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

[Sergey Ostanevich <sergos@tarantool.org>]

Sorry, the patch was not updated. Here’s a new one and the branch is updated

commit 42ea06f7cf69ee6b492cefcbb201bc9bba15c686
Author: Sergey Ostanevich <sergos@tarantool.org>
Date:   Tue Nov 3 12:52:26 2020 +0300

    core: handle fiber cancellation for fiber.cond
    
    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.

---

Github: https://gitlab.com/tarantool/tarantool/-/commits/sergos/gh-5013-fiber-cond
Issue: https://github.com/tarantool/tarantool/issues/5013

@Changelog
* fiber.cond().wait() now throws if fiber is cancelled

diff --git a/src/box/box.cc b/src/box/box.cc
index 18568df3b..29f74e94b 100644
--- a/src/box/box.cc
+++ b/src/box/box.cc
@@ -305,10 +305,9 @@ 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..cc59eaafb 100644
--- a/src/lib/core/fiber_cond.c
+++ b/src/lib/core/fiber_cond.c
@@ -108,6 +108,11 @@ fiber_cond_wait_timeout(struct fiber_cond *c, double timeout)
 		diag_set(TimedOut);
 		return -1;
 	}
+	if (fiber_is_cancelled()) {
+		if (diag_is_empty(diag_get()))
+                        diag_set(FiberIsCancelled);
+		return -1;
+	}
 	return 0;
 }
 
diff --git a/src/lib/core/fiber_cond.h b/src/lib/core/fiber_cond.h
index 87c6f2ca2..2662e0654 100644
--- a/src/lib/core/fiber_cond.h
+++ b/src/lib/core/fiber_cond.h
@@ -114,7 +114,7 @@ fiber_cond_broadcast(struct fiber_cond *cond);
  * @param cond condition
  * @param timeout timeout in seconds
  * @retval 0 on fiber_cond_signal() call or a spurious wake up
- * @retval -1 on timeout, diag is set to TimedOut
+ * @retval -1 on timeout or fiber cancellation, diag is set
  */
 int
 fiber_cond_wait_timeout(struct fiber_cond *cond, double timeout);
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..ca4ca2c90
--- /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, 'expected result is false')
+test:ok(tostring(result.err) == 'fiber is cancelled', 'fiber cancellation should be reported')
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..4ed04bb61
--- /dev/null
+++ b/test/box/net.box_fiber_cancel_gh-4834.result
@@ -0,0 +1,62 @@
+-- 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 netbox_runner()
+    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
+ | ...
+netbox_runner()
+ | ---
+ | ...
+error_msg
+ | ---
+ | - fiber is cancelled
+ | ...
+box.schema.func.drop('infinite_call')
+ | ---
+ | ...
+infinite_call = 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..bc0e5af6e
--- /dev/null
+++ b/test/box/net.box_fiber_cancel_gh-4834.test.lua
@@ -0,0 +1,28 @@
+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 netbox_runner()
+    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 ''");
+netbox_runner()
+error_msg
+box.schema.func.drop('infinite_call')
+infinite_call = nil
+error_msg = nil

