[Lazarus] Mutlithreaded Dll Callback crashes my Application

[Sven Barth]

On 25.08.2010 21:33, José Mejuto wrote:
> Hello Lazarus-List,
>
> Wednesday, August 25, 2010, 8:47:23 PM, you wrote:
>
> SB>  IsMultiThread is only a variable. Setting it is only useful recognized
> SB>  once FPC threading code is called. So instead of setting IsMultiThread
> SB>  to true you must create at least one thread in FPC (it can be a dummy
> SB>  thread that immediately terminates).
>
> In Delphi setting IsMultithread to true is a must to use non TThread
> threads. Taken from Embarcadero QA:
>

FPC is not Delphi and in this regard those two differ. The method 
SysInitMultiThreading in rtl/win/systhrd.pas which initializes the 
thread local storage is only called on two locations:
- when a new thread is created using FPC routines (BeginThread, TThread)
- when the unit system is initalized (using InitSystemThreads) AND if 
the application is a library

If you don't create a thread the thread local storage won't be 
initialized and thus threadvars won't work and thus the heap will not 
work correctly.

> Also the one thread creation is only for Unix systems, win32 does not
> have this problem since a lot of time.

Windows DOES have this problem.

>
> On the other hand, if Unix needs one thread creation then it should be
> automagically done in the initialization section of cthreads, do not ?
>

This might indeed be a solution.

Regards,
Sven