On Oct 5, 2012, at 12:35 PM, Felix Meschberger wrote: > Hi, > > Am 03.10.2012 um 19:28 schrieb David Jencks: > >> I've had several ideas about DS enhancements, some of which I've >> implemented, and would like some feedback about how desirable they are >> before committing or proceeding with them. >> >> 1. (FELIX-3692) If you manually enable/disable components some of the work >> gets done asynchronously. I propose an api for finding out whether this >> work is done or waiting for it, something like >> >> boolean tasksCompleted(); >> >> void waitForTasksCompleted(); >> >> >> on ScrService. (suggestions for better names welcome :-) One use would be >> in our tests to replace the delay() call. > > -1 > > I think such information is without any value. And our own tests being the > sole use cases is a bit weak to add API.
The use cases I have are: 1. shutdown. We want to make sure the queue is empty before turning off logging. (FELIX-3704) 2. You might want to install a lot of application deployer components and make sure they are all fully started before starting say a file listener that looks for applications to deploy. If some of the first set of components are enabled through code, it's hard to tell if they are all completely started without knowing exactly what they are. Similarly you might want to know if a server is "fully started", i.e. all the components that are enabled have at least tried to activate. I'm not 100% sure this is a good idea, but I think it could have some use. > >> >> 2. (FELIX-3557) There are several circumstances in which, as the spec >> warns, you can't establish a circular dependency between components. In >> some of these cases, the order in which the components are activated >> determines whether all the references are established. This is hard to >> understand from a users point of view :-). Sometimes it's possible to >> detect these situations and establish the reference asynchronously. The >> patch attached to the issue does this but needs a little more work to only >> try with services from DS components. > > If I understand the issue/patch correctly, it does something like this: If an > optional service cannot be eagerly bound (to call a bind method taking the > service instance) due to a circularity (exception thrown from the > BundleContext.getService method) it will not be bound but may later be bound > if the actual service instance is created. Correct ? > > I think, this sounds good. OK, I'll commit it. > >> >> For these two, I'm wondering if they would be useful enough to propose for >> the DS 1.3 spec. > > Does FELIX-3557 really imply a spec change ? At most it might be kind of an > implementation hint. If you don't think it needs a spec change I won't worry. > >> >> 3. (re-proposal) I'd like to propose moving the implementation to java 5 >> again with generics etc. The last time I suggested this there was a lot of >> pushback on the grounds that there are a lot of people using DS on limited >> platforms. However, none of these alleged :-) people is using trunk, >> because for several months the classes pulled from the concurrent library >> were wrong and trunk just didn't run on pre-java-5 vms. Are the compendium >> 4.3 spec classes we pull in even compatible with pre-java-5 vms? > > The longer I think about it, the more I have to admit that I agree.... I'm going to change this now because it will make some refactoring easier. If people don't like it we can change back after I'm done. > >> >> 4. (radical idea I haven't tried yet) I'm becoming increasingly convinced >> that the state objects in AbstractComponentManager mostly cause confusion >> and make the code more complicated and less reliable. > > Well, these objects have been quite simple and easy to understand and worked > perfectly (admittedly with some glitches). Now over time and patches applied, > I agree they became quite complex and the concurrency behaviour became more > complex. So for concurrency having immutable objects is a lot easier to > handle than mutable ones. > >> The spec really only describes two states, enabled and disabled. The >> variations on enabled -- whether the component has all its dependencies >> satisfied, whether the service is registered, whether there are any >> implementation objects created -- all seem somewhat orthogonal and depend >> very much on the environment and don't seem to relate well to a single >> "dimension" of state. I'm considering trying to refactor the code that >> responds to outside actions (activate/deactivate and dependencies >> appearing/disappearing) to be more "straight-through" with checks on the >> specific aspects of state that they need. Possibly we would want to put the >> "dynamic state" such as dependencies + instances in a single state object, >> but this is a different approach to the current state objects which have no >> internal state. > > I agree, that the states enabled and disabled might be confusing. But I am > not sure, whether those are really states of component instances (or > component configurations as the spec calls them). Rather they are states of > the "abstract" component. > > The component instances on the other hand have states like unsatisfied, > activating, active, registered, etc. > > In our implementation the component instance is represented by the > AbstractComponentManager and its extensions while the "abstract" component is > represented by combination of the ComponentHolder and the ComponentMetadata. I'm going to think about this some more and try some experiments. thanks for the comments! david jencks > > Regards > Felix
