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1 office 1 .\" Copyright (c) 1994, 1996, 1997
2 .\" The Regents of the University of California. All rights reserved.
3 .\"
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5 .\" modification, are permitted provided that: (1) source code distributions
6 .\" retain the above copyright notice and this paragraph in its entirety, (2)
7 .\" distributions including binary code include the above copyright notice and
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10 .\" features or use of this software display the following acknowledgement:
11 .\" ``This product includes software developed by the University of California,
12 .\" Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
13 .\" the University nor the names of its contributors may be used to endorse
14 .\" or promote products derived from this software without specific prior
15 .\" written permission.
16 .\" THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
17 .\" WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
18 .\" MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
19 .\"
20 .TH PCAP_BREAKLOOP 3PCAP "5 April 2008"
21 .SH NAME
22 pcap_breakloop \- force a pcap_dispatch() or pcap_loop() call to return
23 .SH SYNOPSIS
24 .nf
25 .ft B
26 #include <pcap/pcap.h>
27 .ft
28 .LP
29 .ft B
30 void pcap_breakloop(pcap_t *);
31 .ft
32 .fi
33 .SH DESCRIPTION
34 .B pcap_breakloop()
35 sets a flag that will force
36 .B pcap_dispatch()
37 or
38 .B pcap_loop()
39 to return rather than looping; they will return the number of packets
40 that have been processed so far, or \-2 if no packets have been
41 processed so far.
42 .PP
43 This routine is safe to use inside a signal handler on UNIX or a console
44 control handler on Windows, as it merely sets a flag that is checked
45 within the loop.
46 .PP
47 The flag is checked in loops reading packets from the OS - a signal by
48 itself will not necessarily terminate those loops - as well as in loops
49 processing a set of packets returned by the OS.
50 .ft B
51 Note that if you are catching signals on UNIX systems that support
52 restarting system calls after a signal, and calling pcap_breakloop()
53 in the signal handler, you must specify, when catching those signals,
54 that system calls should NOT be restarted by that signal. Otherwise,
55 if the signal interrupted a call reading packets in a live capture,
56 when your signal handler returns after calling pcap_breakloop(), the
57 call will be restarted, and the loop will not terminate until more
58 packets arrive and the call completes.
59 .ft R
60 .PP
61 .ft B
62 Note also that, in a multi-threaded application, if one thread is
63 blocked in pcap_dispatch(), pcap_loop(), pcap_next(), or pcap_next_ex(),
64 a call to pcap_breakloop() in a different thread will not unblock that
65 thread; you will need to use whatever mechanism the OS provides for
66 breaking a thread out of blocking calls in order to unblock the thread,
67 such as thread cancellation in systems that support POSIX threads.
68 .ft R
69 .PP
70 Note that
71 .B pcap_next()
72 and
73 .B pcap_next_ex()
74 will, on some platforms, loop reading packets from the OS; that loop
75 will not necessarily be terminated by a signal, so
76 .B pcap_breakloop()
77 should be used to terminate packet processing even if
78 .B pcap_next()
79 or
80 .B pcap_next_ex()
81 is being used.
82 .PP
83 .B pcap_breakloop()
84 does not guarantee that no further packets will be processed by
85 .B pcap_dispatch()
86 or
87 .B pcap_loop()
88 after it is called; at most one more packet might be processed.
89 .PP
90 If \-2 is returned from
91 .B pcap_dispatch()
92 or
93 .BR pcap_loop() ,
94 the flag is cleared, so a subsequent call will resume reading packets.
95 If a positive number is returned, the flag is not cleared, so a
96 subsequent call will return \-2 and clear the flag.
97 .SH SEE ALSO
98 pcap(3PCAP), pcap_loop(3PCAP), pcap_next_ex(3PCAP)