[Solved] Indivisibly saving a handler address

[MarkMLl]

Is it possible to indivisibly save the address of a procedure, something like the commented-out lines in

Code: Pascal  [Select][+][-]

1. procedure TBeepDemoForm.ButtonStdoutBeepClick(Sender: TObject);
2.  
3. var
4.   savedBeep: TBeepHandler= @doStdoutBeep;
5.  
6. begin
7. //  savedBeep := InterlockedExchange(OnBeep, PtrUInt(savedBeep));
8.  
9.   savedBeep := OnBeep;
10.   OnBeep := @doStdoutBeep;
11.   Application.ProcessMessages;
12.   Beep();
13.   Application.ProcessMessages;
14.   OnBeep := savedBeep;
15.  
16. //  savedBeep := InterlockedExchange(OnBeep, PtrUInt(savedBeep))
17. end;
18.  

At present I am getting

Code: [Select]

beepdemocode.pas(193,42) Error: Call by var for arg no. 1 has to match exactly: Got "<procedure variable type of procedure;Register>" expected "LongWord"

with no significant improvement if I introduce @ etc. on the first parameter.

MarkMLl

[ASerge]

Is it possible to indivisibly save the address of a procedure, something like the commented-out lines in

Like this?

Code: Pascal  [Select][+][-]

1. {$APPTYPE CONSOLE}
2.  
3. procedure PProc;
4. begin
5.   Writeln('P');
6. end;
7.  
8. procedure QProc;
9. begin
10.   Writeln('Q');
11. end;
12.  
13. var
14.   P, Q: TProcedure;
15. begin
16.   P := @PProc;
17.   Q := @QProc;
18.   InterlockedExchange(Pointer(P), Pointer(Q));
19.   P; // Write Q
20.   Readln;
21. end.

[Thaddy]

Or the volatile intrinsic but that is only in trunk.
https://wiki.freepascal.org/FPC_New_Features_Trunk#Support_for_.22volatile.22_intrinsic

[MarkMLl]

Is it possible to indivisibly save the address of a procedure, something like the commented-out lines in

Like this?

I'm not sure whether that helps, with OnBeep being predefined and potentially accessible to other parts of the system.

I'm not necessarily saying that I'm worried about the thread-safety of this, but I've got this gut feeling that the more that can be done to stop that procedure address being handled as two 32-bits rather than a single 64-bit.

MarkMLl

[MarkMLl]

Or the volatile intrinsic but that is only in trunk.
https://wiki.freepascal.org/FPC_New_Features_Trunk#Support_for_.22volatile.22_intrinsic

Thanks for that but in the interest of keeping a test program usable on older systems I'll probably give it a miss.

MarkMLl

[MarkMLl]

Fixed it. The major thing I was doing wrong was not using the special 64-bit variant of the exchange function: inexcusable in light of my criticism of Pascal's sloppy conversions. Hence with a bit of tidying up:

Code: Pascal  [Select][+][-]

1. function InterlockedExchangeBH(var target: TBeepHandler; const source: TBeepHandler): TBeepHandler; inline;
2.  
3. begin
4. {$if sizeof(TBeepHandler) = 8 }
5.   result := TBeepHandler(InterlockedExchange64(PtrUInt(target), PtrUInt(source)))
6. {$else                        }
7.   result := TBeepHandler(InterlockedExchange(PtrUInt(target), PtrUInt(source)))
8. {$endif                       }
9. end;
10.  
11.  
12. procedure TBeepDemoForm.ButtonStdoutBeepClick(Sender: TObject);
13.  
14. var
15.   savedBeep: TBeepHandler = @doStdoutBeep;
16.  
17. begin
18.   savedBeep := InterlockedExchangeBH(OnBeep, savedBeep);
19.   Application.ProcessMessages;
20.   Beep();
21.   Application.ProcessMessages;
22.   InterlockedExchangeBH(OnBeep, savedBeep)
23. end;
24.  

MarkMLl

[Thaddy]

That is a bit over the top or a bug that you have to do that, since InterlockedExchange has an overload for pointers, i.e,. independent of pointer size.
https://www.freepascal.org/docs-html/rtl/system/interlockedexchange.html

[MarkMLl]

That is a bit over the top or a bug that you have to do that, since InterlockedExchange has an overload for pointers, i.e,. independent of pointer size.
https://www.freepascal.org/docs-html/rtl/system/interlockedexchange.html

Yes, I'd been referring to that. But the code shown was the only combination I could get working.

MarkMLl

[ASerge]

Yes, I'd been referring to that. But the code shown was the only combination I could get working.

And what is the difference from the example that I gave earlier?

[MarkMLl]

And what is the difference from the example that I gave earlier?

The fact that mine works with a predefined variable outside my control.

MarkMLl

[ASerge]

The fact that mine works with a predefined variable outside my control.

I still don't understand. If you had made a short example, it might have been clearer.