Hi !
I think it has been discussed before but I would like to use Semaphores, to allow multiple reads but 1 write at once (which is in fact commons operations in a multi-thread program).

My program must work under OSX/Nux and Windows.
I may have missed something but I can not find something suitable for me.
Under Windows OpenSemaphore, under unixes CurrentTM.Semaphore*...

Is there any TSemaphore class of equivalent ? Or may be an example how to use Semaphores ? :)

I've wondered the same thing.... In the end I had to write code like the following:
Not idea, but it works. We needed to support Linux and Windows only.

procedure TtiPool.CreatePoolSemaphore;
begin
  {$IFDEF MSWINDOWS}
  if FSemaphore  0 then
    CloseHandle(FSemaphore);
  FSemaphore := CreateSemaphore(nil, FMaxPoolSize, FMaxPoolSize, nil);
  {$ENDIF MSWINDOWS}
  {$IFDEF LINUX}
  sem_destroy(FSemaphore);
  if sem_init(FSemaphore, 0, FMaxPoolSize)  0 then
    raise Exception.Create('Failed to create the semaphore');
  {$ENDIF LINUX}
end;

Regards,
- Graeme -

_______________________________________________
fpGUI - a cross-platform Free Pascal GUI toolkit
http://opensoft.homeip.net/fpgui/

Thanks !

I think I can safely change LINUX by UNIX and it should work on OS X too.
I will made a TSemaphore :)

I realize you have already made a TSemaphore like. May be I can directly use it for my purposes ?

CurrentTM.Semaphore* should also work under Windows (if it doesn't, please file a bug report). And the way to use those is by calling

{$ifdef unix}
uses
   cthreads;
{$endif}
var
   p: pointer;
begin
   p:=currenttm.SemaphoreInit;
   currenttm.semaphorepost(p);
   currenttm.semaphorewait(p);
   currenttm.semaphoredestroy(p);
end.

Jonas

No, you can't, because sem_init does not exist on Mac OS X. Use the RTL implementation, it works on all platforms. Further, the above code looks buggy because it always calls sem_destroy for FSemaphore, even it was not allocated (and that may cause the program to crash, depending on the contents of FSemaphore at that point and the implementation of sem_init).

Jonas

sem_* don't came from pthreads ?
Under OS X you can do
{$ifdef unix}
uses
  cthreads;
{$endif}

I thought it would follow the same behavior. But I agree RTL is my friend :)

Jonas_______________________________________________ fpc-pascal maillist - http://lists.freepascal.org/mailman/listinfo/fpc-pascal

I though that too but currenttm can not be found under Windows. What is the good unit for it ?

"The sem_init() function is part of the Semaphores option and need not be available on all implementations"

cthreads is not required to directly call any posix routines. It is
required to call the RTL versions of the thread-related routines;

Jonas

Damien Gerard wrote

I though that too but currenttm can not be found under Windows. What is the good unit for it ?

Indeed, you shouldn't use currenttm. Use this routine instead (from the system unit, the result indicates success or failure):

Function GetThreadManager(Var TM : TThreadManager) : Boolean;

Jonas

Thanks Jonas. :) I didn't know about this. I'll update my old code to the above...

Regards,
- Graeme -

_______________________________________________
fpGUI - a cross-platform Free Pascal GUI toolkit
http://opensoft.homeip.net/fpgui/

Ok thanks ! I ve got all I need to use Semaphore, except one thing : How I set the limit ?
I mean I want to restrict to 4 concurrent accesses to a shared ressource.

With pthread I have
int sem_init(sem_t *sem, int pshared, unsigned int value);
but here we have only
TSempahoreInitHandler     = function: Pointer;

Sorry I have for sure missed something :)

Call SemaphorePost 4 times after initialising it.

Jonas

Oki Thanks !