Re: mutex and exeptions

[lutterdc@cs.purdue.edu (David Lutterkort)]

Sascha Ziemann <szi@aibon.ping.de> writes
> 
> Hi,
> 
> when I protect a chunk with a mutex I have to catch all exeptions in
> order to unlock the mutex in a case of an exeptions. After this I have
> the throw the same exeption again. But then the source of the exeption
> is my exeption handler and not the place, where the exeption has been
> originally thrown. Is it possible to bypass the orginal thrown
> exeption in such a case?
> 

As far as I understand the way exceptions work in Guile, this problem can
be solved by using dynamic-wind:
(dynamc-wind
	(lambda () ; before
	 ... lock the mutexes ...)
	(lambda () ; thunk
	 ... do all this dangerous stuff ...)
	(lambda () ; after
	 ... unlock mutexes ...))
the after part is always called, even when thunk has a non-local exit (as
in an exception). See R5RS for a detailed description of dynamic-wind.

David