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Full Discussion: Problem with signal handler and interrupted system call
Top Forums Programming Problem with signal handler and interrupted system call Post 302280302 by otheus on Monday 26th of January 2009 12:45:58 PM
Old 01-26-2009
Quote:
Code:
       retval = read(fd, &data, sizeof(unsigned long));
        if (retval == -1) {
            perror("read");
            exit(errno);
        }

That's your problem, more or less. If read() is interrupted by a system call, it returns -1, sets errno to EINTR. Your program itself does the perror and exiting, not read(). So just check if the return is -1 and errno != EINTR and restart the loop (for instance). You'll have to handle the logic for the ioctls and what not, too, or every now and then, your signal will interrupt the ioctl and exit.
 

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LEARN ABOUT V7

pcap_breakloop

PCAP_BREAKLOOP(3PCAP)													     PCAP_BREAKLOOP(3PCAP)

NAME

       pcap_breakloop - force a pcap_dispatch() or pcap_loop() call to return

SYNOPSIS

       #include <pcap/pcap.h>

       void pcap_breakloop(pcap_t *);

DESCRIPTION

       pcap_breakloop()  sets  a flag that will force pcap_dispatch() or pcap_loop() to return rather than looping; they will return the number of
       packets that have been processed so far, or -2 if no packets have been processed so far.

       This routine is safe to use inside a signal handler on UNIX or a console control handler on Windows, as it  merely  sets  a  flag  that	is
       checked within the loop.

       The  flag  is  checked in loops reading packets from the OS - a signal by itself will not necessarily terminate those loops - as well as in
       loops processing a set of packets returned by the OS.  Note that if you are catching signals on UNIX systems that support restarting system
       calls  after a signal, and calling pcap_breakloop() in the signal handler, you must specify, when catching those signals, that system calls
       should NOT be restarted by that signal.	Otherwise, if the signal interrupted a call reading packets in a live capture,	when  your  signal
       handler	returns  after calling pcap_breakloop(), the call will be restarted, and the loop will not terminate until more packets arrive and
       the call completes.

       Note also that, in a multi-threaded application, if one thread is blocked in pcap_dispatch(), pcap_loop(), pcap_next(), or  pcap_next_ex(),
       a  call to pcap_breakloop() in a different thread will not unblock that thread; you will need to use whatever mechanism the OS provides for
       breaking a thread out of blocking calls in order to unblock the thread, such as thread cancellation in systems that support POSIX threads.

       Note that pcap_next() and pcap_next_ex() will, on some platforms, loop reading packets from the OS; that loop will not necessarily be  ter-
       minated by a signal, so pcap_breakloop() should be used to terminate packet processing even if pcap_next() or pcap_next_ex() is being used.

       pcap_breakloop() does not guarantee that no further packets will be processed by pcap_dispatch() or pcap_loop() after it is called; at most
       one more packet might be processed.

       If -2 is returned from pcap_dispatch() or pcap_loop(), the flag is cleared, so a subsequent call will resume reading packets.  If  a  posi-
       tive number is returned, the flag is not cleared, so a subsequent call will return -2 and clear the flag.

SEE ALSO

       pcap(3PCAP), pcap_loop(3PCAP), pcap_next_ex(3PCAP)

								   5 April 2008 					     PCAP_BREAKLOOP(3PCAP)
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