Re: [libdc1394-devel] Threading libdc1394

[Mark M. <mar...@po...>]

Hi Thomas,

I'm using a similar setup: main thread is used to set camera settings =20=

(like brightness, contrast) through the GUI, while dequeue/enqueue is =20=

handled by a separate capture thread.

Examining my apps logfiles, I see once in a while I receive an error =20
when trying to read or set some camera setting.

I am wondering what's the cause for this. Is it ok to set camera =20
values from one thread and enqueue/dequeue from another without some =20
locking mechanism, or might that be the cause of the errors.

Does this happen to you too, are you serializing commands sent to the =20=

camera?

Best regards from Konstanz
Mark

On 22.02.2007, at 12:53, Tho...@t-... wrote:

> Hey!
> Threading the libdc1394 has not caused any
> problems for me. I am using it to record and display images in a
> Qt-based application.
>
> Basically I got:
> 1) main thread
> Which initializes the camera like your exammple
>
> 2) event
> thread
> Which i.e. starts the capture process when I hit my
> "Start Capture" button.
>
> It also takes care of
> setting camera features, like brightness, contrast, sharpness =20
> through my
> config dialog.
>
> 3) capture thread
> Does the dequeue
> enqueue DMA buffer handling and converts the image data to RGB. When a
> new frame is ready it emits a callback to the render thread.
>
> 4) render thread
> Fetches the last image data and displays it as
> an OpenGL texture.
>
> Didn't give me a single crash (outside of
> my own code) or problem. Only thing happened to me that some settings
> could not be applied when a capture process is already running. In =20
> that
> case I had to properly stop the capture thread before doing the
> changes.
>
> Hope this helps!
>
> Thomas W=F6llert, cand.
> M.Sc.
> Munich University of Applied Sciences
>
>
> /**
> *----------------------------------------------------------
> */
> So I've moved on to attempting to thread with libdc1394.  I can't
> find
> a good description in the list or the faq on what I can and
> can't do
> between multiple threads though so I cooked up some
> semi-specific
> pseudocode on how I plan to implement this.
>
> If anyone has any opinions let me know. I haven't actually tried
> the
> corresponding real code for this yet, but I should have
> initial
> results in a couple hours.
>
> main thread:
>
> void
> init()
> {
> 	create_run_lock() ;
> 	create_camera_mutex() ;
> 	create_img_cond_lock() ;
> 	frame =3D
> NULL ;
> 	stamp =3D 0 ;
> 	last_stamp =3D 0 ;
>
> 	create_reader_thread() ;
> }
>
> void
> read_image()
> {
> 	lock( mutex )
> 		while( frame =3D=3D NULL && stamp =3D=3D
> last_stamp )
> 			cond_wait( new_img_cond, mutex ) ;
>
>
>           last_stamp =3D stamp ;
> 		use_image() ;
>
> 	unlock(
> mutex ) ;
> }
>
> void
> set_gain()
> {
> 	lock(
> camera_mutex ) ;
> 		change_feature() ;
> 	unlock( camera_mutex )
> ;
> }
>
> ----------------
>
> reader thread:
>
> Loop:
> 	lock( camera_mutex ) ;
> 		if( stop_running )
> 		{
> 			break ;
> 		}
>
> 		if( read_frame !=3D NULL )
> 		{
> 			enqueue_frame( read_frame ) ;
> 		}
>
> 		dequeue_frame( read_frame ) ;
> 	unlock( camera_mutex ) ;
>
> 	try_lock( mutex ) ;
> 	if( locked )
> 	{
> 		temp_frame =3D frame ;
> 		frame =3D read_frame ;
> 		read_frame =3D
> frame ;
> 		stamp++ ;
> 		unlock( mutex ) ;
> 		cond_signal(
> new_img_cond ) ;
> 	}
>
> 	lock( run_mutex ) ;
>
> keep_running =3D running ;
> 	unlock( run_mutex ) ;
> End loop
>
> exit_thread() ;
>
>
>
> ----------------------------------------------------------------------=20=

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