Subj : Using SIGALRM with pthread
To   : comp.programming.threads
From : gc
Date : Wed Jul 27 2005 03:39 pm

Hi all,

I am writting an application on Linux 2.4.28 using C++ which involvs
the use of ALARM signal handling in a multi-threaded program.

In my application, there are basically two threads (threads A an B),
both started by the main thread. The main thread here doesn't do much
job here. Thread A and B share some STL data structures, maps and
lists,
and there is a unique semaphore (implemented based on the pthread_mutex

and pthread_cond) assocaiated with every data structure.

I also have a condition variable associated with a pthread_mutex and a
pthread_cond. Thread A waits on the condtion variable
(pthread_cond_wait) while the Thread B updates the condition variable
and sends signals (pthread_cond_signal) to wake up the waiting thead.

At the same time, I need to use an ALARM signal (SIGALRM) in thread A
to invoke a periodical even handler. I use the signal() function to
install the handler for SIGALRM in thread A's constructor. In the
SIGALRM handler, I also need to access some variables and data
structures from thread A.

What frustrates me is that, without turning on the ALARM signal,
everything goes well. Whenever I turn on the ALARM signal, I get all
kinds of werid errors related to pthread_mutexes. For instance,
segmentation fault on pthread_mutex_unlock (unlock the mutex for the
conditional variable), or sometimes thread B gets blocked on
pthread_mutex_unlock (unlock does not return), or sometimes the whole
program halts.

These bugs all seem to come from the pthread library, but I think
there is something wrong in my code.

So, I am not sure if anybody has experience with this or similiar
situations. Or does anybody have good resources related to using
threads and signals at the same time?

Thanks for your help!

gc

.