Wouldn't a simple

return execution::async_execute(policy.executor(),  
    &sort_thread<ExPolicy, RandomIt, Compare>,  
    std::ref(policy), first, last, comp);

do the trick here?

@hkaiser You're right. That code was derived from just moving return result; into inside of try block. I'll fix that like you said.

Hmmm, do we really have to use nested try/catch blocks here? handle_local_exceptions only rethrows the current exception as an exception list. Couldn't we directly call make_exceptional_future with a exception list constructed from the current exception?

@hkaiser handle_local_exceptions() handles an exception differently when std::current_exception() means std::bad_alloc. In that case, handle_local_exceptions() just rethrows std::bad_alloc without wrapping into exception_list.
We need to handle the exception differently according to what is the exception which we handles. And for that, I used handle_local_exception().
And nested catch (Line216-219) is needed for wrapping an exception which is threw properly from handle_local_exception().

@taeguk yes, I understand. Still, there might be a better way.

@hkaiser Aha, okay i got it.
https://github.com/taeguk/hpx/blob/9d72e4de54495987597bc2e6bbe609bc8125a01c/hpx/parallel/algorithms/sort.hpp#L249-L260
If we move that exception handling from Line208 to above lines, we can avoid nested try/catch blocks with just calling detail::handle_exception().

For example, https://github.com/taeguk/hpx/blob/9d72e4de54495987597bc2e6bbe609bc8125a01c/hpx/parallel/algorithms/partition.hpp#L963-L975

Hmm, this looks really strange (it probably was strange all along). I'm sure this can be done with one level of try/catch blocks.

@hkaiser Yes, we can do that with only one level of try/catch blocks.