1fblocked(n) Tcl Built-In Commands fblocked(n)
2
6 fblocked - Test whether the last input operation exhausted all avail‐
7 able input
8
10 fblocked channelId
11
14 The fblocked command returns 1 if the most recent input operation on
15 channelId returned less information than requested because all avail‐
16 able input was exhausted. For example, if gets is invoked when there
17 are only three characters available for input and no end-of-line se‐
18 quence, gets returns an empty string and a subsequent call to fblocked
19 will return 1.
20 ChannelId must be an identifier for an open channel such as a Tcl stan‐
22 dard channel (stdin, stdout, or stderr), the return value from an invo‐
23 cation of open or socket, or the result of a channel creation command
24 provided by a Tcl extension.
25
27 The fblocked command is particularly useful when writing network
28 servers, as it allows you to write your code in a line-by-line style
29 without preventing the servicing of other connections. This can be
30 seen in this simple echo-service:
31 # This is called whenever a new client connects to the server proc con‐
33 nect {chan host port} {
34 set clientName [format <%s:%d> $host $port]
35 puts "connection from $clientName"
36 fconfigure $chan -blocking 0 -buffering line
37 fileevent $chan readable [list echoLine $chan $clientName] }
38 # This is called whenever either at least one byte of input # data is
40 available, or the channel was closed by the client. proc echoLine
41 {chan clientName} {
42 gets $chan line
43 if {[eof $chan]} {
44 puts "finishing connection from $clientName"
45 close $chan
46 } elseif {![fblocked $chan]} {
47 # Didn't block waiting for end-of-line
48 puts "$clientName - $line"
49 puts $chan $line
50 } }
51 # Create the server socket and enter the event-loop to wait # for in‐
53 coming connections... socket -server connect 12345 vwait forever
54
56 gets(n), open(n), read(n), socket(n), Tcl_StandardChannels(3)
57
59 blocking, nonblocking
60Tcl 7.5 fblocked(n)