[linux-dvb] Re: More V4 Video API Q's

[Holger Waechtler <holger@qanu.de>]

Rob.McConnell@Zarlink.Com wrote:

> Now the question is should the corresponding pthread_cleanup_pop be placed
> at the same level as the push or at a higher level to ensure the cleanup
> handler is removed properly.
>
> e.g.  pthread_cleanup_push(cleanup_handler, NULL);
>
>      ioctl(DVB_VIDEO_GET_EVENT, ......);      [BLOCKED]
>
>      pthread_cleanup_pop(0);
>
> Here if another thread/process calls pthread_cancel to cancel this thread,
> then it will exit immediately before it gets to pthread_cleanup_pop.  The
> man page recommends keeping the push/pop calls in the same function, but
> I'm not convinced of this.
>
> Any comments?
>  
Maybe you want to take a look into the push/pop() declaration and 
implementation: they are macros and start a new {}-block:

-------------------- /usr/include/pthread.h ------------------------

/* Install a cleanup handler: ROUTINE will be called with arguments ARG
  when the thread is cancelled or calls pthread_exit.  ROUTINE will also
  be called with arguments ARG when the matching pthread_cleanup_pop
  is executed with non-zero EXECUTE argument.
  pthread_cleanup_push and pthread_cleanup_pop are macros and must always
  be used in matching pairs at the same nesting level of braces. */

#define pthread_cleanup_push(routine,arg) \
 { struct _pthread_cleanup_buffer 
_buffer;                                   \
   _pthread_cleanup_push (&_buffer, (routine), (arg));

extern void _pthread_cleanup_push (struct _pthread_cleanup_buffer *__buffer,
                                  void (*__routine) (void *),
                                  void *__arg) __THROW;

/* Remove a cleanup handler installed by the matching pthread_cleanup_push.
  If EXECUTE is non-zero, the handler function is called. */

#define pthread_cleanup_pop(execute) \
   _pthread_cleanup_pop (&_buffer, (execute)); }

extern void _pthread_cleanup_pop (struct _pthread_cleanup_buffer *__buffer,
                                 int __execute) __THROW;

-----------------------------

So they definitely need to live in the same function.

Holger