terminal text not displayed in tcltk window real time - window

Question

I am comfortable with tcl but newbie with tk.
I want to display some texts on a window and after several search I found here an example that seem good for me.
My issue is that the display is not put in real time but only when the program end.
Here is the main lines of my program.
Main_program.tcl
#!/bin/sh
# -*- tcl -*-
# The next line is executed by /bin/sh, but not tcl \
exec /usr/local/Cellar/tcl-tk/bin/tclsh "$0" "$#"
set DEBUG 1
source ./GUI_mgt.tcl
source ./utils.tcl
for {set i 0} {$i<500} {incr i} {
after 10
debug_puts $i
}
utils.tcl
proc debug_puts {message} {
if {$::DEBUG} { writeToLog $message }
}
GUI_mgt.tcl
package require Tk
grid [text .log -state disabled -width 80 -height 24 -wrap none]
proc writeToLog {msg} {
set numlines [lindex [split [.log index "end - 1 line"] "."] 0]
.log configure -state normal
if {$numlines==24} {.log delete 1.0 2.0}
if {[.log index "end-1c"]!="1.0"} {.log insert end "\n"}
.log insert end "$msg"
.log configure -state disabled
}
Question: what is wrong or missed in this code ?
Do you know some package or example I can use to display sentences on a separate window ?
Note: I use tcl tk 8.6.6 on macOS Sierra 10.12.5

Answer 1

Your test program is not written in an event driven fashion, so the problems with updating the screen are exacerbated.
The after 10 statement will hang the program and not allow the event loop to be reentered. For purposes of testing only, try:
set ::w10 0
after 10 [list set ::w10 1]
vwait ::w10
instead of the after 10 command. Use of the vwait command is not normally recommended, as nested vwait's will not work as expected.
When you have a very busy loop, the Tk program may never have a chance to re-enter its event loop, and the display is never updated.
The simplest solution is to put an
update
statement at the end of the writeToLog procedure. This is not always the best way to handle this type of issue, but it works.
It will also slow down your loop, as the window must be redrawn each time a log message is written.
Another method would be to put the calculation process into a separate thread or process and send the status updates to the main GUI process.

Answer 2

Ok, so for those of you who use the "update" command or "update idletasks" command, you may have noticed that your GUI or Text Widget will freeze, if you try and move the GUI around on the screen with your mouse, or even try to maximize or resize it. This is a side effect of using this command. It causes an "external event". Which causes the GUI to freeze, or to display "Not responding".
Enter the following two lines of code in place of "update idletasks" and you will not have this freezing issue:
after 500 {set go_on yes}
vwait go_on

Answer 3

I had the same issue with a few different TCL scripts. All we were looking for was a bare bone basic Text window, to display all of our "puts" messages in real-time in the log window, or in a TK text widget.
As Brad mentioned, I found the simplest solution was to use the "update" command. I used the command "update idletasks" and it works perfectly for both "puts" or "insert" commands for your text widget.
Here is my example using a basic TK text widget.
I used two separate procs. One to create the Text logging window, and the second for printing a desired message throughout the script.
The result is real-time logging, WHILE your TCL script is running...and not all displayed at once when your script completes. THANK GOD!!! It was so frustrating trying to track down how to do this. Finally I learned about the "update" command. :P
proc REALTIME_TEXT_LOGGING {} {
# Creates a text widget
text .t -yscrollcommand ".scroll set" -setgrid true -width 40 -height 10 -wrap word
scrollbar .scroll -command ".t yview"
pack .scroll -side right -fill y
pack .t -expand yes -fill both
# Set up the tags
.t tag configure big -font {-family helvetica -size 24 -weight bold}
.t tag configure color1 -foreground red
.t tag configure sunken -relief sunken -borderwidth 1
#Button to activate the display of messages
button .b -text "PRINT MESSAGES TO THE LOG" \
-command {
Insert_Text "HELLO EVERYONE!! This is MSG #1"
after 5000
Insert_Text "HELLO EVERYONE!! This is MSG #2"
after 5000
Insert_Text "HELLO EVERYONE!! This is MSG #3"
after 5000
Insert_Text "HELLO EVERYONE!! This is MSG #4"
after 5000
Insert_Text "HELLO EVERYONE!! This is MSG #5"
}
.t window create end -window .b
}
proc Insert_Text {message} {
# Insert text that has the property of the tags from your TK text widget.
# I also used the "puts" command here, to show printing to the default TCL logging window.
.t insert end "$message\n"
puts "$message\n"
update idletasks
}