Run the handlers for replication commands as background processes. This should
improve the visibility in our metrics, and reduce the number of "running db
transaction from sentinel context" warnings.
Ideally it means converting the things that fire off deferreds into the night
into things that actually return a Deferred when they are done. I've made a bit
of a stab at this, but it will probably be leaky.
(instead of everywhere that writes a response. Or rather, the subset of places
which write responses where we haven't forgotten it).
This also means that we don't have to have the mysterious version_string
attribute in anything with a request handler.
Unfortunately it does mean that we have to pass the version string wherever we
instantiate a SynapseSite, which has been c&ped 150 times, but that is code
that ought to be cleaned up anyway really.
While I was going through uses of preserve_fn for other PRs, I converted places
which only use the wrapped function once to use run_in_background, to avoid
creating the function object.
There were a bunch of places where we fire off a process to happen in the
background, but don't have any exception handling on it - instead relying on
the unhandled error being logged when the relevent deferred gets
garbage-collected.
This is unsatisfactory for a number of reasons:
- logging on garbage collection is best-effort and may happen some time after
the error, if at all
- it can be hard to figure out where the error actually happened.
- it is logged as a scary CRITICAL error which (a) I always forget to grep for
and (b) it's not really CRITICAL if a background process we don't care about
fails.
So this is an attempt to add exception handling to everything we fire off into
the background.
This fixes a class of 'Unexpected logcontext' messages, which were happening
because the logcontext was somewhat arbitrarily swapping between the sentinel
and the `run` logcontext.
The empty string is a valid setting for the bind_address option, so
explicitly check for None here instead.
Signed-off-by: Johannes Löthberg <johannes@kyriasis.com>
Some streams will occaisonally advance their positions without actually
having any new rows to send over federation. Currently this means that
the token will not advance on the workers, leading to them repeatedly
sending a slightly out of date token. This in turns requires the master
to hit the DB to check if there are any new rows, rather than hitting
the no op logic where we check if the given token matches the current
token.
This commit changes the API to always return an entry if the position
for a stream has changed, allowing workers to advance their tokens
correctly.
