Subject: Re: [boost] [Fibers] Performance
From: Nat Goodspeed (nat_at_[hidden])
Date: 2014-01-16 08:27:42
On Thu, Jan 16, 2014 at 7:51 AM, Giovanni Piero Deretta
<gpderetta_at_[hidden]> wrote:
> I think that Harmut point is that you can very well use threads for the
> same thing. ...
> The point of using fibers (i.e. M:N threading) is almost purely
> performance.
Again, for a large class of use cases, fibers and threads are not the same.
Writing thread-safe code remains something of an art, a specialty
within the already-rarefied realm of good C++ coding. With care, code
review and testing, it is of course possible to produce good
thread-safe code when you are writing it from scratch.
But retrofitting existing single-threaded code to be thread-safe can
be extremely costly. At this moment in history, we have a very large
volume of existing code whose developers (perhaps unconsciously)
relied on having exclusive access to certain in-process resources.
Some of us do not have the option to discard it and rewrite from
scratch.
Yes, this is a subset of the possible use cases of the Fiber library.
It is an important subset because threads provide no equivalent.
Yes, I also want a Boost library that will concurrently process very
large numbers of tasks, with each of a number of threads running very
many fibers. I think the Fiber library gives us a foundation on which
to build that support. But even with its present feature set, with
Oliver responding to the community, it has great value. I feel
frustrated when people dismiss the very real benefit of cooperative
context switching as irrelevant to them.