fblocked(3tcl) Tcl Built-In Commands fblocked(3tcl)
NAME
fblocked - Test whether the last input operation exhausted all avail-
able input
SYNOPSIS
fblocked channelId
DESCRIPTION
The fblocked command returns 1 if the most recent input operation on
channelId returned less information than requested because all avail-
able input was exhausted. For example, if gets is invoked when there
are only three characters available for input and no end-of-line se-
quence, 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 stan-
dard channel (stdin, stdout, or stderr), the return value from an invo-
cation of open or socket, or the result of a channel creation command
provided by a Tcl extension.
EXAMPLE
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 con-
nect {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 in-
coming connections... socket -server connect 12345 vwait forever
SEE ALSO
gets(3tcl), open(3tcl), read(3tcl), socket(3tcl), Tcl_StandardChan-
nels(3tcl)
KEYWORDS
blocking, nonblocking
Tcl 7.5 fblocked(3tcl)
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