Am 08.10.2010 14:03, schrieb Graeme Geldenhuys:
Hi,
On 8 October 2010 13:37, Sven Barth wrote:
Note: You must start at least one thread (besides the main thread) to turn
"IsMultiThread" to true.
I am, and changing my fpGUI code to the following does indeed prove
that you are right. As soon as my thread is started, I see the '*****'
output, but unfortunately only once. Let me explain.
if IsMultiThreaded then
begin
writeln('******');
CheckSynchronized();
end;
What I am trying to debug is that as soon as I call mythread.waitfor,
then WaitFor() blocks the applications main event loop, thus the
application just hangs. This only occurs under X11, not under Windows.
I can work around that problem, by doing the following.... I have to
introduce a boolean variable in my thread class, set it to True at the
end of the thread's Execute method, as follows:
procedure TBarThread.Execute;
begin
FFinished := False; // work-around variable
while not Terminated do
begin
Synchronize(@UpdateProgressBar);
end;
FFinished := True; // work-around variable
end;
....Then use a while loop (instead of WaitFor), to check for that
variable, and if not True, call fpgApplication.ProcessMessages
instead.
procedure TMainForm.ButtonClicked(Sender: TObject);
begin
ProgressBar1.Position := ProgressBar1.Min;
if not Assigned(FThread) then
begin
writeln('program: creating thread...');
FThread := TBarThread.Create(True);
FThread.ProgressBar := ProgressBar1;
end;
writeln('program: starting the thread...');
FThread.Start;
writeln('program: waiting for thread...');
FThread.WaitFor; // Can use this, it blocks the main event loop
// my work-around
while not FThread.Finished do
begin
sleep(100);
fpgApplication.ProcessMessages;
end;
writeln('program: thread is finished!');
Label1.Text := 'Thread is done';
FreeAndNil(FThread);
end;
Obviously this is a hack, and damn ugly. I shouldn't need to do this.
But still I haven't figured out why the application's main event loop
is blocked by WaitFor.
Writing a console app, that does use a thread to count down from 20 to
0, I can use a WaitFor, and it works (even under Linux). So clearly
there is a problem in fpGUI, and more specifically in the X11 support
code. Unbelievable that I haven't picked up on this sooner.... then
again, I have never had a need for WaitFor usage until now. :-/
1. If you do a WaitFor the calling thread will be suspended until the
thread you called WaitFor on terminates (or the timeout elapses, but our
WaitFor doesn't have a timeout parameter...). Thus it is normal that
your main loop appears to hang.
2. Does your thread really terminate till then? Did you test a thread
that does nothing and terminates immediatly?
I can't help you much with X11, cause I've not yet found the time and
the need to dig into it.
Regards,
Sven
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