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engine: graph, resources: Change Watch to use ctx

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This is a general port. There are many optimizations and cleanups we can
do now that we have a proper context passed in. That's for a future
patch.
This commit is contained in:
James Shubin
2023-08-07 20:17:32 -04:00
parent 53a878bf61
commit 963393e3d9
37 changed files with 139 additions and 130 deletions
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25
docs/resource-guide.md
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@@ -277,7 +277,7 @@ will likely find the state to now be correct.
### Watch
```golang
Watch() error
Watch(ctx context.Context) error
```
`Watch` is a main loop that runs and sends messages when it detects that the
@@ -304,23 +304,25 @@ If the resource is activated in `polling` mode, the `Watch` method will not get
executed. As a result, the resource must still work even if the main loop is not
running.
You must make sure to cleanup any running code or goroutines before Watch exits.
#### Select
The lifetime of most resources `Watch` method should be spent in an infinite
loop that is bounded by a `select` call. The `select` call is the point where
our method hands back control to the engine (and the kernel) so that we can
sleep until something of interest wakes us up. In this loop we must wait until
we get a shutdown event from the engine via the `<-obj.init.Done` channel, which
we get a shutdown event from the engine via the `<-ctx.Done()` channel, which
closes when we'd like to shut everything down. At this point you should cleanup,
and let `Watch` close.
#### Events
If the `<-obj.init.Done` channel closes, we should shutdown our resource. When
When we want to send an event, we use the `Event` helper function. This
automatically marks the resource state as `dirty`. If you're unsure, it's not
harmful to send the event. This will ultimately cause `CheckApply` to run. This
method can block if the resource is being paused.
If the `<-ctx.Done()` channel closes, we should shutdown our resource. When we
want to send an event, we use the `Event` helper function. This automatically
marks the resource state as `dirty`. If you're unsure, it's not harmful to send
the event. This will ultimately cause `CheckApply` to run. This method can block
if the resource is being paused.
#### Startup
@@ -347,7 +349,7 @@ sending out erroneous `Event` messages to keep things alive until it finishes.
```golang
// Watch is the listener and main loop for this resource.
func (obj *FooRes) Watch() error {
func (obj *FooRes) Watch(ctx context.Context) error {
// setup the Foo resource
var err error
if err, obj.foo = OpenFoo(); err != nil {
@@ -371,7 +373,7 @@ func (obj *FooRes) Watch() error {
case err := <-obj.foo.Errors:
return err // will cause a retry or permanent failure
case <-obj.init.Done: // signal for shutdown request
case <-ctx.Done(): // signal for shutdown request
return nil
}
@@ -553,11 +555,6 @@ ready to detect changes.
Event sends an event notifying the engine of a possible state change. It is
only called from within `Watch`.
### Done
Done is a channel that closes when the engine wants us to shutdown. It is only
called from within `Watch`.
### Refresh
Refresh returns whether the resource received a notification. This flag can be