE				*fout;
> +	struct timespec			sleeptime;
> +
> +	if (sleep_ms) {
> +		sleeptime.tv_sec = sleep_ms / 1000;
> +		sleeptime.tv_nsec = (sleep_ms % 1000) * 1000000;
> +	}
> +
> +	buf_queue.buffers_size = bufpool_size * 2;
> +	buf_queue.buffers = calloc(buf_queue.buffers_size,
> +				   sizeof(struct v4l2_buffer));
> +	buf_queue.fd = fd;
> +	buf_queue.read_pos = 0;
> +	buf_queue.write_pos = 0;
> +	buf_queue.n_frames = n_frames;
> +	pthread_mutex_init (&buf_queue.mutex, NULL);
> +	pthread_cond_init (&buf_queue.buffer_cond, NULL);
> +
> +	pthread_create (&producer, NULL, produce_buffer, &buf_queue);
> +
> +	for (i = 0; i < n_frames; i++) {
> +		printf ("Read: %d\n", i);
> +
> +		/* wait for a buffer to be available in the queue */
> +		pthread_mutex_lock (&buf_queue.mutex);
> +		while (buf_queue.read_pos == buf_queue.write_pos) {
> +			pthread_cond_wait (&buf_queue.buffer_cond,
> +					   &buf_queue.mutex);
> +		}
> +		pthread_mutex_unlock (&buf_queue.mutex);
> +
> +		if (sleep_ms)
> +			nanosleep (&sleeptime, NULL);
> +
> +		sprintf(out_name, "%s/out%03d.ppm", out_dir, i);
> +		fout = fopen(out_name, "w");
> +		if (!fout) {
> +			perror("Cannot open image");
> +			exit(EXIT_FAILURE);
> +		}
> +		fprintf(fout, "P6\n%d %d 255\n",
> +			fmt.fmt.pix.width, fmt.fmt.pix.height);
> +		buf = buf_queue.buffers[buf_queue.read_pos %
> +					buf_queue.buffers_size];
> +		fwrite(buffers[buf.index].start, buf.bytesused, 1, fout);
> +		fclose(fout);
> +
> +		xioctl(fd, VIDIOC_QBUF, &buf);
> +
> +		pthread_mutex_lock (&buf_queue.mutex);
> +		buf_queue.read_pos++;
> +		printf ("Read: %d (done)\n", i);
> +		pthread_cond_signal (&buf_queue.buffer_cond);
> +		pthread_mutex_unlock (&buf_queue.mutex);
> +	}
> +
> +	pthread_mutex_destroy (&buf_queue.mutex);
> +	pthread_cond_destroy (&buf_queue.buffer_cond);
> +	free (buf_queue.buffers);
> +	return 0;
> +}
> +
> +static int capture_loop (int fd, struct buffer *buffers, struct v4l2_format fmt,
> +			int n_frames, char *out_dir)
> +{
> +	struct v4l2_buffer		buf;
> +	unsigned int			i;
> +	struct timeval			tv;
> +	int				r;
> +	fd_set				fds;
> +	FILE				*fout;
> +	char				out_name[25 + strlen(out_dir)];
> +
> +	for (i = 0; i < n_frames; i++) {
> +		do {
> +			FD_ZERO(&fds);
> +			FD_SET(fd, &fds);
> +
> +			/* Timeout. */
> +			tv.tv_sec = 2;
> +			tv.tv_usec = 0;
> +
> +			r = select(fd + 1, &fds, NULL, NULL, &tv);
> +		} while ((r == -1 && (errno == EINTR)));
> +		if (r == -1) {
> +			perror("select");
> +			return errno;
> +		}
> +
> +		CLEAR(buf);
> +		buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
> +		buf.memory = V4L2_MEMORY_MMAP;
> +		xioctl(fd, VIDIOC_DQBUF, &buf);
> +
> +		sprintf(out_name, "%s/out%03d.ppm", out_dir, i);
> +		fout = fopen(out_name, "w");
> +		if (!fout) {
> +			perror("Cannot open image");
> +			exit(EXIT_FAILURE);
> +		}
> +		fprintf(fout, "P6\n%d %d 255\n",
> +			fmt.fmt.pix.width, fmt.fmt.pix.height);
> +		fwrite(buffers[buf.index].start, buf.bytesused, 1, fout);
> +		fclose(fout);
> +
> +		xioctl(fd, VIDIOC_QBUF, &buf);
> +	}
> +	return 0;
> +}
> +
>  static int capture(char *dev_name, int x_res, int y_res, int n_frames,
> -		   char *out_dir)
> +		   char *out_dir, int block, int threads, int sleep_ms)
>  {
>  	struct v4l2_format		fmt;
>  	struct v4l2_buffer		buf;
>  	struct v4l2_requestbuffers	req;
>  	enum v4l2_buf_type		type;
