Re: [Tarantool-patches] [PATCH v2] core: handle fiber cancellation for fiber.cond

["Alexander V. Tikhonov" <avtikhon@tarantool.org>]

Hi, thanks for the patch, as I see no new degradation found in
gitlab-ci testing commit criteria pipeline [1], patch LGTM.

[1] - https://gitlab.com/tarantool/tarantool/-/pipelines/222853269

On Sat, Oct 31, 2020 at 07:29:11PM +0300, sergos@tarantool.org wrote:
> From: Sergey Ostanevich <sergos@tarantool.org>
> 
> Hi!
> 
> Thanks to Oleg Babin's comment I found there's no need to update any lua
> interfaces, since the reason was in C implementation. Also, there is one
> place the change is played, so after I fixed it I got complete testing 
> pass. 
> Force-pushed branch, v2 patch attached.
> 
> 
> 
> Before this patch fiber.cond():wait() just returns for cancelled
> fiber. In contrast fiber.channel():get() threw "fiber is
> canceled" error.
> This patch unify behaviour of channels and condvars and also fixes
> related net.box module problem - it was impossible to interrupt
> net.box call with fiber.cancel because it used fiber.cond under
> the hood. Test cases for both bugs are added.
> 
> Closes #4834
> Closes #5013
> 
> Co-authored-by: Oleg Babin <olegrok@tarantool.org>
> 
> @TarantoolBot document
> Title: fiber.cond():wait() throws if fiber is cancelled
> 
> Currently fiber.cond():wait() throws an error if waiting fiber is
> cancelled like in case with fiber.channel():get().
> ---
> 
> Github: https://gitlab.com/tarantool/tarantool/-/commits/sergos/gh-5013-fiber-cond                                                                                                                          
> Issue: https://github.com/tarantool/tarantool/issues/5013                                                                                                                                                   
> 
>  src/box/box.cc                                |  6 +-
>  src/lib/core/fiber_cond.c                     |  1 +
>  test/app-tap/gh-5013-fiber-cancel.test.lua    | 23 +++++++
>  test/box/net.box_fiber_cancel_gh-4834.result  | 65 +++++++++++++++++++
>  .../box/net.box_fiber_cancel_gh-4834.test.lua | 29 +++++++++
>  5 files changed, 120 insertions(+), 4 deletions(-)
>  create mode 100755 test/app-tap/gh-5013-fiber-cancel.test.lua
>  create mode 100644 test/box/net.box_fiber_cancel_gh-4834.result
>  create mode 100644 test/box/net.box_fiber_cancel_gh-4834.test.lua
> 
> diff --git a/src/box/box.cc b/src/box/box.cc
> index 18568df3b..bfa1051f9 100644
> --- a/src/box/box.cc
> +++ b/src/box/box.cc
> @@ -305,10 +305,8 @@ box_wait_ro(bool ro, double timeout)
>  {
>  	double deadline = ev_monotonic_now(loop()) + timeout;
>  	while (is_box_configured == false || box_is_ro() != ro) {
> -		if (fiber_cond_wait_deadline(&ro_cond, deadline) != 0)
> -			return -1;
> -		if (fiber_is_cancelled()) {
> -			diag_set(FiberIsCancelled);
> +		if (fiber_cond_wait_deadline(&ro_cond, deadline) != 0) {
> +                        if (fiber_is_cancelled()) diag_set(FiberIsCancelled);
>  			return -1;
>  		}
>  	}
> diff --git a/src/lib/core/fiber_cond.c b/src/lib/core/fiber_cond.c
> index 904a350d9..b0645069e 100644
> --- a/src/lib/core/fiber_cond.c
> +++ b/src/lib/core/fiber_cond.c
> @@ -108,6 +108,7 @@ fiber_cond_wait_timeout(struct fiber_cond *c, double timeout)
>  		diag_set(TimedOut);
>  		return -1;
>  	}
> +	if (fiber_is_cancelled()) return -1;
>  	return 0;
>  }
>  
