From: Vladislav Shpilevoy via Tarantool-patches <tarantool-patches@dev.tarantool.org>
To: Cyrill Gorcunov <gorcunov@gmail.com>,
tml <tarantool-patches@dev.tarantool.org>
Subject: Re: [Tarantool-patches] [PATCH v2 2/2] fiber: fiber_join -- don't crash on misuse
Date: Wed, 28 Apr 2021 23:16:20 +0200 [thread overview]
Message-ID: <c5006b29-8211-262c-bf15-4a711c2c2ada@tarantool.org> (raw)
In-Reply-To: <20210428102251.552976-3-gorcunov@gmail.com>
> diff --git a/src/lua/fiber.c b/src/lua/fiber.c
> index 02ec3d158..0c8238cab 100644
> --- a/src/lua/fiber.c
> +++ b/src/lua/fiber.c
> @@ -791,9 +793,11 @@ lbox_fiber_join(struct lua_State *L)
> int num_ret = 0;
> int coro_ref = 0;
>
> - if (!(fiber->flags & FIBER_IS_JOINABLE))
> - luaL_error(L, "the fiber is not joinable");
> - fiber_join(fiber);
> + if (fiber_join(fiber) != 0) {
> + e = diag_last_error(&fiber()->diag);
> + if (e->type == &type_IllegalParams)
> + luaL_error(L, e->errmsg);
After looking at this hunk I realized that it might be wrong to
allow to call join on a non-joinable fiber. Firstly, you have no
way to check why did join return -1: because it wasn't joinable
or because this is what the fiber's function has returned. It is
simply impossible in the public API (module.h).
Secondly, fiber_join() is documented to always return the
fiber's function result. I see it in module.h and on the site.
Here the behaviour has kind of changed - it might return something
even if the fiber didn't really end. This is especially bad if the
fiber was using some resources which are freed right after the join.
And doubly-bad if the user's function never fails, so fiber_join()
result wasn't even checked in his code.
Thirdly, this leads to inconsistent behaviour. In this example
fiber.join does not raise an error - it returns false + error:
fiber = require('fiber')
do
f = fiber.new(function() box.error('other error') end)
f:set_joinable(true)
end
tarantool> f:join()
---
- false
- '[string "do..."]:2: box.error(): bad arguments'
...
But when I change the error type, it raises the error:
fiber = require('fiber')
do
f = fiber.new(function() box.lib.load() end)
f:set_joinable(true)
end
tarantool> f:join()
---
- error: Expects box.lib.load('name') but no name passed
...
It didn't happen before your patch. The same problem exists for
fiber_join_timeout(), but at least it is documented to be able to
return before the fiber has joined.
With that said, I think we must call panic() on an attempt to join
a non-joinable fiber.
For easier usage we might need to introduce fiber_join_ex(), which
wouldn't mix its own fail and the fiber's function fail. But maybe
not now since nobody really asked for that.
next prev parent reply other threads:[~2021-04-28 21:16 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-28 10:22 [Tarantool-patches] [PATCH v2 0/2] fiber: prevent fiber_join from misuse Cyrill Gorcunov via Tarantool-patches
2021-04-28 10:22 ` [Tarantool-patches] [PATCH v2 1/2] fiber: fiber_join -- drop redundat variable Cyrill Gorcunov via Tarantool-patches
2021-04-28 15:13 ` Serge Petrenko via Tarantool-patches
2021-04-28 10:22 ` [Tarantool-patches] [PATCH v2 2/2] fiber: fiber_join -- don't crash on misuse Cyrill Gorcunov via Tarantool-patches
2021-04-28 15:13 ` Serge Petrenko via Tarantool-patches
2021-04-28 15:21 ` Cyrill Gorcunov via Tarantool-patches
2021-04-28 15:34 ` Serge Petrenko via Tarantool-patches
2021-04-28 21:16 ` Vladislav Shpilevoy via Tarantool-patches [this message]
2021-04-28 22:12 ` Cyrill Gorcunov via Tarantool-patches
2021-04-29 11:10 ` [Tarantool-patches] [PATCH v3 " Cyrill Gorcunov via Tarantool-patches
2021-04-29 19:37 ` Vladislav Shpilevoy via Tarantool-patches
2021-04-29 20:39 ` Cyrill Gorcunov via Tarantool-patches
2021-04-29 21:10 ` Vladislav Shpilevoy via Tarantool-patches
2021-04-30 8:13 ` [Tarantool-patches] [PATCH v2 0/2] fiber: prevent fiber_join from misuse Kirill Yukhin via Tarantool-patches
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