1PCAP_BREAKLOOP(3PCAP)                                    PCAP_BREAKLOOP(3PCAP)
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NAME

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

9       #include <pcap/pcap.h>
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11       void pcap_breakloop(pcap_t *);
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DESCRIPTION

14       pcap_breakloop()  sets  a  flag that will force pcap_dispatch(3PCAP) or
15       pcap_loop(3PCAP) to return rather than looping; they  will  return  the
16       number  of packets that have been processed so far, or PCAP_ERROR_BREAK
17       if no packets have been processed so far.
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19       This routine is safe to use inside a signal handler on UNIX or  a  con‐
20       sole  control  handler  on  Windows,  as  it merely sets a flag that is
21       checked within the loop.
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23       The flag is checked in loops reading packets from the OS - a signal  by
24       itself will not necessarily terminate those loops - as well as in loops
25       processing a set of packets returned by the OS.  Note that if  you  are
26       catching  signals  on UNIX systems that support restarting system calls
27       after a signal, and calling pcap_breakloop() in the signal handler, you
28       must specify, when catching those signals, that system calls should NOT
29       be restarted by that signal.  Otherwise, if the  signal  interrupted  a
30       call  reading  packets  in  a  live  capture,  when your signal handler
31       returns after calling pcap_breakloop(), the call will be restarted, and
32       the loop will not terminate until more packets arrive and the call com‐
33       pletes.
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35       Note also that, in a  multi-threaded  application,  if  one  thread  is
36       blocked   in   pcap_dispatch(),   pcap_loop(),   pcap_next(3PCAP),   or
37       pcap_next_ex(3PCAP), a call to pcap_breakloop() in a  different  thread
38       will  not unblock that thread.  You will need to use whatever mechanism
39       the OS provides for breaking a thread out of blocking calls in order to
40       unblock the thread, such as thread cancellation or thread signalling in
41       systems that support POSIX threads, or  SetEvent()  on  the  result  of
42       pcap_getevent()  on a pcap_t on which the thread is blocked on Windows.
43       Asynchronous procedure calls will not work  on  Windows,  as  a  thread
44       blocked on a pcap_t will not be in an alertable state.
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46       Note  that pcap_next() and pcap_next_ex() will, on some platforms, loop
47       reading packets from the OS; that loop will not necessarily  be  termi‐
48       nated  by  a  signal,  so  pcap_breakloop() should be used to terminate
49       packet processing even if pcap_next() or pcap_next_ex() is being used.
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51       pcap_breakloop() does not guarantee that no  further  packets  will  be
52       processed by pcap_dispatch() or pcap_loop() after it is called; at most
53       one more packet might be processed.
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55       If PCAP_ERROR_BREAK is returned from  pcap_dispatch()  or  pcap_loop(),
56       the  flag is cleared, so a subsequent call will resume reading packets.
57       If a positive number is returned, the flag is not cleared, so a  subse‐
58       quent call will return PCAP_ERROR_BREAK and clear the flag.
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SEE ALSO

61       pcap(3PCAP)
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65                                 25 July 2018            PCAP_BREAKLOOP(3PCAP)
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