api: fix INIT state stuck

[DerekBum]

Sometimes, instance could enter the queue initialization while still not running (for example, left in the orphan mode). This resulted in "lazy start". But Tarantool does not call box.cfg {} after leaving orphan mode, so queue could stuck in the INIT state.

Now if the instance is read-only, separate fiber is watching for updates of its mode.

Note that this fix works only for Tarantool versions >= 2.10.0. This is because of used watchers.

Closes #226

[oleg-jukovec]

Is there a reason to block queue_init() until orphan mode switched? The wait and the queue initialization could be done in a background as it is done by box.cfg wrapper now.

[DerekBum]

The wait and the queue initialization could be done in a background as it is done by box.cfg wrapper now.

Tarantool does not call box.cfg {} upon exiting the orphan mode. Or are you suggesting to run a fiber in a background, that will check status of the instance. And if the orphan mode changes, it updates the status?

[oleg-jukovec]

The wait and the queue initialization could be done in a background as it is done by box.cfg wrapper now.

Tarantool does not call box.cfg {} upon exiting the orphan mode. Or are you suggesting to run a fiber in a background, that will check status of the instance. And if the orphan mode changes, it updates the status?

Yes, it is. When the status check will success - initialize the instance in a background.

[DerekBum]

Updated the code. Now watcher is run in a different fiber, without blocking init function. Note that now this fix only works for Tarantool versions >= 2.10.0. On newer versions this bug will still be present.

[0x501D]

LGTM