[fpc-pascal] getting started with threads

[Helmut Hartl]

-----Original message-----
From: Dariusz Mazur <darekm at emadar.com>
Sent: Fri 18-09-2009 16:24
To: FPC-Pascal users discussions <fpc-pascal at lists.freepascal.org>; 
Subject: Re: [fpc-pascal] getting started with threads

> David Emerson pisze:
> > I am getting started with threads (linux/cthreads) and I'm very happy so 
> > far, but unsure of the best way to tackle my situation.
> >
> > I have a program that needs to perform about 10,000 independent tasks, 
> > which usually involve waiting for I/O; thus it makes sense to use 
> > several threads so that some waiting can be done in parallel. I thought 
> > I'd try it with 10 threads.
> You need FIFO queue for multiple consumer. Each task can be assigned to 
> them.
> You can use ordinal tThreadList but it rather slow.
> 
> I use own lockfree FIFO http://www.emadar.com/fpc/lockfree.htm to 
> distribute task between threads
> its much faster and well scaling on multicore.


I had (only) a quick look at your implementation but i have the
bad feeling that it suffers from the ABA problem. Normally it has a 
low probability to occur but nevertheless extremely hard to find errors 
occur occasionally.
The problem is avoided by using a 64 Bit CAS with a tagged pointer.
I have such a implementation under BSD Licence which i can donate for
review and public use. But it only works for 32 Bit x86 archs by now,
as i am not sure if there is a consistent support of a 128 Bit CAS on 
all x86 chips. (my last knowledge was that not all xeon/pentium steppings support it)

Have a look at (as example): http://www.cs.rochester.edu/~scott/papers/1996_PODC_queues.pdf

Lot's of interesting publications in the field can be found at the ACM (http://www.acm.org/),
but you need to be member to have access to the digital library.

helmut