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Test Your Knowledge in Computers #108
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The outer layers of the Linux architecture has the shell, shell commands and application programs.
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fblocked(1T)						       Tcl Built-In Commands						      fblocked(1T)


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 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 Tcl 7.5 fblocked(1T)

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