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Beginner
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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:
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.
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2 Replies
Highlighted
Beginner
7 Views


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.
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Highlighted
Beginner
7 Views


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:
Sincerely,
Amine Moulay Ramdane.
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