Introduce `Clock.call_when_running(...)` to wrap startup code in a
logcontext, ensuring we can identify which server generated the logs.
Background:
> Ideally, nothing from the Synapse homeserver would be logged against the `sentinel`
> logcontext as we want to know which server the logs came from. In practice, this is not
> always the case yet especially outside of request handling.
>
> Global things outside of Synapse (e.g. Twisted reactor code) should run in the
> `sentinel` logcontext. It's only when it calls into application code that a logcontext
> gets activated. This means the reactor should be started in the `sentinel` logcontext,
> and any time an awaitable yields control back to the reactor, it should reset the
> logcontext to be the `sentinel` logcontext. This is important to avoid leaking the
> current logcontext to the reactor (which would then get picked up and associated with
> the next thing the reactor does).
>
> *-- `docs/log_contexts.md`
Also adds a lint to prefer `Clock.call_when_running(...)` over
`reactor.callWhenRunning(...)`
Part of https://github.com/element-hq/synapse/issues/18905
This small PR migrates from `unittest.assertEquals` to
`unittest.assertEqual` which is deprecated from Python2.7:
```python
DeprecationWarning: Please use assertEqual instead.
```
Signed-off-by: Emmanuel Ferdman <emmanuelferdman@gmail.com>
Currently, when a new scheduled task is added and its scheduled time has
already passed, we set it to ACTIVE. This is problematic, because it
means it will jump the queue ahead of all other SCHEDULED tasks;
furthermore, if the Synapse process gets restarted, it will jump ahead
of any ACTIVE tasks which have been started but are taking a while to
run.
Instead, we leave it set to SCHEDULED, but kick off a call to
`_launch_scheduled_tasks`, which will decide if we actually have
capacity to start a new task, and start the newly-added task if so.
During the migration the automated script to update the copyright
headers accidentally got rid of some of the existing copyright lines.
Reinstate them.
