distrib/share/tcl/help/tcl/files/fblocked

   1 NAME
   2        fblocked  -  Test whether the last input operation exhausted all avail-
   3        able input
   4
   5 SYNOPSIS
   6        fblocked channelId
   7
   8
   9 DESCRIPTION
  10        The fblocked command returns 1 if the most recent  input  operation  on
  11        channelId  returned  less information than requested because all avail-
  12        able input was exhausted.  For example, if gets is invoked  when  there
  13        are  only  three  characters  available  for  input  and no end-of-line
  14        sequence, gets returns  an  empty  string  and  a  subsequent  call  to
  15        fblocked will return 1.
  16
  17        ChannelId must be an identifier for an open channel such as a Tcl stan-
  18        dard channel (stdin, stdout, or stderr), the return value from an invo-
  19        cation  of  open or socket, or the result of a channel creation command
  20        provided by a Tcl extension.
  21
  22 EXAMPLE
  23        The fblocked  command  is  particularly  useful  when  writing  network
  24        servers,  as  it  allows you to write your code in a line-by-line style
  25        without preventing the servicing of other  connections.   This  can  be
  26        seen in this simple echo-service:
  27
  28               # This is called whenever a new client connects to the server
  29               proc connect {chan host port} {
  30                   set clientName [format <%s:%d> $host $port]
  31                   puts "connection from $clientName"
  32                   fconfigure $chan -blocking 0 -buffering line
  33                   fileevent $chan readable [list echoLine $chan $clientName]
  34               }
  35
  36               # This is called whenever either at least one byte of input
  37               # data is available, or the channel was closed by the client.
  38               proc echoLine {chan clientName} {
  39                   gets $chan line
  40                   if {[eof $chan]} {
  41                       puts "finishing connection from $clientName"
  42                       close $chan
  43                   } elseif {![fblocked $chan]} {
  44                       # Didn't block waiting for end-of-line
  45                       puts "$clientName - $line"
  46                       puts $chan $line
  47                   }
  48               }
  49
  50               # Create the server socket and enter the event-loop to wait
  51               # for incoming connections...
  52               socket -server connect 12345
  53               vwait forever
  54
  55
  56 SEE ALSO
  57        gets(n), open(n), read(n), socket(n), Tcl_StandardChannels(3)
  58
  59
  60 KEYWORDS