From: Vladimir Davydov <vdavydov.dev@gmail.com>
To: Serge Petrenko <sergepetrenko@tarantool.org>
Cc: tarantool-patches@freelists.org
Subject: Re: [PATCH v3] Fix fiber_join() hang in case fiber_cancel() was called
Date: Wed, 6 Feb 2019 17:09:33 +0300 [thread overview]
Message-ID: <20190206140933.ses3gvmayt3u3d4c@esperanza> (raw)
In-Reply-To: <20190206125630.58091-1-sergepetrenko@tarantool.org>
On Wed, Feb 06, 2019 at 03:56:30PM +0300, Serge Petrenko wrote:
> In case a fiber joining another fiber gets cancelled, it stays suspended
> forever and never finishes joining. This happens because fiber_cancel()
> wakes the fiber and removes it from all execution queues.
> Fix this by adding the fiber back to the wakeup queue of the joined
> fiber after each yield.
>
> Closes #3948
> ---
> https://github.com/tarantool/tarantool/issues/3948
> https://github.com/tarantool/tarantool/tree/sp/gh-3948-fiber-cancel-during-join
>
> Changes in v3:
> - rewrote the test with fiber channel
> to remove scheduler dependency.
> - went back to ignoring cancellation
> till join is complete.
>
> Changes in v2:
> - rewrote the test completely.
> - instead of continuing to join if the fiber
> is cancelled make the fiber to be joined
> non-joinable and exit. This solution was
> discussed verbally.
> - revert comment changes for fiber_yield().
> It really isn't a cancellation point.
>
> src/fiber.c | 12 ++++++++++--
> test/app/fiber.result | 43 +++++++++++++++++++++++++++++++++++++++++
> test/app/fiber.test.lua | 21 ++++++++++++++++++++
> 3 files changed, 74 insertions(+), 2 deletions(-)
>
> diff --git a/src/fiber.c b/src/fiber.c
> index 6f3d0ab78..70e992f13 100644
> --- a/src/fiber.c
> +++ b/src/fiber.c
> @@ -392,9 +392,17 @@ fiber_join(struct fiber *fiber)
> assert(fiber->flags & FIBER_IS_JOINABLE);
>
> if (! fiber_is_dead(fiber)) {
> - rlist_add_tail_entry(&fiber->wake, fiber(), state);
> -
> do {
> + /*
> + * In case fiber is cancelled during yield
> + * it will be remoed from wake queue by a
> + * wakeup following the cancel, so we have
> + * to put it back in.
> + * Having multiple queue entries for the
> + * same fiber doesn't hurt, since wakeup
> + * is executed only once per fiber.
> + */
> + rlist_add_tail_entry(&fiber->wake, fiber(), state);
I removed the second paragraph of the comment, because it's confusing,
and pushed the patch to 2.1 and 1.10.
prev parent reply other threads:[~2019-02-06 14:09 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-02-06 12:56 Serge Petrenko
2019-02-06 14:09 ` Vladimir Davydov [this message]
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