pcap_breakloop(3) - NetBSD Manual Pages

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PCAP_BREAKLOOP(3)                                            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  con-
       sole  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 com-
       pletes.

       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  termi-
       nated  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 subse-
       quent call will return PCAP_ERROR_BREAK and clear the flag.


SEE ALSO

       pcap(3)



                                 25 July 2018                PCAP_BREAKLOOP(3)