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.TH PCAP_BREAKLOOP 3PCAP "25 July 2018"
.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
.BR pcap_breakloop ()
sets a flag that will force
.BR pcap_dispatch (3PCAP)
or
.BR pcap_loop (3PCAP)
to return rather than looping; they will return the number of packets
that have been processed so far, or
.B PCAP_ERROR_BREAK
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(3PCAP), or pcap_next_ex(3PCAP),
a call to pcap_breakloop() in a different thread will not unblock that
thread.
.ft R
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
.BR SetEvent ()
on the result of
.BR pcap_getevent ()
on a
.B pcap_t
on which the thread is blocked on Windows.  Asynchronous procedure calls
will not work on Windows, as a thread blocked on a
.B pcap_t
will not be in an alertable state.
.ft R
.PP
Note that
.BR pcap_next ()
and
.BR pcap_next_ex ()
will, on some platforms, loop reading packets from the OS; that loop
will not necessarily be terminated by a signal, so
.BR pcap_breakloop ()
should be used to terminate packet processing even if
.BR pcap_next ()
or
.BR pcap_next_ex ()
is being used.
.PP
.BR pcap_breakloop ()
does not guarantee that no further packets will be processed by
.BR pcap_dispatch ()
or
.BR pcap_loop ()
after it is called; at most one more packet might be processed.
.PP
If
.B PCAP_ERROR_BREAK
is returned from
.BR 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
.B PCAP_ERROR_BREAK
and clear the flag.
.SH SEE ALSO
.BR pcap (3PCAP)