How do I reliably wait on a thread that has just been created?
delphi, delphi-xe3
Solution
You can call it a bug or a `TThread` design flaw, the problem was discussed many times. See for example http://sergworks.wordpress.com/2011/06/25/sleep-sort-and-tthread-corner-case/
The problem is that if `TThread.Terminated` flag is set too early `TThread.Execute` method is never called. So in your case just don't call `TThread.Terminate` before `TThread.WaitFor`.
Problem
Consider the following program: ``` program TThreadBug; {$APPTYPE CONSOLE} uses SysUtils, Classes, Windows; type TMyThread = class(TThread) protected procedure Execute; override; end; procedure TMyThread.Execute; var i: Integer; begin for i := 1 to 5 do begin Writeln(i); Sleep(100); end; end; procedure UseTThread; var Thread: TMyThread; begin Writeln('TThread'); Thread := TMyThread.Create; Thread.Terminate; Thread.WaitFor; Thread.Free; Writeln('Finished'); Writeln; end; procedure UseTThreadWithSleep; var Thread: TMyThread; begin Writeln('TThreadWithSleep'); Thread := TMyThread.Create; Sleep(100); Thread.Terminate; Thread.WaitFor; Thread.Free; Writeln('Finished'); Writeln; end; begin UseTThread; UseTThreadWithSleep; Readln; end. ``` The output is: ``` TThread Finished TThreadWithSleep 1 2 3 4 5 Finished ``` So it seems that, for some reason, the main thread has to wait some arbitrary amount of time before terminating and waiting for the worker thread. Am I right in thinking that this is a bug in `TThread`? Is there any way I can work around this? I expect that if I get my thread to signal that it has started (using an event), then that would work around the issue. But that makes me feel dirty.