About lockfree_mpmc ...

About lockfree_mpmc ...

Hello all,

I think i have discovered a problem with lockfree_mpmc:

You will find the source code of lockfree_mpmc at:

http://pages.videotron.com/aminer/

So please follow with me:

If you take a look at the lockfree_mpmc , here is the source code
of the push() method:

---

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;

newTemp:=LockedIncLong(temp);

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

repeat

if CAS(tail,lasttail,newtemp)
then
begin
exit;

end;
sleep(0);
until false;

end;

---

As you know in the x86 architectureLoads may be reordered with older
stores
to different locations.

So in line[2] there is a load of tail and lasttail to the registers of the
processor
before calling setobject()and just before on line [1] there is a store
tolasttail.

So as you have noticed the processor can then reorder the loads on line [2]
with the older
store on line[1] and this will cause a problem, so i thinki have to
insert a load between
line [1] and line [2].

What do you think ?

Sincerely,
Amine Moulay Ramdane.

3 posts / 0 new
Last post
For more complete information about compiler optimizations, see our Optimization Notice.

I wrote:
> So as you have noticed the processor can then reorder the loads on
line [2]
> with the older
> store on line [1] and this will cause a
problem, so i think i have to insert
> a load between
> line [1]
and line [2].

Even if i insert a load beween line [1] and [2] this will not work ,
i have to insert an mfence between line [1] and [2].

What do you think ?

Sincerely,
Amine Moulay Ramdane.

Hello,

I have inserted an mfence between line [1] and [2] in lockfree_mpmc andi
have
updated all my programs that uses lockfree_mpmc,and you can download all

the source codes of my programs from:

http://pages.videotron.com/aminer/

Sincerely,
Amine Moulay Ramdane.

Leave a Comment

Please sign in to add a comment. Not a member? Join today