Question

I am writing a multithreaded program and i have this question:
Suppose that, while executing in the main thread, i want to terminate all
child-threads. I can’t just send them a termination signal cause i want them
to free dynamically allocated memory first. Can i define a specific signal handler
function in each thread function that is executed, which in turn is going to call
a cleanup function that i will write to do so? If not how can i accomplish my goal??

Thanks,
Nikos

Answer 1

Look at the man page for pthread_cancel:

When a cancellation requested is acted on, the following steps occur for
thread (in this order):

   1. Cancellation clean-up handlers are popped (in the reverse of the order in
      which they were pushed) and called.  (See pthread_cleanup_push(3).)

   2. Thread-specific data destructors are called, in an unspecified order.  (See
      pthread_key_create(3).)

   3. The thread is terminated.  (See pthread_exit(3).)

So you can use pthread_cancel from your main, provided you have registered you cleanup handlers correctly using the above functions.

(Do read that man page completely though, it has a lot of important information.)

Edit: (from comments) If you plan on using PTHREAD_CANCEL_DEFERRED and need to insert a cancellation point somewhere in your code, then use pthread_testcancel. This function checks if a cancellation was requested. If that is the case, the cancellation is serviced (i.e. that call never returns). Otherwise it has no effect.