Document that fiber.yield and fiber.sleep may raise an exception

[RunsFor]

There is a frequent misunderstanding in tarantool community with how fiber.yield, fiber.testcancel and fiber.cancel works. I believe it happens, because documentation says nothing about yield and sleep may actually raise an exception. This may form wrong assumptions about how fiber model works.

I suggest add an "exception" section to yield and sleep functions documentation. Some examples would be nice to have.

[pgulutzan]

I will add this in section "Module fiber" if nobody objects in the next few days.

Warning: yield() and sleep() can fail (raise an exception).
For example, this function has a loop which repeats until cancel() happens.
The last thing that it will print is 'before yield', which demonstrates
that yield() failed, the loop did not continue until testancel() failed.
fiber = require('fiber')
function function_name()
while true do
print('before testcancel')
fiber.testcancel()
print('before yield')
fiber.yield()
end
end
fiber_object = fiber.create(function_name)
fiber.sleep(.1)
fiber_object:cancel()

[olegrok]

But no only yield and sleep could raise. All operations that yield implicitly could raise such error as well.

[RunsFor]

I will add this in section "Module fiber" if nobody objects in the next few days.

I would also point it out in the function documentation in "Exception" section. As an example, fiber.kill has such section.