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.\" @(#) $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.
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.\" ``This product includes software developed by the University of California,
.\" Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
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.\"
.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.
.ft R
.PP
.ft B
Note also that, in a multi-threaded application, if one thread is
blocked in pcap_dispatch(), pcap_loop(), pcap_next(), or pcap_next_ex(),
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 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)
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