fblocked(1T) Tcl Built-In Commands fblocked(1T)
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NAME
fblocked - Test whether the last input operation exhausted all available input
SYNOPSIS
fblocked channelId
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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 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 with-
out 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(1T), open(1T), read(1T), socket(1T), Tcl_StandardChannels(3TCL)
KEYWORDS
blocking, nonblocking
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Availability | SUNWTcl |
+--------------------+-----------------+
|Interface Stability | Uncommitted |
+--------------------+-----------------+
NOTES
Source for Tcl is available on http://opensolaris.org.
Tcl 7.5 fblocked(1T)