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Full Discussion: Signals and semaphores
Top Forums Programming Signals and semaphores Post 302450269 by _thomas on Thursday 2nd of September 2010 05:28:21 AM
Old 09-02-2010
Signals and semaphores
I have problem with my application. Application is running on embedded Linux machine. It's basically multiprotocol gateway that connects two industrial Ethernet networks.

We are experiencing some kind of application hang every 2 to 3 days. It seems like both threads are still running but SIGALARM signal is getting lost. I'm not completely sure if this is a case because project is in testing phase and I can't make any application changes until end of a week.SIGALARM is used for counter implementation and it is activated every second.

I have semaphores inside signal handler and inside thread. I have initialized SIGALRM with sigaction and SA_RESTART flag. I suspect this is a reason why we are experiencing counter (or application) hang.

Code:
  void start_timer(void)
    {
       struct sigaction sa;
       struct itimerval timer;

       memset(&sa, 0, sizeof (sa));
 
       sa.sa_handler = &timer_handler;
       sa.sa_flags = SA_RESTART;  
       sigaction(SIGALRM, &sa, NULL);

       timer.it_value.tv_sec = 1;
       timer.it_value.tv_usec = 0;
 
       timer.it_interval.tv_sec = 1;
       timer.it_interval.tv_usec = 0;

       setitimer(ITIMER_REAL, &timer, NULL);
    }


    int main(int  argc, char *argv[])
    {
        //  write log entry
        //  check arguments to main
        //  read files containing parameters  of remote devices 
    
        //  initialise semaphores 
        sem_init(&semCounters, 0, 1);
        sem_init(&semPackets, 0, 1);
        sem_init(&semEvents, 0, 1);
        
        start_timer();
        pthread_create(&thread1, NULL, firstThread, NULL);
        pthread_create(&thread2, NULL, secondThread, NULL);
    
        while(1)
        {            
            //  infinite loop
        }
    
        return 0;
    }

Inside a second thread (secondThread) I have multiple math operation with time counters. All counter are protected with semaphores (semCounter). I'm using same counters inside signal handler! Semaphores are in both locations. Below is an example of use reinitialization of protected variable. This code can be found both in signal handler and in thread.

Code:
sem_wait(&semCounters);
    counter.t4 = 0;
    sem_post(&semCounters);

One more thing. I'm creating other threads inside signal handler but I'm not waiting thread to finish processing. Application has been restarted 4 times so far. Longest running time without hang is three days.
 

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LEARN ABOUT LINUX

pppoe-sniff

PPPOE-SNIFF(8)						      System Manager's Manual						    PPPOE-SNIFF(8)

NAME

       pppoe-sniff - examine network for non-standard PPPoE frames

SYNOPSIS

       pppoe-sniff [options]

DESCRIPTION

       pppoe-sniff listens for likely-looking PPPoE PADR and session frames and deduces extra options required for pppoe(8) to work.

       Some  DSL providers seem to use non-standard frame types for PPPoE frames, and/or require a certain value in the Service-Name field.  It is
       often easier to sniff those values from a machine which can successfully connect rather than try to pry them out of the DSL provider.

       To use pppoe-sniff, you need two computers, a DSL modem and an Ethernet hub (not an Ethernet switch.)

       If the DSL modem normally connects directly to your computer's Ethernet card, connect it to the "uplink" port on the  Ethernet  hub.   Plug
       two  computers into normal ports on the hub.  On one computer, run whatever software the DSL provider gave you on whatever operating system
       the DSL provider supports.  On the other computer, run Linux and log in as root.

       On the Linux machine, put the Ethernet interface into promiscuous mode and start pppoe-sniff.  If the ethernet interface is eth0, for exam-
       ple, type these commands:

	    ifconfig eth0 promisc
	    pppoe-sniff -I eth0

       On  the	other  machine, start your DSL connection as usual.  After a short time, pppoe-sniff should print recommendations for the value of
       PPPOE_EXTRA.  Set this value in /etc/ppp/pppoe.conf.  If pppoe-sniff indicates that something special is required in PPPOE_EXTRA, please e-
       mail this to pppoe@roaringpenguin.com along with the name of your ISP and the manufacturer and model number of your DSL modem.  This infor-
       mation will be collated and provided on the PPPoE web page for users who do not have two computers.

       After pppoe-sniff finishes (or you stop it if it seems hung), remember to turn off promiscuous mode:

	    ifconfig eth0 -promisc

OPTIONS

       -I interface
	      The -I option specifies the Ethernet interface to use.  Under Linux, it is typically eth0 or eth1.  The interface should be "up" and
	      in promiscuous mode before you start pppoe-sniff.

       -V     The -V option causes pppoe-sniff to print its version number and exit.

BUGS

       pppoe-sniff only works on Linux.

AUTHORS

       pppoe-sniff was written by David F. Skoll <dfs@roaringpenguin.com>.

       The pppoe home page is http://www.roaringpenguin.com/pppoe/.

SEE ALSO

       pppd(8), pppoe(8), pppoe-sniff(8), pppoe-relay(8), /usr/share/doc/pppoe/README.Debian.gz

4th Berkeley Distribution					    3 July 2000 						    PPPOE-SNIFF(8)
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