======================

> On 11 Nov 2020, at 00:16, Sergey Ostanevich <sergos@tarantool.org> wrote:
> 
> Hi Leonid, thank you for the review!
> 
> I put two parts together to handle them in one patch.
> 
>> On 4 Nov 2020, at 13:00, Leonid Vasiliev <lvasiliev@tarantool.org> wrote:
>> 
>> Hi! Thank you for the patch.
>> See some comments below:
>> 
>> 1) The patch changes undocumented behavior, AFAIU.
>> So, I have a question:"Do you plan to backport the patch to
>> tarantool 1.10?". If the answer is "Yes" - I'm comfortable with the
>> changes. But if the answer is "No" - I will object, because in this case
>> both behaviors must be supported in all modules.
>> 
> 
> Yes, the plan is to push it down to 1.10
> 
>> 2) I think changing the behavior in C doesn't cause much of a problem,
>> because before when you wait without timeout, you don't need to check
>> the return value (it's always 0). But in Lua it will cause the problems,
>> because now throws an error if cancelled and all wait calls should be
>> wrapped to pcall.
> 
> Exactly it is the change to Lua and we intentionally make it, since original
> behaviour is wrong. Good things are: fiber.cond has no big presence in the
> /tarantool sourcebase and the cancellation of fiber itself means the fiber
> has to quit.
> 
>> 
>> On 31.10.2020 19:29, 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
>> 
>> 3) behaviour -> behavior.
> 
> Depends on spellchecker - mine sets it to this British version.
> 
>> 
>>> 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().
>> 
>> 4) I don't think it's a good decision adding a comparison with
>> fiber.channel():get() to the documentation. Up to you.
>> 
> 
> I’d agree to you: let’s just put the new behaviour here.
> 
>> 5) Document the changes in module.h.
> 
> Done (need to rebuild, obviously).
> 
>> 
>>> ---
>> 
>> 6) Add @ChangeLog.
>> 
>>> 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..9e824453d 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);
>> 
>> 7) According to https://www.tarantool.io/en/doc/latest/dev_guide/c_style_guide/
>> it's seems like you are trying to hide something)
>> Use:
>> ```
>> if (condition)
>>   action();
>> ```
>> Instead of:
>> ```
>> if (condition) action();
>> another_action();
>> ```
> 
> Fixed.
> 
>>> 			return -1;
>>> 		}
>>> 	}
>>> diff --git a/src/lib/core/fiber_cond.c b/src/lib/core/fiber_cond.c
>>> index 904a350d9..0c93c5842 100644
>>> --- a/src/lib/core/fiber_cond.c
>>> +++ b/src/lib/core/fiber_cond.c
>>> @@ -108,6 +108,10 @@ fiber_cond_wait_timeout(struct fiber_cond *c, double timeout)
>>> 		diag_set(TimedOut);
>>> 		return -1;
>>> 	}
>>> +	if (fiber_is_cancelled()) {
>>> +		if (diag_is_empty(diag_get())) diag_set(FiberIsCancelled);
>> 
>> 8) The same as previously:
>> ```
>> if (condition)
>>   action();
>> ```
>> 
> 
> Fixed.
> 
>> 9) Checking diag on empty looks strange to me. I think we should add an
>> error to diag without this check. If we want to save the previous error,
>> I suggest to use the stack diag.
> 
> I made this because this interface is used inside the testing machinery, where 
> exact cause of e.g. replica disconnection is reported. If we put the diag here
> unconditionally it will break this use of diag. I believe the stack diag also 
> is not supported there yet.
> 
> 
>>> +		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))
>> 
>> 10) Use a user-frendly check message (in both checks).
>> 
> Fixed
> 
>>> 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()
>> 
>> 11) I think this is not a self-documenting name for the function.
>> 
> Renamed.
> 
>>> +    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
>> 
>> 12) You didn't introduce the variable "channel". In addition, I looked
>> at a couple of tests and didn't see them cleaning up variables. But I
>> don't mind.
>> 
> Removed this one. In general, clean up prevents flaky.
> 
>>> +error_msg = nil
> 
> =================
> 
> 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.
> ---
> 
> Github: https://gitlab.com/tarantool/tarantool/-/commits/sergos/gh-5013-fiber-cond
> Issue: https://github.com/tarantool/tarantool/issues/5013
> 
> @Changelog
> * fiber.cond().wait() now throws if fiber is cancelled
> 
> src/box/box.cc                                |  6 +-
> src/lib/core/fiber_cond.c                     |  4 ++
> 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, 123 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..9e824453d 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..0c93c5842 100644
> --- a/src/lib/core/fiber_cond.c
> +++ b/src/lib/core/fiber_cond.c
> @@ -108,6 +108,10 @@ fiber_cond_wait_timeout(struct fiber_cond *c, double timeout)
>                diag_set(TimedOut);
>                return -1;
>        }
> +       if (fiber_is_cancelled()) {
> +               if (diag_is_empty(diag_get())) diag_set(FiberIsCancelled);
> +               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..34711fb31
> --- /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
> -- 
> 2.29.2