Re: [boost] Boost.Fiber mini-review September 4-13

Subject: Re: [boost] Boost.Fiber mini-review September 4-13
From: Thomas Heller (thom.heller_at_[hidden])
Date: 2015-09-04 17:32:47

On 09/04/2015 10:52 PM, Nat Goodspeed wrote:
> On Fri, Sep 4, 2015 at 4:33 PM, Thomas Heller <thom.heller_at_[hidden]> wrote:
>
>> On 09/04/2015 10:03 PM, Oliver Kowalke wrote:
>
>>> it is safe to call boost::this_fiber::yield() from main(), e.g. each
>>> thread has a main-context/main-fiber
>
>> Ok makes sense. So on a non-fiber context this is essentially a noop? Might
>> be a good idea to add this to the documentation.
>
> If I may attempt to clarify your feedback:
>
> I think you're suggesting that the documentation doesn't yet make
> clear that this_fiber operations, such as yield(), are valid from
> main() and from each new thread function, as well as from
> explicitly-launched fibers. Good point.
>
> I'm not sure I understand what you mean by a non-fiber context. In
> effect, main() is running on the default fiber for the application's
> main thread. Similarly, at entry to a thread function, code is running
> on the default fiber for that thread. If you call this_fiber::yield()
> without yet having launched any other fibers, it's effectively a
> no-op: control detours through the fiber manager and the scheduler,
> which concludes that there's only one ready fiber, so the yield() call
> returns at once. But such a call is indeed meaningful once you launch
> other fibers.

Ahh, that makes sense and is a nice behavior. I wasn't aware of that.
What I meant with "fiber execution context" is indeed something that is 
implemented in boost::fiber::fiber_manager::active_fiber_. However, my 
assumption was that this tss variable is only valid in task created with 
boost.fiber (That's what I'm used to). I think at one place or another.

>
> If the documentation were to clarify that yield (et al.) are valid
> from main() (et al.), would that address your concern, or would you
> also want to see something like the more verbose paragraph above?

I think the reference documentation would be fine with just a small 
sentence from where they are valid from. That verbose paragraph is 
probably useful in some form of exmaple/tutorial. This information is 
extremely valuable if you want to await busy-wait loops, for example to 
implement some exponantial backof scheme as the one necessary in the 
non-allocating futures.

>
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