[fpc-pascal] Where is IsMultiThreaded set under Linux?

[Sven Barth]

Am 08.10.2010 13:33, schrieb Graeme Geldenhuys:
> Hi,
>
> Is it the line with InterlockedExchange() call?  The reason I ask, I'm
> using FPC 2.4.3 under 64-bit linux and using fpGUI. All other
> platforms has a clear 'IsMultiThreaded := True' in the RTL code, but
> not for Unix. It seems CheckSynchronized() is never called in
> fpGUI/X11 because IsMultiThread is never True, even though I have
> 'cthreads' unit defined as the first unit in my fpGUI program.
>
>
> -------------[ rtl/unix/cthreads.pp]------------------
> ....
>        { Initialize multithreading if not done }
>        if not IsMultiThread then
>          begin
>            if (InterLockedExchange(longint(IsMultiThread),ord(true)) = 0) then
>              begin
>                { We're still running in single thread mode, setup the TLS }
>                pthread_key_create(@TLSKey,nil);
>                InitThreadVars(@CRelocateThreadvar);
>              end
>          end;
> ....
> -------------------------------
>
>
> In fpGUI, CheckSynchronized is executed as follows in the main event loop.
>
>
> ....
>    if IsMultiThreaded then
>      CheckSynchronized();
> ...
>
>

InterlockExchange does exactly that. It writes "ord(true)" to 
"longint(IsMultiThread)" and returns its old value (0 = ord(false)).

Note: You must start at least one thread (besides the main thread) to 
turn "IsMultiThread" to true.

Btw: the check for IsMultiThread inside of RTL code is a bit dangerous 
as ported Delphi applications might set it manually to true out of old 
habit (which is bad if the multithreading initialization checks that var).

Regards,
Sven