fblocked(3tcl)               Tcl Built-In Commands              fblocked(3tcl)

       fblocked - Test whether the last input operation exhausted all
       available input

       fblocked channelId

       The fblocked command returns 1 if the most recent input operation on
       channelId returned less information than requested because all
       available input was exhausted.  For example, if gets is invoked when
       there are only three characters available for input and no end-of-line
       sequence, gets returns an empty string and a subsequent call to
       fblocked will return 1.

       ChannelId must be an identifier for an open channel such as a Tcl
       standard channel (stdin, stdout, or stderr), the return value from an
       invocation of open or socket, or the result of a channel creation
       command provided by a Tcl extension.

       The fblocked command is particularly useful when writing network
       servers, as it allows you to write your code in a line-by-line style
       without preventing the servicing of other connections.  This can be
       seen in this simple echo-service:

       # This is called whenever a new client connects to the server proc
       connect {chan host port} {
           set clientName [format <%s:%d> $host $port]
           puts "connection from $clientName"
           fconfigure $chan -blocking 0 -buffering line
           fileevent $chan readable [list echoLine $chan $clientName] }

       # This is called whenever either at least one byte of input # data is
       available, or the channel was closed by the client.  proc echoLine
       {chan clientName} {
           gets $chan line
           if {[eof $chan]} {
               puts "finishing connection from $clientName"
               close $chan
           } elseif {![fblocked $chan]} {
               # Didn't block waiting for end-of-line
               puts "$clientName - $line"
               puts $chan $line
           } }

       # Create the server socket and enter the event-loop to wait # for
       incoming connections...  socket -server connect 12345 vwait forever

       gets(3tcl), open(3tcl), read(3tcl), socket(3tcl),

       blocking, nonblocking

Tcl                                   7.5                       fblocked(3tcl)