# How to interrupt tasks of DomainsLib? **URL:** \ **Category:** Learning\ **Tags:** domainslib, parallel-programming\ **Created:** [November 13, 2024, 1:11pm UTC](https://discuss.ocaml.org/t/how-to-interrupt-tasks-of-domainslib/15603 "2024-11-13T13:11:37Z")\ **Posts on this page:** 2\ **Page:** 1
**Author:** ![Kakadu](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/kakadu/32/1204_2.png) [@Kakadu](https://discuss.ocaml.org/u/Kakadu)\ **Post date:** [November 13, 2024, 1:11pm UTC](https://discuss.ocaml.org/t/how-to-interrupt-tasks-of-domainslib/15603/1 "2024-11-13T13:11:37Z")
We have issues with interruption of our parallel program in OCaml 5.2 (+flambda). Our programs runs many tasks via `Domainslib.Task.parallel_for` and we want to interrupt and print currently found data via Ctrl-C. I can’t find any suitable API for interruption in Domainslib, so I added old school `Sys.(set_signal sigint) (Signal_handle (fun _ -> ....))`. In the handler we don’t do anything about Domainslib, we handle already produced data by OCaml code and some Z3 calls. Sometimes it interrupts OK, but sometimes doesn’t: - Sometimes a process hangs and don’t print stuff should be printed in handler. We tried to attach via GDB, a backtrace is in the end of the post. - Sometimes we get crashes like `IOT instruction (core dumped) ` - Sometimes libc crashes with `double free or corruption (!prev)` - Sometimes `malloc(): unaligned tcache chunk detected` We tried to change signal fro SIGINT to SIGUSR1 and it looks like the latter works (i.e. we didn’t observe any crashes). Questions: 1. How to properly interrupt tasks of `Domainslib`? 2. Are we allowed to make external C calls in a signal handler? 3. Any idea why SIGUSR1 may work better? > **GDB backtrace** > > ```auto > #0 0x0000597213f035ef in frame_return_to_C (d=) at runtime/caml/frame_descriptors.h:80 > #1 scan_stack_frames (fflags=(unknown: 0x90d42c00), gc_regs=, stack=0x597217064960, fdata=, > f=) at runtime/fiber.c:255 > #2 caml_scan_stack (f=f@entry=0x597213f13980 , fflags=fflags@entry=(unknown: 0x90d42c00), > fdata=fdata@entry=0x7ffe0ada17d0, stack=0x597217064960, stack@entry=0x597214d6bb40, gc_regs=0x597214d86980, > gc_regs@entry=0x74682da68010) at runtime/fiber.c:285 > #3 0x0000597213f16e25 in caml_do_local_roots (f=f@entry=0x597213f13980 , fflags=(unknown: 0x90d42c00), > fflags@entry=SCANNING_ONLY_YOUNG_VALUES, fdata=fdata@entry=0x7ffe0ada17d0, local_roots=, > current_stack=0x597214d6bb40, v_gc_regs=0x74682da68010) at runtime/roots.c:69 > #4 0x0000597213f1451c in caml_empty_minor_heap_promote (domain=domain@entry=0x597214d6bb60, > participating_count=participating_count@entry=5, participating=participating@entry=0x59721426b4e0 ) > at runtime/minor_gc.c:609 > #5 0x0000597213f14876 in caml_stw_empty_minor_heap_no_major_slice (domain=0x597214d6bb60, participating_count=5, > participating=0x59721426b4e0 , unused=) at runtime/minor_gc.c:746 > #6 0x0000597213eff580 in stw_handler (domain=0x597214d6bb60) at runtime/domain.c:1385 > #7 handle_incoming (s=) at runtime/domain.c:340 > #8 0x0000597213effdc0 in caml_handle_incoming_interrupts () at runtime/domain.c:353 > #9 caml_handle_gc_interrupt () at runtime/domain.c:1774 > #10 0x0000597213f1a58b in caml_do_pending_actions_exn () at runtime/signals.c:341 > #11 caml_process_pending_actions_with_root_exn (root=, root@entry=1) at runtime/signals.c:386 > #12 0x0000597213f1a632 in caml_process_pending_actions_with_root (root=1) at runtime/signals.c:395 > #13 caml_process_pending_actions () at runtime/signals.c:406 > #14 > #15 0x0000597213e2d6e5 in camlStdlib__Set.mem_530 () at set.ml:251 > > ``` ---
**Author:** ![dinosaure](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.ocaml.org/dinosaure/32/16_2.png) [@dinosaure](https://discuss.ocaml.org/u/dinosaure)\ **Post date:** [November 13, 2024, 2:02pm UTC](https://discuss.ocaml.org/t/how-to-interrupt-tasks-of-domainslib/15603/2 "2024-11-13T14:02:45Z")
> [@Kakadu](#): > > Our programs runs many tasks via `Domainslib.Task.parallel_for` and we want to interrupt and print currently found data via Ctrl-C. I could advise you to use [Miou](https://github.com/robur-coop/miou), which allows you to use a pool of domains and run tasks in parallel with [Miou.parallel](https://ocaml.org/p/miou/latest/doc/Miou/index.html#val-parallel). Miou also implements task cancellation, so using [Miou.call](https://ocaml.org/p/miou/latest/doc/Miou/index.html#val-call) / [Miou.cancel](https://ocaml.org/p/miou/latest/doc/Miou/index.html#cancellation.) should satisfy you. It is also possible, as explained [in this short tutorial](https://robur-coop.github.io/miou/conditions_and_mutexes.html#conditions), to manage signals such as Ctrl-C.