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.TH PCAP_GET_REQUIRED_SELECT_TIMEOUT 3PCAP "25 July 2018"
.SH NAME
pcap_get_required_select_timeout \- get a file descriptor on which a
select() can be done for a live capture
.SH SYNOPSIS
.nf
.ft B
#include <pcap/pcap.h>
.ft
.LP
.ft B
struct timeval *pcap_get_required_select_timeout(pcap_t *p);
.ft
.fi
.SH DESCRIPTION
.B pcap_get_required_select_timeout()
returns, on UNIX, a pointer to a
.B struct timeval
containing a value that must be used as the minimum timeout in
.BR select(2) ,
.BR poll(2) ,
.BR epoll_wait(2) ,
and
.B kevent()
calls if
.B pcap_get_selectable_fd(3PCAP)
returns
.BR PCAP_ERROR .
.PP
The timeout that should be used in those calls must be no larger than
the smallest of all timeouts returned by
.B \%pcap_get_required_select_timeout()
for devices from which packets will be captured.
.PP
The device for which
.B pcap_get_selectable_fd()
returned
.B PCAP_ERROR
must be put in non-blocking mode with
.BR pcap_setnonblock(3PCAP) ,
and an attempt must always be made to read packets from the device
when the
.BR select() ,
.BR poll() ,
.BR epoll_wait() ,
or
.B kevent()
call returns.
.PP
Note that a device on which a read can be done without blocking may,
on some platforms, not have any packets to read if the packet buffer
timeout has expired.  A call to
.B pcap_dispatch(3PCAP)
or
.B pcap_next_ex(3PCAP)
will return 0 in this case, but will not block.
.PP
.B pcap_get_required_select_timeout()
is not available on Windows.
.SH RETURN VALUE
A pointer to a
.B struct timeval
is returned if the timeout is required; otherwise
.B NULL
is returned.
.SH BACKWARD COMPATIBILITY
This function became available in libpcap release 1.9.0.  In previous
releases,
.BR select() ,
.BR poll() ,
.BR epoll_wait() ,
and
.B kevent()
cannot be used on any capture source for which
.B pcap_get_selectable_fd
returns \-1.
.SH SEE ALSO
pcap(3PCAP), pcap_get_selectable_fd(3PCAP), select(2), poll(2),
epoll_wait(2), kqueue(2)