Updated: 2021/Apr/14


PCAP_BREAKLOOP(3)          Library Functions Manual          PCAP_BREAKLOOP(3)



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(3) or
       pcap_loop(3) to return rather than looping; they will return the number
       of packets that have been processed so far, or PCAP_ERROR_BREAK 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(3), or
       pcap_next_ex(3), 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 or thread signalling in
       systems that support POSIX threads, or SetEvent() on the result of
       pcap_getevent() on a pcap_t on which the thread is blocked on Windows.
       Asynchronous procedure calls will not work on Windows, as a thread
       blocked on a pcap_t will not be in an alertable state.

       Note that pcap_next() and pcap_next_ex() will, on some platforms, loop
       reading packets from the OS; that loop will not necessarily be
       terminated 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 PCAP_ERROR_BREAK is returned from pcap_dispatch() or pcap_loop(),
       the flag is cleared, so a subsequent call will resume reading packets.
       If a positive number is returned, the flag is not cleared, so a
       subsequent call will return PCAP_ERROR_BREAK and clear the flag.

SEE ALSO
       pcap(3)



                                 25 July 2018                PCAP_BREAKLOOP(3)