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RE: pthread_cancel and pthread_mutex_lock
- From: Simon Gerblich <sgerblich at daronmont dot com dot au>
- To: Rian Hunter <rian at thelaststop dot net>
- Cc: pthreads-win32 at sources dot redhat dot com
- Date: Tue, 17 Feb 2004 09:40:51 +1030
- Subject: RE: pthread_cancel and pthread_mutex_lock
Rian,
Have you worked out your problem? It looks like no-one else has answered
you.
I'd recommend you get the book "Programming with POSIX Threads" by Butenhof.
Also have a look at http://www.unix-systems.org/single_unix_specification/
for the pthread function specifications
A locked mutex should not act as a cancellation point.
I don't use and have not tried PTHREAD_CANCEL_ASYNCHRONOUS. I use
PTHREAD_CANCEL_DEFERRED.
A mutex should be locked and then unlocked in the same thread normally. I'm
not sure what PTHREAD_CANCEL_ASYNCHRONOUS should do.
I know that the pthreadsWin32 works fine for PTHREAD_CANCEL_DEFERRED.
If a thread locks a mutex and then calls a cancellation point the thread
should have a pthread_cancel_push() function to push a cancellation routine
onto the cancellation cleanup stack and the cancellation routine should
unlock the mutex.
Simon
> -----Original Message-----
> From: Rian Hunter [SMTP:rian@thelaststop.net]
> Sent: Wednesday, February 11, 2004 10:38 AM
> To: pthreads-win32@sources.redhat.com
> Subject: pthread_cancel and pthread_mutex_lock
>
> Hello!
>
> >From reading the mailing list archives i found out that at one point in
> the pthreads-win32 library pthread_mutex_lock acted as a cancellation
> point, but since then that was removed. I have a thread that needs to be
> cancelled during a pthread_mutex_lock, so naturally i would have to set
> the cancel type to PTHREAD_CANCEL_ASYNCHRONOUS as per the new behavior.
> I'm not sure if pthread_mutex_lock can be asynchronously cancelled, but
> i'm having a problem with code similar to this:
>
> ------------------
> #include <pthread.h>
> #include <stdio.h>
>
> pthread_mutex_t inputLock;
>
> void *t2(void *threadid) {
> pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, NULL);
> printf("created \n");
>
> /* waits to be cancelled here */
> pthread_mutex_lock(&inputLock);
> /* never gets here */
> printf("dead\n");
> return 0;
> }
>
> int main() {
> pthread_t sender;
> int i;
>
> /* initialize and lock mutex */
> pthread_mutex_init(&inputLock, NULL);
> pthread_mutex_lock(&inputLock);
>
> pthread_create(&sender, NULL, t2, NULL);
>
> /* psuedo sleep function */
> for(i = 0;i <10000000; i++) {}
>
> printf("slept and thread created\n");
>
> /* cancel thread and wait for termination */
> pthread_cancel(sender);
> pthread_join(sender, NULL);
>
> /* check if thread was cancelled */
> printf("successfully canceled thread\n");
>
> /* test lock for continued operation */
> pthread_mutex_unlock(&inputLock);
> pthread_mutex_lock(&inputLock);
>
> /* signify correct execution */
> printf("all done\n");
>
> return 0;
> }
>
> ----------
>
> On FreeBSD the code executes correctly, at least i assume it is the
> correct behavior of a pthreads implementation. On windows it just
> freezes after it prints "created". I appreciate any help! thank you!
> -rian