libpcap-1.3.0/pcap_breakloop.3pcap

.\" @(#) $Header: /tcpdump/master/libpcap/pcap_breakloop.3pcap,v 1.3 2008-04-06 02:53:21 guy Exp $
.\"
.\" Copyright (c) 1994, 1996, 1997
.\"	The Regents of the University of California.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that: (1) source code distributions
.\" retain the above copyright notice and this paragraph in its entirety, (2)
.\" distributions including binary code include the above copyright notice and
.\" this paragraph in its entirety in the documentation or other materials
.\" provided with the distribution, and (3) all advertising materials mentioning
.\" features or use of this software display the following acknowledgement:
.\" ``This product includes software developed by the University of California,
.\" Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
.\" the University nor the names of its contributors may be used to endorse
.\" or promote products derived from this software without specific prior
.\" written permission.
.\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
.\" WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
.\"
.TH PCAP_BREAKLOOP 3PCAP "5 April 2008"
.SH NAME
pcap_breakloop \- force a pcap_dispatch() or pcap_loop() call to return
.SH SYNOPSIS
.nf
.ft B
#include <pcap/pcap.h>
.ft
.LP
.ft B
void pcap_breakloop(pcap_t *);
.ft
.fi
.SH DESCRIPTION
.B pcap_breakloop()
sets a flag that will force
.B pcap_dispatch()
or
.B 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.
.PP
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.
.PP
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.
.ft B
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.
.PP
Note also that, in a multi-threaded application, if one thread is
blocked in
.BR pcap_dispatch() ,
.BR pcap_loop() ,
.BR pcap_next() ,
or
.BR pcap_next_ex() ,
a call to
.B 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.
.ft R
.PP
Note that
.B pcap_next()
and
.B pcap_next_ex()
will, on some platforms, loop reading packets from the OS; that loop
will not necessarily be terminated by a signal, so
.B pcap_breakloop()
should be used to terminate packet processing even if
.B pcap_next()
or
.B pcap_next_ex()
is being used.
.PP
.B pcap_breakloop()
does not guarantee that no further packets will be processed by
.B pcap_dispatch()
or
.B pcap_loop()
after it is called; at most one more packet might be processed.
.PP
If \-2 is returned from
.B pcap_dispatch()
or
.BR 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 \-2 and clear the flag.
.SH SEE ALSO
pcap(3PCAP), pcap_loop(3PCAP), pcap_next_ex(3PCAP)