I am continually tempted to implement lifecycle control into coinjema - ie,the ability to throw in annotations to your classes that allow coinjema to notify your objects of various lifecycle events - creation, finalization, etc. But, I'm resisting the urge because I think it's a problematic idea in the long run. I'm already noticing problems that happen when I get too aggressive about calling initialization routines in my constructors or dependency injection methods. Often times, this results in problems with circular dependencies - specifically when dynamic dependencies are mixed with static. If I could resolve that, some of these lifecycle issues would go away I think.
JavaSpace ContextSource. Ie, store configuration data in a JavaSpaces service and let Coinjema automatically retrieve such objects and insert them into your objects. In general I'm thinking a lot about what it might mean/enable if Coinjema were fully jini-capable.
Several times I've run into the situation where I want a property file that
gets default values from a property file in a base context, but overrides just some of the
values in a sub-context. Right now, you'd have to put all the values in every property
file. I get around this currently by having my class depend on two property files, one
which holds the default values and another that holds the overriding values and I call
putAll() on my
Properties object to override the values. A
little kludge that works well provided you only want/need a single default set of
properties and a single overriding set of properties. I'd like to enable full property
value inheritance from context to sub-context.
I've finally started using Coinjema in an actual project, which has helped me find some weaknesses in Coinjema. Most notably, working out circular dependencies. I've also done some work to make Coinjema thread-safe. The result of both of these actions is that Coinjema performance is back in the toilet (after some nice previous improvements in that area). To be specific, object creation is approximately 50 times slower than normal when using Coinjema. performance has since been improved to about 25x slower.
25 times slower looks worse than it actually is. The performance penalty is mostly restricted to object creation, which is a small part of a system's performance to begin with (discounting GC issues, which should not be affected by Coinjema). Creating a normal object and setting a couple of properties takes about 80 nanoseconds on my 1.8ghz centrino laptop, and about 2000 nanoseconds for a Coinjema configured object. There are 1 million nanoseconds in a millisecond - so you'd have to create 1000 objects to decrease your system's performance by ~2 milliseconds. It's a tradeoff that has to be weighed against the advantages. Certainly one wouldn't want DAO objects mapped to database table rows to be Coinjema objects, but it probably wouldn't be too bad to create a new Coinjema object or 3 or 10 for each http request to a servlet engine.
A stickier problem is the issue of thread-safety. I've modified the code to avoid obvious multi-threading problems, but I remain concerned about the possibility of deadlocks if it were used in a heavily multi-threaded environment with very complex circular dependencies. I've not yet devised a test case that reveals such a problem, but I can imagine some that might. This is something I'll have to look into soon. Have since created tests that revealed deadlocks and have reorganied the code to avoid this. A nice benefit was the synchronization plan was greatly simplified and performance enhanced.
I'd like to play with the idea of using Coinjema to intercept calls to getXXX() as opposed to intercepting constructor calls and then configuring the objects at initialization time. There would be three advantages of doing so: Object construction would be quick; objects could be more easily updated at runtime since every call to getXXX() they make would go to Coinjema to retrieve the dependency; and a single object could play in multiple contexts rather than being fixed in a particular context at the moment of its creation. The difficulty is figuring out what the intended context is a the time of the call to getXXX(). This is done and working with the new @CoinjemaDynamic annotation.
Another desirable feature with redirects would be to preserve the original context through the redirect. What this means is, let's say there is the root context:
root singleton.groovy myClass.singleton.redirect (points to "singleton")
And there is a child context:
The point of the singleton.groovy entry in the child context is to supply objects in that context with a separate instance of the singleton class - could be a different implementation, could just be configured differently. The problem here is, which instance of singleton will MyClass get if it is created in the child context? Unfortunately, the answer is it will get the root singleton because as Coinjema searches for the MyClass.singleton dependency, it finds it in the root context, and the redirect therefore only searches the root context. Therefore it is necessary to put another Myclass.singleton.redirect into the child context if it is desired that it find the context specific instance of singleton (which seems like that natural assumption to me). Removing this would remove some duplication in the config files. This is also done now.
Additionally, are both singleton.groovy files really necessary if all they are doing is creating context specific instances of the same class? Why can't there be some way to tell Coinjema that the root config file should be duplicated internally for each child context that doesn't override it? This also would greatly reduce the number of config files I have for my system, and I suspect for many others. Maybe a new file format ".instance" is needed to allow one to specify a class name that will be created for each context. This issue is thornier than expected, but also partially mitigated by the new dynamic dependencies and more targeted context tracking mechanism which allows a single shared service object to behave differently in different call contexts.