Terminating OSGI blueprint bundle after stop of referenced service

Question

I have such issue. I have two OSGI blueprint bundles. One of them is like a service and another is using it. I'm running them on karaf. So, I want to implement functionality so when I'm stopping service then my other bundle also should be stopped. My xml's

    <?xml version="1.0" encoding="UTF-8"?>
<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:cm="http://aries.apache.org/blueprint/xmlns/blueprint-cm/v1.1.0"
    xsi:schemaLocation="http://www.osgi.org/xmlns/blueprint/v1.0.0 http://www.osgi.org/xmlns/blueprint/v1.0.0/blueprint.xsd ">

    <reference id="weatherService" availability="mandatory" interface="com.myslyv4uk.weather.api.WeatherService" />  

    <bean id="showWeatherImpl" class="com.myslyv4uk.client.impl.ShowWeatherServiceImpl"
        init-method="start" destroy-method="stop" >
        <argument ref="weatherService" />
    </bean>

</blueprint>

<?xml version="1.0" encoding="UTF-8"?>
<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.osgi.org/xmlns/blueprint/v1.0.0 http://www.osgi.org/xmlns/blueprint/v1.0.0/blueprint.xsd ">

    <bean id="weatherServiceImpl" class="com.myslyv4uk.weather.impl.WeatherServiceImpl"
        init-method="start" destroy-method="stop" />

    <service ref="weatherServiceImpl">
        <interfaces>
            <value>com.myslyv4uk.weather.api.WeatherService</value>
        </interfaces>
    </service>  
</blueprint>

Java code skipped. I will just say that ShowWeatherService uses WeatherService to print random number. They both have start/stop method. I need to implement configuration or functionality in such way so after uninstall WeatherService bundle from karaf also ShowWeatherService was stopped. The problem is that I cannot do reference from WeatherService to ShowWeatherService because it will be cyclic reference it this bundles won't start up. What should I do? How could I terminate bundle from other bundle?

Answer 1

WARNING

In this answer I explain how to stop a Blueprint bundle when a required service disappears. This code works as intended, however it is a bad idea for various reasons.

---

You can register a listener on bind/unbind of a service, and act upon the removal of the service. This is an example on how to do it.

<blueprint xmlns="http://www.osgi.org/xmlns/blueprint/v1.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:cm="http://aries.apache.org/blueprint/xmlns/blueprint-cm/v1.1.0"
    xsi:schemaLocation="http://www.osgi.org/xmlns/blueprint/v1.0.0 http://www.osgi.org/xmlns/blueprint/v1.0.0/blueprint.xsd ">

    <bean id="referenceListener" class="your.ReferenceListener">
        <property name="bundleContext" ref="blueprintBundleContext"/>
    </bean>

    <reference id="weatherService"
               availability="mandatory"
               interface="com.myslyv4uk.weather.api.WeatherService">
        <reference-listener ref="referenceListener"
                            unbind-method="unbind" />
    </reference>

    <bean id="showWeatherImpl" class="com.myslyv4uk.client.impl.ShowWeatherServiceImpl"
        init-method="start" destroy-method="stop" >
        <argument ref="weatherService" />
    </bean>

</blueprint>

The referenceListener bean is called when the service is removed. By injecting the bundle context, you can stop the bundle itself:

public class ReferenceListener {

private Logger log; // set this up
private BundleContext bundleContext;

public void setBundleContext(BundleContext bundleContext) {
    this.bundleContext = bundleContext;
}

// Called when the service is injected
public void bind(ServiceReference<?> sr) {
    log.info("Bind of ServiceReference {} to bundle {}",
            sr, bundleContext.getBundle());
}

// Called when the service is removed
public void unbind(ServiceReference<?> sr) {
    log.info("Unbind of ServiceReference {} from bundle {}",
            sr, bundleContext.getBundle());
    try {
        if (bundleContext.getBundle().getState() == Bundle.ACTIVE) {
            log.warn("Bundle {} will be stopped after unbind of mandatory ServiceReference {}",
                    bundleContext.getBundle(), sr);
            bundleContext.getBundle().stop();
        }

    } catch (BundleException e) {
        log.error("Cannot stop bundle {} after unbind of ServiceReference {}",
                bundleContext.getBundle().getBundleId(),
                sr,
                e);
    }
}
}

This solution works but has some drawbacks, for example if you restart the container the service is removed, thus setting the bundle in STOPPED state.