'\" '\" Copyright (c) 1996 Sun Microsystems, Inc. '\" '\" See the file "license.terms" for information on usage and redistribution '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. '\" .TH fblocked n 7.5 Tcl "Tcl Built-In Commands" .BS '\" Note: do not modify the .SH NAME line immediately below! .SH NAME fblocked \- Test whether the last input operation exhausted all available input .SH SYNOPSIS \fBfblocked \fIchannelId\fR .BE .SH DESCRIPTION .PP The \fBfblocked\fR command returns 1 if the most recent input operation on \fIchannelId\fR returned less information than requested because all available input was exhausted. For example, if \fBgets\fR is invoked when there are only three characters available for input and no end-of-line sequence, \fBgets\fR returns an empty string and a subsequent call to \fBfblocked\fR will return 1. .PP \fIChannelId\fR must be an identifier for an open channel such as a Tcl standard channel (\fBstdin\fR, \fBstdout\fR, or \fBstderr\fR), the return value from an invocation of \fBopen\fR or \fBsocket\fR, or the result of a channel creation command provided by a Tcl extension. .SH EXAMPLE The \fBfblocked\fR 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: .PP .CS # 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 {![\fBfblocked\fR $chan]} { # Didn't block waiting for end-of-line puts "$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 .CE .SH "SEE ALSO" gets(n), open(n), read(n), socket(n), Tcl_StandardChannels(3) .SH KEYWORDS blocking, nonblocking