The database settings could also be overridden in the configuration file
besides the command line.
We should therefore pass the path to the runtime configuration file, so
the Alembic process can initialize its configuration from the same file
and use the same settings.
If the path of the default database engine is overridden via `--workdir`
option then it won't be visible to the new `python` subprocess spawned
for Alembic.
We should load the latest timestamps from the db when the thread starts
instead of doing it in the constructor.
The constructor may be invoked when the entities engine hasn't been
initialized yet, and result in deadlocks.
The `variable` plugin may break in the constructor the first time the
application is started.
That's because it tries to initialize the cache of stored variables, but
the local database hasn't yet been initialized.
That's because plugins are registered _before_ the entities engine is
initialized, as the entities engine assumes that it already has plugins
to scan for entities.
Therefore, the initialization of the `variable` plugin's cache should be
lazy (only done upon the first call to `get`/`set` etc.), in order to
prevent deadlock situations where the plugin waits for the engine to
start, but the engine will be initialized only after the plugin is
ready.
And the lazy initialization logic should also ensure that the entities
engine has been properly started (and emit a `TimeoutError` if that's
not the case), in order to prevent race conditions.
- If a Python optional dependency is available as a system package on
the target system, try and install it that route rather than pip. It's
usually faster and it decreases the risk of breaking system packages.
- Added support for apk dependencies in manifest files. This brings the
number of distros officially supported by all the extensions to four:
- Alpine
- Arch
- Debian
- Ubuntu
The Tornado WSGI container won't guarantee the termination of the
spawned workers upon termination, so the code of the backend has to take
care of it and terminate all the children processes of the server
process when it terminates.
This also means that `psutil` is now a required base dependency, as we
need to expand the process subtree under the webserver launcher.