Hello,

I have been browsing the web somewhat to figure out how I can have access to a cmpxchg function in freepascal. At the momente I found very little information. Some references on people arguing that this is unnecessary. Others that it takes too much time etcetera. In any case: I _really_ want to have access to a cmpxchg function and tried to find information on the assembler routines on how to get access to such function.

I got as far as the following statement, which doesn't compile of course

function cmpxchg(CompareVal, NewVal: Cardinal; var Target: Cardinal):
Cardinal; assembler;
asm
 lock cmpxchg [%eax], %ecx
end;

Now, the problem is twofold:
1. in which registers are the incoming values ?
2. there are syntax errors in this couple of lines and I have no idea what the proper syntax would be (and the freepascal wiki, has very little information on the assembler directives themselves).

I will of course be grateful to anybody helping me solve this problem and send a very nice 'thank you' email :-)

Wkr,

The function you want is InterlockedCompareExchange(), which is defined in the system unit: http://www.freepascal.org/docs-html/rtl/system/interlockedcompareexchange.html

It does what cmpxchg does, and moreover is cross-platform.

Jonas

Cool !!! Thanks a lot for the info. This is exactly what I was looking for !