Martin Friebe pisze:
You will need to test it, but the following may also work
procedure tFlQueue.push(const tm : tNodeQueue);
var
newTemp,
lastTail,
newTail : integer;
begin
newTemp := temp;
while newTemp >= fsize begin
// if it is true, every thread is going to attempt to fix it,
before doing the increment.
// this means no thread will increase the value
// => one thread will to succeed (since the only reason "temp NE
newTemp" is that temp has been decreased)
// newTemp is bigger than fsize, so the result can not become
negative.
interlockedCompareExchange(pointer(temp),pointer(newTemp-fsize),pointer(newTemp));
newTemp := temp;
end;
newTemp:=interlockedIncrement(temp) mod fsize; // make sure we are
always in range
lastTail:=newTemp-1;
if lastTail < 0 then lastTail := fsize -1;
setObject(lastTail,tm); // you can remove the "mod" in setobject
repeat
pointer(newTail):=interlockedCompareExchange(pointer(tail),pointer(newTemp),pointer(lastTail));
until (newTail=lastTail);
end;
It seems ok, but then we have 2 IF more.
And the same should repeat with pop
The "repeat" at the end does still work. In order to set "tail" to "0"
(newTemp=0) => "tail" must first get "9" (as lastTail will be 9).
Only flaw is, if fsize is close enough to the upper data tpye
boundary, and enough threads do InterLockedInvrement, (after all
having simultaneously passed the repeat at the start), then you can
still run over the boundary.
However this can only happen if you have more threads, than
(upperBoundary - fsize).
So you can specify, that it is save up to this amount of parallel threads
Because we cant change size of queue in run, we have to make it so big
that always will be enough.
For me it should be ten time bigger, than observe maximum (1000 its only
4 kB of ram).
IMHO the unit should have a warning (in the comments) that there it is
the users responsibility *not* to store more elements than fsize.
There is no check, and you will loose data, if you try to do so.
Ok, Ive write warning in source
And i've upload new version of program.
Darek
_______________________________________________
fpc-devel maillist - fpc-devel@lists.freepascal.org
http://lists.freepascal.org/mailman/listinfo/fpc-devel
