Added lazy service loading mechanism #2
Conversation
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I'd prefer an alternative where a Service can fail to initialize and is simply not added to the Context in that case. That way, you can rely on the fact that all Services that can be obtained from the Context actually work... |
The Plugin annotation now has a "lazy" attribute. If true, the ServiceHelper will not load these services during its first loadServices pass. After loading the non-lazy services, standard calls to the Context's getService(Class) method will check the lazy service list for a matching service, if an implementation was not already loaded. NB: these changes require the Context to maintain a reference to a ServiceHelper. ServiceHelper has a canLoadLazy() flag to determine if it is capable of loading lazy services or not (that is, if loadServices() has already been called or not).
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@dscho, could you clarify your preferences? I'm not sure what you mean about obtaining services that don't work. Right now, lazy or not, if a service fails to initialize it's not accessible via the context. In my mind, if SampleServiceImpl has a dependency that may or may not be on the class path, A lazy service doesn't get added to the ServiceIndex until it's loaded, so I don't think there's any way to perceive failing/unloaded services as available. Since the lazy flag is intended for services that may regularly fail to load, the only behavior change should be delaying error messages until the service is requested, which in many cases will be never. So I think avoiding these error messages is valuable, but I'm happy to hear it if you still think there's a better alternative. |
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closing this PR. Just going to change the output so that when a service fails to load it will be printed as a warning instead of an error, since execution continues, and the stack trace will get logged to debug. |
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Sorry for the delay. It was not clear to me what problem exactly you wanted to solve, and I guess that your change to turn the error into a warning makes it much clearer. Thanks! |
Adds the capacity to mark services as lazy so they won't be loaded during context construction, but can be loaded on demand later.
To test:
This is easiest to see with a Service implementation that will fail when loaded .. e.g. https://github.com/hinerm/bioformats/blob/scifio-master/components/scifio/src/loci/formats/services/LuraWaveServiceImpl.java .. but any service will work as long as it's not a parameter of another class (as parameters will be loaded before the parent class, regardless of whether they are lazy or not)