lua: shutdown tasks worker fiber

As this fiber is made system in the commit bf620650 ("box: finish
client fibers on shutdown") we don not need the existing protection from
cancelling. So first remove it. Now make it managed on shutdown.

Note that we may have issues as we finish this fiber too early. The
tasks scheduled but not executed at this moment will never be executed.
So the tasks that be scheduled after fiber is finished. Now when we
don't use worker fiber for swim gc this will not cause leaks. And
leaking fd on Tarantool shutdown in fio is not a problem.

Closes #9722

NO_CHANGELOG=internal
NO_DOC=internal

src/lua/fiber.c

@@ -922,6 +922,7 @@ lbox_fiber_stall(struct lua_State *L)
 {
 	(void) L;
 	fiber_yield();
+	luaL_testcancel(L);
 	return 0;
 }
 

src/lua/fiber.lua

@@ -100,25 +100,16 @@ local function worker_f()
             stall()
         end
         worker_next_task = task.next
-        task.f(task.arg)
+        pcall(task.f, task.arg)
         fiber.sleep(0)
     end
 end
 
 local worker_name = 'tasks_worker_fiber'
 
-local function worker_safe_f()
-    pcall(worker_f)
-    -- Worker_f never returns. If the execution is here, this
-    -- fiber is probably canceled and now is not able to sleep.
-    -- Create a new one.
-    worker_fiber = fiber.new(worker_safe_f)
-    fiber_set_system(worker_fiber)
-    worker_fiber:name(worker_name)
-end
-
-worker_fiber = fiber.new(worker_safe_f)
+worker_fiber = fiber.new(worker_f)
 fiber_set_system(worker_fiber)
+fiber_set_managed_shutdown(worker_fiber)
 worker_fiber:name(worker_name)
 
 local function worker_schedule_task(f, arg)
@@ -129,7 +120,10 @@ local function worker_schedule_task(f, arg)
         worker_last_task.next = task
     end
     worker_last_task = task
-    worker_fiber:wakeup()
+    -- Fiber is finished on shutdown as it has managed shutdown.
+    if worker_fiber:status() ~= 'dead' then
+        worker_fiber:wakeup()
+    end
 end
 
 -- Start from '_' to hide it from auto completion.

test/app/fiber.result

@@ -1589,7 +1589,6 @@ function task_f(arg)
     if arg <= 3 then                                                            \
         fiber._internal.schedule_task(task_f, arg)                              \
     else                                                                        \
-        fiber.self():cancel()                                                   \
         error('Worker is broken')                                               \
     end                                                                         \
 end

test/app/fiber.test.lua

@@ -712,7 +712,6 @@ function task_f(arg)
     if arg <= 3 then                                                            \
         fiber._internal.schedule_task(task_f, arg)                              \
     else                                                                        \
-        fiber.self():cancel()                                                   \
         error('Worker is broken')                                               \
     end                                                                         \
 end