> -	fd_set				fds;
> -	struct timeval			tv;
> -	int				r, fd = -1;
> +	int				fd = -1;
>  	unsigned int			i, n_buffers;
> -	char				out_name[25 + strlen(out_dir)];
> -	FILE				*fout;
>  	struct buffer			*buffers;
>  
> -	fd = v4l2_open(dev_name, O_RDWR | O_NONBLOCK, 0);
> +	if (block)
> +		fd = v4l2_open(dev_name, O_RDWR, 0);
> +	else
> +		fd = v4l2_open(dev_name, O_RDWR | O_NONBLOCK, 0);
>  	if (fd < 0) {
>  		perror("Cannot open device");
>  		exit(EXIT_FAILURE);
> @@ -119,40 +305,11 @@ static int capture(char *dev_name, int x_res, int y_res, int n_frames,
>  	type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
>  
>  	xioctl(fd, VIDIOC_STREAMON, &type);
> -	for (i = 0; i < n_frames; i++) {
> -		do {
> -			FD_ZERO(&fds);
> -			FD_SET(fd, &fds);
> -
> -			/* Timeout. */
> -			tv.tv_sec = 2;
> -			tv.tv_usec = 0;
> -
> -			r = select(fd + 1, &fds, NULL, NULL, &tv);
> -		} while ((r == -1 && (errno == EINTR)));
> -		if (r == -1) {
> -			perror("select");
> -			return errno;
> -		}
> -
> -		CLEAR(buf);
> -		buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
> -		buf.memory = V4L2_MEMORY_MMAP;
> -		xioctl(fd, VIDIOC_DQBUF, &buf);
> -
> -		sprintf(out_name, "%s/out%03d.ppm", out_dir, i);
> -		fout = fopen(out_name, "w");
> -		if (!fout) {
> -			perror("Cannot open image");
> -			exit(EXIT_FAILURE);
> -		}
> -		fprintf(fout, "P6\n%d %d 255\n",
> -			fmt.fmt.pix.width, fmt.fmt.pix.height);
> -		fwrite(buffers[buf.index].start, buf.bytesused, 1, fout);
> -		fclose(fout);
> -
> -		xioctl(fd, VIDIOC_QBUF, &buf);
> -	}
> +	if (threads)
> +		capture_threads(fd, buffers, 2, fmt, n_frames, out_dir,
> +				sleep_ms);
> +	else
> +		capture_loop(fd, buffers, fmt, n_frames, out_dir);
>  
>  	type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
>  	xioctl(fd, VIDIOC_STREAMOFF, &type);
> @@ -179,6 +336,9 @@ static const struct argp_option options[] = {
>  	{"xres",	'x',	"XRES",		0,	"horizontal resolution", 0},
>  	{"yres",	'y',	"YRES",		0,	"vertical resolution", 0},
>  	{"n-frames",	'n',	"NFRAMES",	0,	"number of frames to capture", 0},
> +	{"thread-enable", 't',	"THREADS",	0,	"if different threads should capture and save", 0},
> +	{"blockmode-enable", 'b', "BLOCKMODE",	0,	"if blocking mode should be used", 0},
> +	{"sleep-time",	's',	"SLEEP",	0,	"how long should the consumer thread sleep to simulate the processing of a buffer (in ms)"},
>  	{ 0, 0, 0, 0, 0, 0 }
>  };
>  
> @@ -188,6 +348,9 @@ static char	*out_dir = ".";
>  static int	x_res = 640;
>  static int	y_res = 480;
>  static int	n_frames = 20;
> +static int	threads = 0;
> +static int	block = 0;
> +static int	sleep_ms = 0;
>  
>  static error_t parse_opt(int k, char *arg, struct argp_state *state)
>  {
> @@ -215,6 +378,17 @@ static error_t parse_opt(int k, char *arg, struct argp_state *state)
>  		if (val)
>  			n_frames = val;
>  		break;
> +	case 't':
> +		threads = 1;
> +		break;
> +	case 'b':
> +		block = 1;
> +		break;
> +	case 's':
> +		val = atoi(arg);
> +		if (val)
> +			sleep_ms = val;
> +		break;
>  	default:
>  		return ARGP_ERR_UNKNOWN;
>  	}
> @@ -232,5 +406,6 @@ int main(int argc, char **argv)
>  {
>  	argp_parse(&argp, argc, argv, 0, 0, 0);
>  
> -	return capture(dev_name, x_res, y_res, n_frames, out_dir);
> +	return capture(dev_name, x_res, y_res, n_frames, out_dir, block,
> +		       threads, sleep_ms);
>  }
>