[Lazarus] animated splash screen for lengthy operation, works with windows, doesn't with linux

Michael Van Canneyt michael at freepascal.org
Mon Mar 27 16:50:45 CEST 2023

On Mon, 27 Mar 2023, Luca Olivetti via lazarus wrote:

> El 27/3/23 a les 16:13, Michael Van Canneyt via lazarus ha escrit:
>> On Mon, 27 Mar 2023, Luca Olivetti via lazarus wrote:
>>> El 27/3/23 a les 11:59, Luca Olivetti via lazarus ha escrit:
>>>> [*] instead of opening the query I spawn a thread that opens it, wait 
>>>> for it to finish while executing Application.ProcessMessages and 
>>>> eventually reraise the exception that was generated inside the thread.
>>> Speaking of which, I encapsulated it in a procedure (TWaitForm is the 
>>> spash screen, Aproc is a procedure of object, TExecInThread simply 
>>> calls AProc in its execute method):
>>> procedure ExecWithSplash(AProc:TThreadProc);
>>> var wf:TWaitForm;
>>>    ut:TExecInThread;
>>> begin
>>>  Wf:=TWaitForm.Create(Application);
>>>  WF.Show;
>>>  ut:=TExecInThread.create(AProc);
>>>  while not ut.Finished
>>>    Application.ProcessMessages
>>>  wf.free;
>>>  if ut.FatalException<>nil then
>>>    raise(ut.FatalException);
>>>  ut.free;
>> Ehm. In case of an exception, ut will never be freed ?
> That's what I said.
> I was looking for a way to free it *and* raise the exception in the 
> context of the main thread.
> If I move the ut.free before the raise, the exception has already been 
> freed and it's invalid, causing a sigsev, if I enclose it in a 
> try..finally the exception handler will be called after the finally has 
> freed the thread (and the exception, so it's the same problem).

Normally, I'd do

Raise Exception(ut.fatalexception.classtype).Create(ut.fatalexception.message);


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