Re: Still confused on new thread starting idle functions to update UI.

[David Buchan <pdbuchan yahoo com>]

On 4 December 2013 13:31,  <jcupitt gmail com> wrote:
> Here's a tiny, complete program that does almost what you want. It's
> gtk2, but should work fine with gtk3.
>
> http://pastebin.com/PsG2UDkY
>
> It just updates a status bar, but it'd be easy to make it do a textview instead.
>
> John

===========================

Hi John,

Thanks for this example. It does appear to be what I want to do. I'll play with it tonight. 
It seems to be precisely what I want to do.

The constraints within which I must work are:

A thread (not main iteration) does stuff that generates messages which need to be periodically added to a 
textview in the UI - sometimes quickly.

I need to use an idle function to update the UI, so the thread calls g_idle_add().

Function g_idle_add() only accepts a *single* pointer as data for the idle function. 

The idle function needs a pointer to the textview I want messages to appear in.

Passing both a pointer to the textview *and* a message requires packing both into a struct.

I want the idle function to have its own copy of the message in memory so that the next message can be 
prepared in the thread without damaging the message the latest idle function is currently posting to the 
textview. srtrdup() seems to be the ticket.

I need then, to use strdup() and still have a pointer to the struct as argument to g_idle_add().

To demonstrate this passing of data, I had created the example I gave. It seems to work fine and Valgrind 
reports no read/write violations or memory leaks.
-------

Things I've learned yesterday are:

1. strdup() (I've never seen or used it before)
2. what the heck heap and stack mean (still more to learn there)
3. a more general and flexible solution is probably to use asynchronous message queuing

and today you have shown me, not only g_new() (never seen that one before), but also a working example. 
Awesome!

Two questions though:

I assume these would be roughly equivalent:

msg = g_new (Msg, 1);

versus

msg = (Msg *) malloc (1 * sizeof (Msg));

The GTK+ documentation:

http://www.gtk.org/api/2.6/glib/glib-Memory-Allocation.html#g-new

...doesn't explicitly say it allocates on the heap, but I see you free it in the idle function that updates 
the UI, so it must be so. i.e., g_new() must use malloc() and not alloca().

Second, why use the sleep (1), or is that just so we can see things happen? i.e., so the whole show isn't 
over in a millisecond?

Thanks for everybody's help and advice.

Dave