[Lazarus] Thread safe

[Mattias Gaertner]

On Sun, 31 May 2009 01:50:19 +1000
SteveG <steveg at nevets.com.au> wrote:

> On Saturday 30 May 2009 17:09:41 Mattias Gaertner wrote:
> > On Sat, 30 May 2009 12:55:14 +1000
> >
> > SteveG <steveg at nevets.com.au> wrote:
> > > Would appreciate anybody clearing this up for me -
> > >
> > > If I use a TTimer on a GUI form to call a function, is the
> > > function within the Main thread at all times (therefore gui
> > > threadsafe) ?
> >
> > yes
> >
> > > If the above function then calls a function within a library, is
> > > the call still within the main thread (still safe) ?
> >
> > Yes.
> > Unless the library starts another thread.
> 
> One further assumption (to save a little time) - 
> If a TTimer is created within the 'Initialization' section of the Laz
> app, and the timer event calls a function within a library, all calls
> within that function, and any functions it calls should be thread/gui
> safe ?

The TTimer events are called by the main gui thread.
I don't know if this fits your thread safety definition.

 
> Assuming the above to be true, can you tell me why the following
> 'sometimes' fails (works about 3 of 5 calls)  when used from within
> the library function?
> 
> I pass the address of a WinCtrl (eg Label) to the function, then use
> the following
>   TLabel( CompAddress^ ).Caption := 'test';
> 
> also a problem is 'Application.ProcessMessages' within the library
> 
> These (and variations of) seem to fail regularly, but work fine from
> the Laz app itself

I can't say without knowing the code. Please provide an example.


Mattias