[Lazarus] PostMessage return value

Michael Schnell mschnell at lumino.de
Mon Sep 15 16:30:49 CEST 2014

On 09/15/2014 03:57 PM, Xiangrong Fang wrote:
> 2014-09-15 21:44 GMT+08:00 Michael Schnell <mschnell at lumino.de 
> <mailto:mschnell at lumino.de>>:
>     Performance wise it's better not to destroy and create your
>     threads but to manage a thread pool and assign work to the threads
>     as appropriate.
>     Here you would have the threads wait for work  e.g. by trapping
>     themselves in a TCriticalSection for each one.
>     Now the Main thread can easily free a thread after it assigned
>     work to it (e.g. by providing a callback function that is to be
>     called in TThread.Execute). If work is done, the Thread could
>     notify the manager (in the main thread) by
>     Application.QueueAsyncCall or TThread.Queue. TThread. Synchronize
>     would not harm in this case either, as the thread at that time has
>     nothing to do anyway.
> That's exactly what I planed to do. But I don't know 
> "CriticalSections" can be used in here.
Why not (of course there might be alternatives).
>  My original thinking is that, by the end of Execute, I call either 
> PostMessage or QueueAsyncCall to notify main thread that the current 
> thread finished its work.
OK. Moreover TThread.Queue and TThread.Synchronize will work.
> The main thread, in its message handler
(This is the procedure given in Application.QueueAsyncCall, 
TThread.Queue and TThread.Synchronize)
> then know from a status variable that this thread is in suspended status,
OK, suspend will work similar to TCrtiticalSection. But for me Suspend 
is a bit suspicious, as there is no direct Linux and Information-Science 
equivalent to same (while TCriticalSection directly maps to a Semaphore).
> then assign a new work to it and call its Execute() method again.
I don't know how to " call its Execute()". I feel that you can't leave 
the Execute procedures without killing the thread. So you need to call 
the work-procedure from the execute procedure.
> Is that ok? To be exact, when a thread's execute() finished, it will 
> go to a "sleep" status,
No. It will die.
> and can be reused by calling execute() again, right?

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