Initial reason for the change is doing "attributeWhenReady" on boolean sensor with "false" as the expected value. That blocks indefinitely with the current implementation.
Using an enricher wouldn't allow for customizing the timeout - currently "indefinite" when starting and 1 min when stopping. We could extend "attributeWhenReady" with a timeout argument only (if needed) and defer the rest to an enricher. As for "option 2" we could fix it in a backwards compatible way: * introduce "attributeWhenTruthy", alias to "attributeWhenReady" * introduce "attributeWhenPresent" with a notNull && notEmpty check * deprecate "attributeWhenReady" Svet. > On 7.08.2016 г., at 15:03, Alex Heneveld <[email protected]> > wrote: > > You could add an isSet enricher then wait on it. I prefer customisation in > enrichers rather than extending the dsl. > > What is the use case? Everywhere I've seen whenReady is the most natural. > > Best > Alex > > On 5 Aug 2016 17:07, "Aled Sage" <[email protected]> wrote: > >> Hi all, >> >> Motivated by Andrew's recent PR [1] and Svet's suggestion, I'd like to >> propose a change to the semantics/arguments to >> $brooklyn:attributeWhenReady(). >> >> _*Current Behaviour*_ >> >> _Simple example_ >> If you write in a YAML blueprint something like: >> >> brooklyn.config: >> myurl: $brooklyn:component("db").attributeWhenReady("datastore.url") >> >> then when you attempt to get the config value for "myurl" it will block >> until the "datastore.url" sensor value is available on the entity with id >> "db". >> >> _"Groovy truth" example_ >> The attributeWhenReady actually blocks until groovy truth is satisfied >> (boolean is true, collection is non-empty, string is non-empty, etc). >> >> You can therefore write: >> >> brooklyn.config: >> launch.latch: >> $brooklyn:component("db").attributeWhenReady("service.isUp") >> >> and it will block until the db entity's service.isUp sensor is true. >> >> Unfortunately this means it's impossible to wait for a boolean attribute >> to be non-null (i.e. stop waiting when false or true). >> >> _Java API Functionality_ >> Comparing the yaml DSL with what can be done in DependentConfiguration >> [2], there is a lot we can't do: >> >> * customize the "readiness" function (i.e. what sensor values mean >> "ready") >> * define "abort conditions" (e.g. stop waiting if the entity >> transitions to some other state) >> * specify a timeout >> * give a default value for if there is a timeout, or if the entity is >> removed while we're waiting. >> >> >> _*Proposal: option 1*_ >> >> My favoured option is to make attributeWhenReady more configurable. >> >> For example, we could support: >> >> brooklyn.config: >> launch.latch: $brooklyn:component("db").attributeWhenReady: >> sensor: "service.isUp" >> readiness: $brooklyn:predicates.equalTo("true") >> timeout: 10m >> >> Maybe we'd support overloading of in-lining the args (relying on parameter >> order of [sensor, readiness, timeout]), such as: >> >> brooklyn.config: >> launch.latch: >> $brooklyn:component("db").attributeWhenReady("service.isUp", >> $brooklyn:predicates.equalTo("true"), 10m) >> >> I think I'm ok with leaving the default as groovy-truth semantics, as long >> as we make the documentation clearer for that. >> >> However, this proposal might well be hard to implement. It would likely >> require significant change to how we parse the $brooklyn expressions (if my >> recollection of this code is correct). >> >> _*Proposal: option 2*_ >> >> An alternative suggested by Svet in a comment on [1]: >> >> Should we fix attributeWhenReady instead? It's confusing to have it >> wait indefinitely on false. >> Having another attribute, very similar to attributeWhenReady >> complicates things even further. >> >> Suggest renaming attributeWhenRedy to attributeWhenTruth and >> changing attributeWhenReady to wait on notNull && notEmpty. >> >> That sounds like a good idea - it feels much more explicit, and is very >> simple to implement. >> >> However, it would break backwards compatibility (e.g. for those using >> `attributeWhenReady("service.isUp")`. >> >> If we think the semantics are wrong, then we should definitely change it >> while we're still on version 0.x rather than ignoring it. >> >> Aled >> >> [1] https://github.com/apache/brooklyn-server/pull/282 >> [2] https://github.com/apache/brooklyn-server/blob/rel/apache- >> brooklyn-0.9.0/core/src/main/java/org/apache/brooklyn/core/ >> sensor/DependentConfiguration.java#L669 >> >>
