Re: [boost] boost lockfree queue.hpp - alternate implementation w/o compare_exchange

Subject: Re: [boost] boost lockfree queue.hpp - alternate implementation w/o compare_exchange
From: boost_at_[hidden]
Date: 2015-10-23 14:27:58

On 2015-10-22 02:57, Giovanni Piero Deretta wrote:
> On 22 Oct 2015 3:26 a.m., <boost_at_[hidden]> wrote:
>>> 
> 
>> 
>> The yield can be removed without any ill effect except in cases of
> over-subscription.  Without the yield performance is *very* poor 
> because
> the thread is forced to wait for other threads that aren't even running
> (lines 355 & 378)...  Basically the yield is only a work-around for
> something that is undesirable anyway (over-subsciption), but it limits 
> the
> 'damage' in those scenarios.
> 
> It seems to me then it is not really lock free then, right?

That is an interesting viewpoint, and in the perspective of over 
subscription I suppose you have a point in a certain sense.  All writers 
allowed to enter push or readers allowed to enter pop can do all their 
work in parallel except to increase the trailing edge (write/read 
position essentially).  Each writer (and symmetrically reader)has to 
wait for the writer before it before increasing the queue size (and 
allowing a reader).