ichthyo/LUMIERA.clone
1
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Library: extract hook argument adaption

Browse source 
extract into helper function to improve legibility.

This code is rather tricky since on invocation the hook is only provided
but not invoked. Rather, to adapt the argument types, it is wrapped
into a λ for adaptation, which then must be again bound *by value*
into yet another λ, since the Launch configuration builder is comprised
of a chain of captured functors, to be invoked later from the body of the
thread-wrapper object; this indirect procedure is necessary to ensure
all members are initialised *before* the new thread starts
This commit is contained in:
Fischlurch 2023-10-10 20:07:35 +02:00
parent 8b3f9e17cd
commit fad02bd00e
1 changed files with 36 additions and 21 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

57
src/lib/thread.hpp
View file

@ -495,36 +495,51 @@ namespace lib {
}
private:
/**
* Helper to adapt a user provided hook to be usable as lifecycle hook.
* @tparam HOOK type of the user provided λ or functor
* @tparam FUN type of the function maintained in #PolicyLifecycleHook
* @note the user provided functor can take any type as argument, which
* is reachable by static cast from the thread-wrapper. Especially
* this allows both for low-level and userclass-internal hooks.
*/
template<typename HOOK, class FUN>
auto
adaptedHook (FUN Policy::*, HOOK&& hook)
{
static_assert(1 == _Fun<FUN>::ARITY);
static_assert(1 >= _Fun<HOOK>::ARITY);
// argument type expected by the hooks down in the policy class
using Arg = typename _Fun<FUN>::Args::List::Head;
// distinguish if user provided functor takes zero or one argument
if constexpr (0 == _Fun<HOOK>::ARITY)
return [hook = forward<HOOK>(hook)](Arg){ hook(); };
else
{ // instance type expected by the user-provided hook
using Target = typename _Fun<HOOK>::Args::List::Head;
return [hook = forward<HOOK>(hook)]
(Arg& threadWrapper)
{ // build a two-step cast path from the low-level wrapper to user type
ThreadLifecycle& base = static_cast<ThreadLifecycle&> (threadWrapper);
Target& target = static_cast<Target&> (base);
hook (target);
};
}
}
/** add a config layer to store a user-provided functor into the polic baseclass(es) */
template<typename HOOK, class FUN>
Launch&&
addHook (FUN Policy::*storedHook, HOOK&& hook)
{
static_assert(1 == _Fun<FUN>::ARITY);
static_assert(1 >= _Fun<HOOK>::ARITY);
using Arg = typename _Fun<FUN>::Args::List::Head;
FUN adapted;
if constexpr (0 == _Fun<HOOK>::ARITY)
{
adapted = [hook = forward<HOOK>(hook)](Arg){ hook(); };
}
else
{
using Target = typename _Fun<HOOK>::Args::List::Head;
adapted = [hook = forward<HOOK>(hook)]
(Arg& threadWrapper)
{
ThreadLifecycle& base = static_cast<ThreadLifecycle&> (threadWrapper);
Target& target = static_cast<Target&> (base);
hook (target);
};
}
return addLayer ([storedHook, hook = move(adapted)]
return addLayer ([storedHook, hook = adaptedHook (storedHook, forward<HOOK> (hook))]
(ThreadLifecycle& wrapper)
{
wrapper.*storedHook = move(hook);
wrapper.*storedHook = move (hook);
});
}
/** generic helper to add another »onion layer« to this config builder */
Launch&&
addLayer (Act action)
{