About warming up capsules on backend

[busslina]

Can you suggest a technique to warming up capsules in a backend app?

[GregoryConrad]

Something like the following should work I'd think, but hasn't been tested.

Future<void> main() async {
  final container = CapsuleContainer()..read(aWarmUpCapsule)..read(bWarmUpCapsule);
  await (use(aAsyncCapsule), use(bAsyncCapsule)).wait;
  // do whatever with aCapsule and bCapsule
}

Future<int> aAsyncCapsule(CapsuleHandle use) async => throw 'impl hidden';
Future<bool> bAsyncCapsule(CapsuleHandle use) async => throw 'impl hidden';
AsyncValue<int> aWarmUpCapsule(CapsuleHandle use) => use.future(use(aAsyncCapsule));
AsyncValue<bool> bWarmUpCapsule(CapsuleHandle use) => use.future(use(bAsyncCapsule));
int aCapsule(CapsuleHandle use) => (use(aWarmUpCapsule) as AsyncData).data;
bool bCapsule(CapsuleHandle use) => (use(bWarmUpCapsule) as AsyncData).data;

[GregoryConrad]

If that doesn't work, you can manually create a future and use container.listen on the xyzWarmUpCapsules to set the future as completed once they are an AsyncData.

[busslina]

Seems a cool way !

[GregoryConrad]

Great! Glad to hear it.

[busslina]

Even more refined:

Typedef + extension:

typedef WarmUpCapsulePair<T> = (
  Capsule<Future<T>>,
  Capsule<AsyncValue<T>>,
);

extension WarmUpCapsulePairExtension<T> on WarmUpCapsulePair<T> {
  Future<T> warmUp() {
    cc.read($2);
    return cc.read($1);
  }
}

Capsules:

Future<String> hostnameFutureCapsule(CapsuleHandle use) =>
    use(defaultShellCapsule).hostname();

AsyncValue<String> hostnameAsyncCapsule(CapsuleHandle use) =>
    use.future(use(hostnameFutureCapsule));

String hostnameCapsule(CapsuleHandle use) =>
    use(hostnameAsyncCapsule).data.asNullable()!;

Warm up:

await Future.wait([
        (hostnameFutureCapsule, hostnameAsyncCapsule).warmUp(),
      ]);

[opsb]

It seems a bit awkward that you need to wait on both the warm up and async capsules. Is there an approach where we could mirror the toWarmUpCapsule and only specify the warm up capsules?

[GregoryConrad]

@opsb Sure, you could:

1. Manually create a future (can't remember the Dart API for this since I needed it once, probably some 6 years ago now)
2. container.listen to just the warm up capsules (the ones that return an AsyncValue)
3. Complete the future when all of the warm up capsules are AsyncData. Error the future when any of the capsules are AsyncError

I just never bothered to write that out. If you wanted to add that in a PR along with a test case or two I'd be happy to incorporate it into the framework (the above 3 steps are the proper way to actually warm something up; what I gave before is the "quick and dirty" way to do it in less work).

Could likely be an extension WarmUpCapsuleContainer on CapsuleContainer { Future<void> warmUp<T>(Iterable<Capsule<T>> capsules) => throw 'todo'; }

[busslina]

can't remember the Dart API

https://api.flutter.dev/flutter/dart-async/Completer-class.html