pcap_breakloop() sets a flag that will force pcap_dispatch(3PCAP)
or pcap_loop(3PCAP) 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 thatsupport restarting system calls after a signal, and callingpcap_breakloop() in the signal handler, you must specify, whencatching those signals, that system calls should NOT be restartedby that signal. Otherwise, if the signal interrupted a callreading packets in a live capture, when your signal handlerreturns after calling pcap_breakloop(), the call will berestarted, and the loop will not terminate until more packetsarrive and the call completes.Note also that, in a multi-threaded application, if one thread isblocked in pcap_dispatch(), pcap_loop(), pcap_next(3PCAP), orpcap_next_ex(3PCAP), a call to pcap_breakloop() in a differentthread 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.
This page is part of the libpcap (packet capture library)
project. Information about the project can be found at
⟨http://www.tcpdump.org/⟩. If you have a bug report for this
manual page, see ⟨http://www.tcpdump.org/#patches⟩. This page
was obtained from the project's upstream Git repository
⟨https://github.com/the-tcpdump-group/libpcap.git⟩ on 2021-04-01.
(At that time, the date of the most recent commit that was found
in the repository was 2021-03-31.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
25 July 2018 PCAP_BREAKLOOP(3PCAP)