[Lazarus] GTK2 threading

Anton Kavalenka anton.k at tut.by
Fri Jan 25 12:21:00 CET 2013

On 23.01.2013 11:44, Michael Schnell wrote:
> On 01/22/2013 06:52 PM, Anton Kavalenka wrote:
>> But GTK Widgetset uses pure Xlib calls for determining keyboard states.
>> Xlib thread-safety is not initialized in GTK2 widgetset.
> AFAIK: As the GUI and Event-queue  related LCL classes (i.e. 
> TApplication) are not thread save themselves (e.g. using global 
> variables). It does not make sense to attach to the System's Widget 
> set in a thread safe way.
> To allow for multiple GUI threads a major update of the appropriate 
> LCL functions would be necessary, so that multiple threads can create 
> their own dedicated TApplication instances.
> -Michael
Dear Michael!

The problem is in LCL implementation itself, not in event queuing.

Real life example:

Off-screen composing is made into TBitmap.
Screen update is made via Synchronize() call or sending a message to the 
control (it does not matter).
This approach works both in Win32/64 and Carbon.

But in LCL-GTK:
Getting and setting bitmap data invoke GTK and Xlib calls.
If it were pure GTK - all would be OK.
GTK is thread-safe and uses mutexes internally.

X is also thread-safe (as soon XInitThreads called).
But currently LCL-GTK is a mix of Xlib and GTK calls, and threading for 
XLib is NOT initialized.

The described example works until i click the form.
This beaks X-message flow.
GTK does not block Xlib and vice versa.

As I have already written, I'll try to provide the "example" of problem,
which works in Win32,Carbon but fails in GTK.


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