13:25 <sestro[m]> Hi, is there an easy way to create a "task-local" variable in HPX? I'm looking for the equivalent to `thread_local` but for HPX tasks. The use case is to have a variable shared between all iterations in a `hpx::for_loop` performed by the same task. Or would I manually create the chunks over the loop index and add the variable at this level?

13:27 <hkaiser> sestro[m]: there is get/set_thread_data that allows to attach a size_t to a hpx thread

13:27 <hkaiser> but this is very low level

13:28 <hkaiser> sestro[m]: do you need a variable for some collective operation?

13:29 <sestro[m]> hkaiser: I need a sort of a lookup cache, but only for the scope of each individual task, so not shared between tasks.

13:30 <hkaiser> would creating the cache on the stack of that task work? or do you need to access it after the task ended as well?

13:31 <sestro[m]> No, that should work.

13:31 <hkaiser> might be the easiest solution...

13:31 <sestro[m]> true, thanks!

13:47 <ms[m]> gnikunj: just in case, kokkos meeting started now

15:21 <sestro[m]> hkaiser: sry, had to run before. regarding the stack allocation: unless I'm missing something here (which most likely is the case) allocating the cache on the stack within the functor passed to `hpx::for_loop` would mean the object is created for each single iteration. this is what I'm trying to avoid.

15:24 <sestro[m]> but I did find https://github.com/STEllAR-GROUP/hpx/blob/master/examples/quickstart/safe_object.cpp

15:26 <sestro[m]> is there a guarantee that a HPX task, once scheduled for execution, cannot jump between OS threads?

15:31 <hkaiser> sestro[m]: you said you needed it for every 'thread'

15:31 <hkaiser> so you need it for every 'chunk'?

15:31 <hkaiser> why not use thread_locals, then?

15:32 <hkaiser> and yes, safe_object is doing just that

15:33 <sestro[m]> hkaiser: at least for every chunk, sorry for not being clear before. but for every thread also works.

15:34 <sestro[m]> I incorrectly assumed thread_local wouldn't work as I wasn't aware of the fact that tasks cannot jump between OS threads

15:35 <hkaiser> tasks may jump between kernel-threads

15:35 <hkaiser> but if it's caching you're intersted in this shouldn't be a problem

15:36 <sestro[m]> but the cached entries may be task-specific

15:36 <hkaiser> hmmm

15:36 <sestro[m]> so I'd like to avoid switching between different caches

15:37 <hkaiser> sestro[m]: there is this: https://github.com/STEllAR-GROUP/hpx/blob/master/examples/quickstart/executor_with_thread_hooks.cpp

15:38 <hkaiser> that allows to do things specificly to the chunks

15:39 <sestro[m]> ah, okay. will have a look at that, thanks