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

Subject: Re: [Boost-users] [boost] Boost.Fiber mini-review September 4-13
From: Oliver Kowalke (oliver.kowalke_at_[hidden])
Date: 2015-09-05 16:29:34

2015-09-05 22:04 GMT+02:00 Hartmut Kaiser <hartmut.kaiser_at_[hidden]>:

> >> a) is safe as all threads sharing the same scheduler store the same
> >> reference (fibers can be moved only inside that scheduler)
> >> b) is safe as the runtime sets the reference to the fiber it is about to
> >> run in TLS and resets it right after the fiber returned.
> >
> > but I was asking for the code snipped which accesses TLS variable - if
> all
> > threads share the same scheduler why has it to be stored in TLS?
> > a slight modification of my example above - replace
> > retrn_ptr_of_scheduler_thread_lcoal_var() by return_ptr_to_active_fiber()
> > I assume that as you mentioned in b) that the active fiber is stored in
> > TLS - the exmaple code prints out the address of the current active fiber
> > how does the code look like after compiler optimization?
>
> I don't know. We have never ran into any problems related to this.
>

hmm, that's strange because I got those problems as I implemented support
for migrating fibers.

after optimization the code form the example looks like this:

void bar( Fiber * f) {
   printf("%p\n", f);;
   suspend_and_migrate();
}

void foo() {
    Fiber * f = return_ptr_to_active_fiber();
    while( true) {
        bar( f);
    }
}

the code is translated back from assembler (g++ -S -std=c++11 -O1
test_tls.cpp)