Hello there!

I've written a very simple Tk application that is very serial. Recently I added support for http requests like this:

set token [::http::geturl example.com]
set data [::http::data $token]
(configure .toplevel.mywidget with $data)

I soon discovered that ::http::geturl doesn't block the main loop, which is great, but it happens that for my very serial application, it can be problematic sometimes. For instance: sometimes I destroy the toplevel in which mywidget lives before it got a chance to receive $data, so when geturl resumes its execution, my code throws an error because it tries to configure mywidget.

The easiest solution I thought was to make ::http::geturl blockable, but I couldn't. I tried ::http::wait (with -command), vwait and tkwait, with no success. Yes, guys, making this GUI block would be perfect for me, since I'm the sole user of this small application :-) Can I?

Alternatively, is there a more elegant solution that is not to add a bunch of if's to check if widgets still exist?

Thank you very much and I hope you have a great 2024!

Silas Silva <silasdb@gmail.com> wrote:
> Hello there!
>
> I've written a very simple Tk application that is very serial.
> Recently I added support for http requests like this:
>
> set token [::http::geturl example.com]
> set data [::http::data $token]
> (configure .toplevel.mywidget with $data)
>
> I soon discovered that ::http::geturl doesn't block the main loop,
> which is great, but it happens that for my very serial application,
> it can be problematic sometimes. For instance: sometimes I destroy
> the toplevel in which mywidget lives before it got a chance to
> receive $data, so when geturl resumes its execution, my code throws
> an error because it tries to configure mywidget.
> [...]
> Alternatively, is there a more elegant solution that is not to add a
> bunch of if's to check if widgets still exist?

If it is just a missing toplevel, you could wrap the 'configure' in a
try:

try {
configure .toplevel.mywidget with $data
} on error {a b} {
# do whatever you should do here when the configure fails
}

Or you can check for the toplevel before trying to configure it:

if {[winfo exists .toplevel]} {
configure .toplevel.mywidget with $data
} else {
# do what you need to do when the toplevel has been destroyed
}

Note that the "do whatever" should include freeing the return token
from geturl, otherwise you will have a memory leak.

On Wednesday, January 3, 2024 at 8:45:17 PM UTC-3, Rich wrote:
> If it is just a missing toplevel, you could wrap the 'configure' in a
> try:

Thanks for the answer. That was what I was doing, but I ended up just "freezing" the UI using [tk busy] (suggestion from schelte in the Tcler's Chatroom. Thanks!). Anyway, I'll surround code with [try] or a check as you suggested, specially in places where [tk busy] does not solve my particular problem.

Thank you very much!