fblocked(n) Tcl Built-In Commands fblocked(n)


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 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 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 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 $chan]} { # Didnt block waiting for end-of-line puts "$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(n), open(n), read(n), socket(n), Tcl_StandardChannels(3)

KEYWORDS blocking, nonblocking

Tcl 7.5 fblocked(n)