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  20 .TH PCAP_SETNONBLOCK 3PCAP "25 July 2018"
  21 .SH NAME
  22 pcap_setnonblock, pcap_getnonblock \- set or get the state of
  23 non-blocking mode on a capture device
  24 .SH SYNOPSIS
  25 .nf
  26 .ft B
  27 #include <pcap/pcap.h>
  28 .ft
  29 .LP
  30 .nf
  31 .ft B
  32 char errbuf[PCAP_ERRBUF_SIZE];
  33 .ft
  34 .LP
  35 .ft B
  36 int pcap_setnonblock(pcap_t *p, int nonblock, char *errbuf);
  37 int pcap_getnonblock(pcap_t *p, char *errbuf);
  38 .ft
  39 .fi
  40 .SH DESCRIPTION
  41 .BR pcap_setnonblock ()
  42 puts a capture handle into ``non-blocking'' mode, or takes it out
  43 of ``non-blocking'' mode, depending on whether the
  44 .I nonblock
  45 argument is non-zero or zero.  It has no effect on ``savefiles''.
  46 If there is an error,
  47 .B PCAP_ERROR
  48 is returned and
  49 .I errbuf
  50 is filled in with an appropriate error message; otherwise, 0 is
  51 returned.
  52 .PP
  53 In
  54 ``non-blocking'' mode, an attempt to read from the capture descriptor
  55 with
  56 .BR pcap_dispatch (3PCAP)
  57 and
  58 .BR pcap_next_ex (3PCAP)
  59 will, if no packets are currently available to be read, return 0
  60 immediately rather than blocking waiting for packets to arrive.
  61 .PP
  62 .BR pcap_loop (3PCAP)
  63 will loop forever, consuming CPU time when no packets are currently
  64 available;
  65 .BR pacp_dispatch ()
  66 should be used instead.
  67 .BR pcap_next (3PCAP)
  68 will return NULL if there are no packets currently available to read;
  69 this is indistinguishable from an error, so
  70 .BR pcap_next_ex ()
  71 should be used instead.
  72 .PP
  73 When first activated with
  74 .BR pcap_activate (3PCAP)
  75 or opened with
  76 .BR pcap_open_live (3PCAP) ,
  77 a capture handle is not in ``non-blocking mode''; a call to
  78 .BR pcap_setnonblock ()
  79 is required in order to put it into ``non-blocking'' mode.
  80 .SH RETURN VALUE
  81 .BR pcap_getnonblock ()
  82 returns the current ``non-blocking'' state of the capture descriptor; it
  83 always returns 0 on ``savefiles''.
  84 If there is an error,
  85 .B PCAP_ERROR
  86 is returned and
  87 .I errbuf
  88 is filled in with an appropriate error message.
  89 .PP
  90 .I errbuf
  91 is assumed to be able to hold at least
  92 .B PCAP_ERRBUF_SIZE
  93 chars.
  94 .SH SEE ALSO
  95 .BR pcap (3PCAP),
  96 .BR pcap_next_ex (3PCAP),
  97 .BR pcap_geterr (3PCAP)