[fpc-pascal] getting started with threads

Dariusz Mazur darekm at emadar.com
Sat Sep 19 10:16:24 CEST 2009

Helmut Hartl pisze:
> -----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.
Its save about ABA problem, only it atomic operation are true atomic. I 
try to test both: theoretical and in real. But if You know sequence, 
that things may go wrong, pleas tell it.
> 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)
64bit CAS is absent on many platforms, and is slower
but I'd like too see Your implementation
> 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.
thx for links


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