The temporal dependency handler

Regular service dependencies participate to the instance lifecycle. Moreover, the injected service object is either available or not available. A temporal dependency handler is a little different and provides a different resolution pattern. Indeed, the temporal dependency does not invalidate the instance. Moreover, if not available, the temporal dependency waits (and so blocks the current thread) for a provider. Of course, the maximum waiting time can be specified. If a timeout occurs, the handler throws a runtime exception.

Using the handler

First of all, you need to configure the component type to use the handler such as:

<iPOJO xmlns:temporal="org.apache.felix.ipojo.handler.temporal">
	<component
		className="org.apache.felix.ipojo.example.Temporal">
		
                <!-—Temporal dependency configuration -->
		<temporal:requires field="mytemporal"
                />
	<provides />
	</component>
</iPOJO>

Notice that, this handler is an external handler. So, it uses the "org.apache.felix.ipojo.handler.temporal" namespace.
Once described, you can implement your component. The specified field will be mapped to the temporal dependency. As for regular field injection, aggregation, targeted service specification (i.e. interface) are discovered automatically. Filter, comparator and binding policy are also supported. However, the optional attribute is not supported. In fact, this attribute is meaningless in the case of a temporal dependency.
Using the field in your code will try to find a matching service provider. If a provider is available, the field receives the service object immediately. Else, the thread is stopped and waits for a provider. The default wait time is 3s (you can also specify this time). If no provider is available after this time, the thread throws a RuntimeException. If a provider becomes available during this time, the field receives immediately the value and the execution can continue.

Configuration

The handler has only one mandatory attributes:

Field: the implementation field supporting the dependency

The handler supports on specific optional attributes:

Timeout: the maximum time waited in order to find a provider (default: 3s)

The attribute form regular dependencies are also supported.

Download

The handler is available on the download page.
Sources are available on the Felix trunk at the following location: https://svn.apache.org/repos/asf/felix/trunk/ipojo/temporal.dependency.handler

The temporal dependency handler

Using the handler

Configuration

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