brooklyn.management.internal.SubscriptionTracker Maven / Gradle / Ivy

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package brooklyn.management.internal;

import java.util.Collection;

import brooklyn.entity.Entity;
import brooklyn.entity.Group;
import brooklyn.event.Sensor;
import brooklyn.event.SensorEventListener;
import brooklyn.management.SubscriptionContext;
import brooklyn.management.SubscriptionHandle;

import com.google.common.collect.HashMultimap;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.SetMultimap;

/**
 * Tracks subscriptions associated that are registered with particular entities. Gives utilities for unsubscribing from all
 * subscriptions on a given entity, etc.
 */
public class SubscriptionTracker {

    // This class is thread-safe. All modifications to subscriptions are synchronized on the 
    // "subscriptions" field. However, calls to alien code (i.e. context.subscribe etc) is
    // done without holding the lock.
    //
    // If two threads do subscribe() and unsubscribeAll() concurrently, then it's non-derministic
    // whether the subscription will be in place at the end (but that's unavoidable). However, it
    // is guaranteed that the internal state of the SubscriptionTracker will be consistent: if
    // the "subscriptions" includes the new subscription then that subscription will really exist,
    // and vice versa.
    
    protected SubscriptionContext context;
    
    private final SetMultimap subscriptions = HashMultimap.create();

    public SubscriptionTracker(SubscriptionContext subscriptionContext) {
        this.context = subscriptionContext;
    }
    
    /** @see SubscriptionContext#subscribe(Entity, Sensor, SensorEventListener) */
    public  SubscriptionHandle subscribe(Entity producer, Sensor sensor, SensorEventListener listener) {
        SubscriptionHandle handle = context.subscribe(producer, sensor, listener);
        synchronized (subscriptions) {
            subscriptions.put(producer, handle);
        }
        return handle;
    }
    
    /** @see SubscriptionContext#subscribeToChildren(Entity, Sensor, SensorEventListener) */
    public  SubscriptionHandle subscribeToChildren(Entity parent, Sensor sensor, SensorEventListener listener) {
        SubscriptionHandle handle = context.subscribeToChildren(parent, sensor, listener);
        synchronized (subscriptions) {
            subscriptions.put(parent, handle);
        }
        return handle;
    }

    /**
     * @see SubscriptionContext#subscribeToMembers(Group, Sensor, SensorEventListener)
     */
    public  SubscriptionHandle subscribeToMembers(Group parent, Sensor sensor, SensorEventListener listener) {
        SubscriptionHandle handle = context.subscribeToMembers(parent, sensor, listener);
        synchronized (subscriptions) {
            subscriptions.put(parent, handle);
        }
        return handle;
    }    

    /**
     * Unsubscribes the given producer.
     *
     * @see SubscriptionContext#unsubscribe(SubscriptionHandle)
     */
    public boolean unsubscribe(Entity producer) {
        Collection handles;
        synchronized (subscriptions) {
            handles = subscriptions.removeAll(producer);
        }
        if (handles != null) {
            for (SubscriptionHandle handle : handles) {
                context.unsubscribe(handle);
            }
            return true;
        }
        return false;
    }

    /**
    * Unsubscribes the given producer.
    *
    * @see SubscriptionContext#unsubscribe(SubscriptionHandle)
    */
   public boolean unsubscribe(Entity producer, SubscriptionHandle handle) {
       synchronized (subscriptions) {
           subscriptions.remove(producer, handle);
       }
       return context.unsubscribe(handle);
   }

    /**
    * @return an ordered list of all subscription handles
    */
   public Collection getAllSubscriptions() {
       synchronized (subscriptions) {
           return ImmutableList.copyOf(subscriptions.values());
       }
   }
   
   public void unsubscribeAll() {
       Collection subscriptionsSnapshot;
       synchronized (subscriptions) {
           subscriptionsSnapshot = ImmutableList.copyOf(subscriptions.values());
           subscriptions.clear();
       }
       for (SubscriptionHandle s: subscriptionsSnapshot) {
           context.unsubscribe(s);
       }
   }
}