Re: [fuse-devel] some newbie-questions

[Luis F. <lui...@gm...>]

On Mon, Nov 24, 2008 at 2:13 PM, Santiago <sa...@gm...> wrote:
> Hello
>
>> > Well, I think, my functions are reentrant, but I don't know yet, how I
>> > can prevent fuse from creating threads (only for certain time).
>> > When I change the underlaying filesystem, I'd like to block fuse, until
>> > the new filesystem is mounted.
>> > When I got this, I think my stuff will be thread safe.
>>
>> So, you have to use semaphores. You will not block FUSE, but will
>> block your callbacks.
>
> Sorry for insisting. May be, I don't really understand the environment.
>
> Blocking a single callback seems not to be the problem.
> I think, in parts it's already blocked, cause I do user interaction, but my
> worry is, that fuse could create another thread for a quite different action.
>
> I would like to prevent that, so I need a semaphore, that blocks all my
> callbacks at the same time. Better would be, not blocking all, but some
> selected callbacks together.
> Is there a way in fuse to realize that, or how can I solve that?

You have to do it *in* your code. If you just want to block, not
communication between the threads, you could do something like it:


#include <pthread.h>
pthread_mutex_t mylock = PTHREAD_MUTEX_INITIALIZER;

pthread_mutex_lock(&mylock); // block the others

// do something exclusively

pthread_mutex_unlock(&mylock);

All the conclicting code must be surrounded by the lock/unlock
calls. Beware to provide an unlock to each lock call. A common
error is to fail/forget to unlock a mutex and then, everything
just stops waiting forever.

If you have groups of callbacks where you have to block all the
group when a callback belonging to this group reaches the
critical code, and no matter if a member of a different group
reaches the critical code, then you may declare one different
mutex per group.


Best Regards!

-- 
Luis Otavio de Colla Furquim
Não alimente os pingos
Don't feed the tribbles
http://www.furquim.org/chironfs/