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.
