This more appropriately blocks converging in the engine, since we are
now 1-1 decoupled from the Watch resource. This simplifies resource
writing, and should be more accurate around small converged timeouts.
We don't block in the Worker routine when we are polling, because we
expect to get constant poll events, and we can instead be more careful
about these by looking at CheckApply results.
If we can do this for all resources in the future, it would be
excellent!
I can't guarantee this has a significant effect, but it's likely to add
some efficiency when sending multiple BackPoke's at the same time, so
that erroneous ones can be cancelled out easier.
The mgmt graph depends on state tracking to eliminate redundant pokes.
With the Watch loop now able to produce events quickly, it should no
longer play a part in determining the vertex state. This simplifies the
resource API as well!
This adds rate limiting with the limit and burst meta parameters. The
limits apply to how often the Process check is called. As a result, it
might get called more often than there are Watch events due to possible
Poke/BackPoke events.
This system might need to get rethought in the future depending on its
usefulness.
This patch makes a number of changes in the engine surrounding the
resource API. In particular:
* Cleanup of send/read event.
* Cleanup of DoSend (now Event) in the Watch method.
* Events are now more consistently pointers.
* Exiting within Watch is now done in a single place.
* Multiple incoming events will be combined into a single action.
* Events in flight during an action are played back after CheckApply.
* Addition of Close method to API
This gets things ready for rate limiting and semaphore metaparams!
This allows a resource to use polling instead of the event based
mechanism. This isn't recommended, but it could be useful, and it was
certainly fun to code!
This signals which resources have to run their initial pokes, and
removes the racy retry timer. We actually get a proper signal when
things are running too!
This removes some boilerplate from the Watch methods which can be baked
into the engine instead.
This code should be checked for races and locks to make sure we only
start resources when it makes sense to.
This takes the Converged initialization and Startup patterns that are
common in all resources, and bakes it into the core engine. This way
resource writing is much more concise and there is less boilerplate!
This polishes the password resource so that it can actually avoid
writing the password to disk, and so that the work actually happens in
CheckApply where it can properly interact with the graph. This resource
now re-generates the password when it receives a notification.
The send/recv plumbing has been extended so that receivers can detect
when they're receiving new values. This is particularly important if
they might otherwise not expect those values to change and cache them
for efficiency purposes.
Clearly the use of errgroup is flawed.
1) You can't pass in variables, so this is likely to race.
2) You can't get a set of errors, so this is a bad API.
For the second problem, it would be much more sane to return a multierr
or a list of errors. If there's no fix for the first, I think it should
be removed from the lib.
Resources can send "refresh" notifications along edges. These messages
are sent whenever the upstream (initiating vertex) changes state. When
the changed state propagates downstream, it will be paired with a
refresh flag which can be queried in the CheckApply method of that
resource.
Future work will include a stateful refresh tracking mechanism so that
if a refresh event is generated and not consumed, it will be saved
across an interrupt (shutdown) or a crash so that it can be re-applied
on the subsequent run. This is important because the unapplied refresh
is a form of hysteresis which needs to be tracked and remembered or we
won't be able to determine that the state is wrong!
Still to do:
* Update the autogrouping code to handle the edge notify properties!
* Actually finish the stateful bool code
