Problems designing a signal handler in UNIX
CodeGuru Home VC++ / MFC / C++ .NET / C# Visual Basic VB Forums Developer.com
Results 1 to 5 of 5

Thread: Problems designing a signal handler in UNIX

  1. #1
    Join Date
    Sep 2008
    Posts
    26

    Problems designing a signal handler in UNIX

    I'm trying to create a signal handler thread to handle SIGALRM signals.

    The main thread calls the following function before creating any other threads

    Code:
    pthread_t Timer::Init(long _clock_interval_musec)
    {
    	// Set interval.
    	clock_interval = _clock_interval_musec;
    	// This is called while in a single threaded environment.
    	// Main thread masks alarm.
    	sigset_t alarm_off_mask;
    	if ((sigemptyset(&alarm_off_mask) == -1) || (sigaddset(&alarm_off_mask, SIGALRM) == -1))
    	   perror("Failed to initialize the signal set");
    	if (pthread_sigmask(SIG_BLOCK, &alarm_off_mask, NULL) == -1)
    	   perror("Failed to block SIGALRM");
    	// Now call a new thread which handles alarm signals.
    	pthread_t retID;
    	pthread_create(&retID, NULL, TimerHandlerThread, NULL);
    	// Return id of thread responsible for managing alarm signals.
    	return retID;
    }
    As you can see, I block the alarm signal.

    The spawned signal handler thread has the following Run function

    Code:
    void* Timer::TimerHandlerThread(void* args)
    {
    	// Change granualirity of alarm.
    	itimerval tv;
    	tv.it_interval.tv_sec  = clock_interval / USECS_IN_SECS;
    	tv.it_interval.tv_usec = clock_interval % USECS_IN_SECS;
    
    	setitimer(ITIMER_REAL, &tv, NULL);
    	// Unmask alarm signals in this thread.
    	sigset_t sigset;
    	if ((sigemptyset(&sigset) == -1) || (sigaddset(&sigset, SIGALRM) == -1))
            perror("Failed to add signal to wait for");
    
    	Timer currentTime;
    	int sig;
    	while (1) 
    	{
     		/* wait for a signal to arrive */
    		sigwait(&sigset, &sig);
    	       std::cout << "we are here\n";
    		if (sig == SIGALRM && g_timerQueue.size() > 0)
    		{
    			currentTime.Set(0);
    			// Handle if needed
    			g_mutex.P();
    			if (*(g_timerQueue.front()) < currentTime)
    			{
    				g_timerQueue.front()->Event_Handler();
    				std::pop_heap(g_timerQueue.begin(), g_timerQueue.end());
    				g_timerQueue.pop_back();
    			}
    			g_mutex.V();
    		}
    	}
    
    	return NULL;
    }
    Sigwait never returns ("we are here" never prints).

    clock_interval is 50.

    Is the timer not firing?
    Did I not set my interval correctly?
    Did I not proper block the signals ensuring the that the default handler would not take care of them?

    Any help is welcome.

  2. #2
    Join Date
    Sep 2008
    Posts
    26

    Re: Problems designing a signal handler in UNIX

    If the lack of replies is due to the question not being clear, please do say so.

  3. #3
    Join Date
    Nov 2003
    Posts
    1,797

    Re: Problems designing a signal handler in UNIX

    Try setting both tv.it_interval and tv.it_value.

    You should flush cout if you want to see the output immediately.

    gg

  4. #4
    Join Date
    Jan 2010
    Posts
    12

    Re: Problems designing a signal handler in UNIX

    I'm not familiar with Unix style threading (or the Posix pthreads library) - so I'm probably not the person to help, but don't you need to add the timer signal to your signal set? (sigaddset)

  5. #5
    Join Date
    Nov 2003
    Posts
    1,797

    Re: Problems designing a signal handler in UNIX

    Signal handlers and threads don't mix well. There's little you can do in a signal handler, and there's no control of which thread (if any) the signal handler is executed on.

    To have a thread deal with particular signals, you have to block that signal in all threads, then a single thread can use sigwait() to determine if the signal is pending and act on it.
    See Examples section here: http://www.opengroup.org/onlinepubs/...d_sigmask.html

    gg

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  


Windows Mobile Development Center


Click Here to Expand Forum to Full Width

This is a CodeGuru survey question.


Featured


HTML5 Development Center