About lockfree_mpmc ...

About lockfree_mpmc ...

Hello,

I think i have forgot something with lockfree_mpmc...

Please follow with me...

The Intel x86 memory model, detailed in Intel 64 Architecture Memory Ordering White Paper
and the AMD spec, AMD64 Architecture Programmers Manual, list a lot of memory ordering
guarantees, among them:

Loads are not reordered with other loads.
Stores are not reordered with other stores.
Stores are not reordered with older loads.
In a multiprocessor system, memory ordering obeys causality (memory ordering respects transitive visibility).
In a multiprocessor system, stores to the same location have a total order.
In a multiprocessor system, locked instructions have a total order.
Loads and stores are not reordered with locked instructions.

But since on x86 Loads may be reordered with older stores to different locations

So please take a look at the following lockfree_mpmc code:

---

function TLockfree_MPMC.push(tm : tNodeQueue):boolean;
var lasttail,newtemp:long;
i,j:integer;
begin

if getlength >= fsize
then
begin
result:=false;
exit;
end;
result:=true;

[1]newTemp:=LockedIncLong(temp);

[2] lastTail:=newTemp-1;
setObject(lastTail,tm);

[3]

repeat

[4] if CAS(tail,lasttail,newtemp)
then
begin
exit;
end;
sleep(0);
until false;

end;
---

So the the loads of lasttail and newtemp in [4] line can be reordered
with older stores of lastail and newtemp in [1] [2], so in this case must
i insert an mfence in line [3] to respect the logic of the program?...

Thank you,
Amine Moulay Ramdane.

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Hello again,

Sorry, as you have noticied there is loads on
setObject(lastTail,tm)between line [2] and line [4].

And loads are not reordered with older loads on x86

So i think there is no problemwith lockfree_mpmc.

Thank you.
Amine Moulay Ramdne

Hello again,

Sorry, as you have noticied there is loads on
setObject(lastTail,tm) between line [2] and line [4].

And loads are not reordered with older loads on x86

So i think there is no problem with lockfree_mpmc.

Thank you.
Amine Moulay Ramdne

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