Tcl - detecting network connection and tcludp

Author

detecting network connection and tcludp

shamil

2005-10-23, 7:56 am

Hello,

I'm trying to use tcludp to send data and also trying to detect when
network connection is lost by periodically checking for variable
"connect" and re-setting it. If its value is 1, network connection
exists, otherwise it got lost or the plug was pulled. A small message
on a label should indicate if data is being sent or not. In case no
connection, I'm looping every second closing previous socket, opening a
new one, do fconfigure, and fileevent (all this in proc
startBroadcast).

However, in the proc loop below, the line:

puts -nonewline $sock {whatever I want to send...}

for some reason is not invoking proc receiveBroadcast! Which should be
invoked every time data is put into the socket (as defined by the
fileevent). Could it be I didn't properly define my fileevent? Or what
could it be? Any help would be greatly appreciated.

Shamil

#--------------- Begin Script ----------------#
package require udp

pack [label .l -text {display status}]

#############################
proc startBroadcast {} {

variable connected
variable address 224.1.1.1
variable port 1234
variable sock

catch {close $sock} ;# close previous socket, if exists. This is to
;# prevent from crashing while trying again to
;# connect again

set sock [udp_open $port]

if {[catch {fconfigure $sock -blocking 0 -buffering none -translation
binary -mcastadd $address -remote [list $address $port]}]} {
set connected 0
puts "fconfigure failed"
.l configure -text "Lost connection. Current time is \
[clock format [clock seconds] -format %r]"

} else {set connected 1
puts "fconfigure passed"}

fileevent $sock readable receiveBroadcast
}

##############################
proc receiveBroadcast {} {

variable sock
variable connected

puts "received data: [read $sock]"
set connected 1
..l configure -text "Sending...[clock format [clock seconds] -format
%r]"
return
}

##############################
proc loop {} {
variable connected
variable sock

set connected 0
puts -nonewline $sock {whatever I want to send...}

;# at this point, I would've thought "connected" = 1 as long as
;# network connection exists because it would be set from the
;# receiveBroadcast procedure. But this is not the case. WHY??

if {!$connected} {startBroadcast} ;# if no connection, try again

after 1000 loop
}
#############################

startBroadcast
loop
#--------------- End Script ----------------#

Gerald W. Lester

2005-10-23, 7:56 am

I do not believe the receive fileevent will fire for things you yourself
send out on the port.

shamil wrote:
> Hello,
>
> I'm trying to use tcludp to send data and also trying to detect when
> network connection is lost by periodically checking for variable
> "connect" and re-setting it. If its value is 1, network connection
> exists, otherwise it got lost or the plug was pulled. A small message
> on a label should indicate if data is being sent or not. In case no
> connection, I'm looping every second closing previous socket, opening a
> new one, do fconfigure, and fileevent (all this in proc
> startBroadcast).
>
> However, in the proc loop below, the line:
>
> puts -nonewline $sock {whatever I want to send...}
>
> for some reason is not invoking proc receiveBroadcast! Which should be
> invoked every time data is put into the socket (as defined by the
> fileevent). Could it be I didn't properly define my fileevent? Or what
> could it be? Any help would be greatly appreciated.
>
> Shamil
>
>
>
> #--------------- Begin Script ----------------#
> package require udp
>
> pack [label .l -text {display status}]
>
> #############################
> proc startBroadcast {} {
>
> variable connected
> variable address 224.1.1.1
> variable port 1234
> variable sock
>
> catch {close $sock} ;# close previous socket, if exists. This is to
> ;# prevent from crashing while trying again to
> ;# connect again
>
> set sock [udp_open $port]
>
> if {[catch {fconfigure $sock -blocking 0 -buffering none -translation
> binary -mcastadd $address -remote [list $address $port]}]} {
> set connected 0
> puts "fconfigure failed"
> .l configure -text "Lost connection. Current time is \
> [clock format [clock seconds] -format %r]"
>
> } else {set connected 1
> puts "fconfigure passed"}
>
> fileevent $sock readable receiveBroadcast
> }
>
> ##############################
> proc receiveBroadcast {} {
>
> variable sock
> variable connected
>
> puts "received data: [read $sock]"
> set connected 1
> .l configure -text "Sending...[clock format [clock seconds] -format
> %r]"
> return
> }
>
> ##############################
> proc loop {} {
> variable connected
> variable sock
>
> set connected 0
> puts -nonewline $sock {whatever I want to send...}
>
> ;# at this point, I would've thought "connected" = 1 as long as
> ;# network connection exists because it would be set from the
> ;# receiveBroadcast procedure. But this is not the case. WHY??
>
> if {!$connected} {startBroadcast} ;# if no connection, try again
>
> after 1000 loop
> }
> #############################
>
> startBroadcast
> loop
> #--------------- End Script ----------------#
>

--
+--------------------------------+---------------------------------------+
| Gerald W. Lester |
|"The man who fights for his ideals is the man who is alive." - Cervantes|
+------------------------------------------------------------------------+

shamil

2005-10-23, 6:59 pm

I'm affraid I don't understand... what other options do I have in
sending data through a socket?

Bruce

2005-10-23, 9:57 pm

shamil wrote:
> I'm affraid I don't understand... what other options do I have in
> sending data through a socket?
>
you misunderstand the response.

you are correctly sending data through the socket.
but a readable fileevent is used for *reading* data from a socket.

to keep your flag current, check the return code from your puts
statement and see if it fails. If it succeeds you are connected.

if you have a slow link and/or sending so much that buffers can
get full and cause unnecessary blocking, then you can use a writable
fileevent to notify you when the socket is available for writing.

Bruce

shamil

2005-10-25, 9:57 pm

Thank you Gerald and Bruce.

My problem was that I was incorrectly expecting my variable "connected"
to be instantly updated from proc receiveBroadcast upon invoking "puts
-nonewline $sock..." from proc loop. This case proved true even when
the data I was sending was very small

I suppose one should not expect the fileevent handler to fire up the
very moment data is put into a socket.

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