NAME¶
fblocked - Test whether the last input operation exhausted all available 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
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.
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 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
SEE ALSO¶
gets(3tcl), open(3tcl), read(3tcl), socket(3tcl), Tcl_StandardChannels(3tcl)
KEYWORDS¶
blocking, nonblocking