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

Subject: Re: [Boost-users] [boost] Boost.Fiber mini-review September 4-13
From: Hartmut Kaiser (hartmut.kaiser_at_[hidden])
Date: 2015-09-05 14:31:09

>>> it seams to me that it makes not sense that boost.fiber tries to re-
>>> implement HPX's strategy.
>>> if a user requires migration of fibers he can use HPX, if the user has to
>>> use TLS in its code (fiber-fn) and
>>> wants an std::thread-like API (== this_fiber::yield(), mutex,
>>> condition_variable ...) he can choose
>>> boost.fiber.

>From this perspective there wouldn't be a need for Boost.Fiber in the first place as all of this (yield, mutex, condvar, etc.) is implemented in HPX already.

>>> at the moment I don't see a possibility to eliminate the TLS-requirement
>>> for fiber_manager

Too bad, I was hoping we could reuse it in HPX :/

>> Yes, we have a slightly different approach. All HPX Fibers are called from
>> within a scheduling loop. A yield is therefor just a context switch back
>> to the scheduling loop, no lookup required.
> 
> so HPX's scheudling loop runs in the main-context (e.g. main() or thread-
> fn) - in contrast boost.fiber handles the main-fiber (main() or thread-fn)
> as a fiber too.
> e.g. the main-fiber can be suspended, stored, resumed int the same way as
> ordinary fibers (ordinary fibers == nedd to allocate fiber-stack, created
> via fiber ctor).
> thus the difference between main-fiber and ordinary fibers (created via
> fiber ctor) is that the main-fiber has already a stack (provided and
> assigned by the os) assigned

HPX has no 'main' context. It requires for the user to supply a special hpx_main() function which is used as the application's main() and which is already a fiber.

// This is executed as the first fiber 
int hpx_main(int argc, char* argv)
{
    // ...your app goes here...

    // signal end of execution to the runtime
    return hpx::finalize();
}

int main(int argc, char* argv)
{
    // start runtime and wait for it to finish
    return hpx::init(argc, argv);
}

HTH
Regards Hartmut
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