From: Greg Colvin (gcolvin_at_[hidden])
Date: 2000-08-31 23:20:05
From: Valentin Bonnard <Bonnard.V_at_[hidden]>
> On Thu, Aug 31, 2000 at 12:30:22PM -0400, David Abrahams wrote:
> >
> > From: "William Kempf" <sirwillard_at_[hidden]>
> > > > The following Win32 functions don't work right on Win95:
> > > >
> > > > InterlockedCompareExchange
> > > > InterlockedCompareExchangePointer
> > > > InterlockedExchangeAdd
> > >
> > > But they do on Win98. Tricky issue here. I included the
> > > compare_exchange() only to bring up debate about its usefulness.
> > > I've never found a need for them, but didn't want to eliminate them
> > > just because I've never needed them, nor because Win95 didn't support
> > > them. Obviously they can be added to Win95 in the form of some
> > > assembler instructions.
> >
> > Just an additional data point: if I remember correctly, the Motorola 680x0,
> > where x > 2, includes atomic instructions for linking list elements in/out
> > of singly- and doubly-linked lists! These are called something like
> > "Atomic-compare-and-exchange" IIRC.
>
> Insert in singly linked list:
>
> inserted->next = pos->next;
> pos->next = inserted;
>
> This can't be done atomically, even which get_and_set (but each assignment
> can be done atomically)
>
>
> Remove from singly linked list:
>
> // at this point removed_prev.next == removed
> removed_prev->next = removed->next;
>
> MOVE (next,removed), (next,removed_prev)
>
> (Atomic on every 68k)
>
>
> Remove from doubly linked list:
>
> removed->prev->next = removed->next;
> removed->next->prev = removed->prev;
>
> IMO this can't be done atomically (but each assignment can be done
> atomically).
I looked in my 68020 manual and couldn't figure out how to
do it either, but there maybe a trick I don't know.
Here is how I once did it for a singly-linked list with
compare/exhange for an x86 memory manager:
static inline MemCell* PopFreeCell(MemCell** ppFree)
{
// while free list available spin until free cell is obtained
_asm {
mov edi, ppFree
mov eax, [edi]
spin:
test eax, eax
jz done
mov esi, [eax]
lock cmpxchg [edi], esi
jnz spin
done:
}
}
static inline void PushFreeCell(MemCell** ppFree,void* p)
{
// spin until cell put at head of free list
_asm {
mov edi, ppFree
mov eax, [edi]
mov esi, p
spin:
mov [esi], eax
lock cmpxchg [edi], esi
jnz spin
}
}
The VAX has some instructions for the purpose as well.