> diff --git a/test/app-tap/gh-5013-fiber-cancel.test.lua b/test/app-tap/gh-5013-fiber-cancel.test.lua
> new file mode 100755
> index 000000000..ae805c5bf
> --- /dev/null
> +++ b/test/app-tap/gh-5013-fiber-cancel.test.lua
> @@ -0,0 +1,23 @@
> +#!/usr/bin/env tarantool
> +
> +local tap = require('tap')
> +local fiber = require('fiber')
> +local test = tap.test("gh-5013-fiber-cancel")
> +
> +test:plan(2)
> +
> +local result = {}
> +
> +function test_f()
> +    local cond = fiber.cond() 
> +    local res, err = pcall(cond.wait, cond) 
> +    result.res = res
> +    result.err = err
> +end
> +
> +local f = fiber.create(test_f)
> +f:cancel()
> +fiber.yield()
> +
> +test:ok(result.res == false, tostring(result.res))
> +test:ok(tostring(result.err) == 'fiber is cancelled', tostring(result.err))
> diff --git a/test/box/net.box_fiber_cancel_gh-4834.result b/test/box/net.box_fiber_cancel_gh-4834.result
> new file mode 100644
> index 000000000..eab0a5e4d
> --- /dev/null
> +++ b/test/box/net.box_fiber_cancel_gh-4834.result
> @@ -0,0 +1,65 @@
> +-- test-run result file version 2
> +remote = require 'net.box'
> + | ---
> + | ...
> +fiber = require 'fiber'
> + | ---
> + | ...
> +test_run = require('test_run').new()
> + | ---
> + | ...
> +
> +-- #4834: Cancelling fiber doesn't interrupt netbox operations
> +function infinite_call() fiber.channel(1):get() end
> + | ---
> + | ...
> +box.schema.func.create('infinite_call')
> + | ---
> + | ...
> +box.schema.user.grant('guest', 'execute', 'function', 'infinite_call')
> + | ---
> + | ...
> +
> +error_msg = nil
> + | ---
> + | ...
> +test_run:cmd("setopt delimiter ';'")
> + | ---
> + | - true
> + | ...
> +function gh4834()
> +    local cn = remote.connect(box.cfg.listen)
> +    local f = fiber.new(function()
> +        _, error_msg = pcall(cn.call, cn, 'infinite_call')
> +    end)
> +    f:set_joinable(true)
> +    fiber.yield()
> +    f:cancel()
> +    f:join()
> +    cn:close()
> +end;
> + | ---
> + | ...
> +test_run:cmd("setopt delimiter ''");
> + | ---
> + | - true
> + | ...
> +gh4834()
> + | ---
> + | ...
> +error_msg
> + | ---
> + | - fiber is cancelled
> + | ...
> +box.schema.func.drop('infinite_call')
> + | ---
> + | ...
> +infinite_call = nil
> + | ---
> + | ...
> +channel = nil
> + | ---
> + | ...
> +error_msg = nil
> + | ---
> + | ...
> diff --git a/test/box/net.box_fiber_cancel_gh-4834.test.lua b/test/box/net.box_fiber_cancel_gh-4834.test.lua
> new file mode 100644
> index 000000000..06fb3ceac
> --- /dev/null
> +++ b/test/box/net.box_fiber_cancel_gh-4834.test.lua
> @@ -0,0 +1,29 @@
> +remote = require 'net.box'
> +fiber = require 'fiber'
> +test_run = require('test_run').new()
> +
> +-- #4834: Cancelling fiber doesn't interrupt netbox operations
> +function infinite_call() fiber.channel(1):get() end
> +box.schema.func.create('infinite_call')
> +box.schema.user.grant('guest', 'execute', 'function', 'infinite_call')
> +
> +error_msg = nil
> +test_run:cmd("setopt delimiter ';'")
> +function gh4834()
> +    local cn = remote.connect(box.cfg.listen)
> +    local f = fiber.new(function()
> +        _, error_msg = pcall(cn.call, cn, 'infinite_call')
> +    end)
> +    f:set_joinable(true)
> +    fiber.yield()
> +    f:cancel()
> +    f:join()
> +    cn:close()
> +end;
> +test_run:cmd("setopt delimiter ''");
> +gh4834()
> +error_msg
> +box.schema.func.drop('infinite_call')
> +infinite_call = nil
> +channel = nil
> +error_msg = nil
> -- 
> 2.17.1
>