murblanc commented on a change in pull request #1962:
URL: https://github.com/apache/lucene-solr/pull/1962#discussion_r517211398
##########
File path:
solr/core/src/java/org/apache/solr/cluster/events/impl/ClusterEventProducerFactory.java
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@@ -0,0 +1,173 @@
+package org.apache.solr.cluster.events.impl;
+
+import org.apache.solr.api.ContainerPluginsRegistry;
+import org.apache.solr.cluster.events.ClusterEvent;
+import org.apache.solr.cluster.events.ClusterEventListener;
+import org.apache.solr.cluster.events.ClusterEventProducer;
+import org.apache.solr.cluster.events.ClusterEventProducerBase;
+import org.apache.solr.cluster.events.NoOpProducer;
+import org.apache.solr.core.CoreContainer;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.lang.invoke.MethodHandles;
+import java.util.Set;
+
+/**
+ * This class helps in handling the initial registration of plugin-based
listeners,
+ * when both the final {@link ClusterEventProducer} implementation and
listeners
+ * are configured using plugins.
+ */
+public class ClusterEventProducerFactory extends ClusterEventProducerBase {
+ private static final Logger log =
LoggerFactory.getLogger(MethodHandles.lookup().lookupClass());
+
+ private ContainerPluginsRegistry.PluginRegistryListener
initialPluginListener;
+ private boolean created = false;
+
+ public ClusterEventProducerFactory(CoreContainer cc) {
+ super(cc);
+ initialPluginListener = new
ContainerPluginsRegistry.PluginRegistryListener() {
+ @Override
+ public void added(ContainerPluginsRegistry.ApiInfo plugin) {
+ if (plugin == null || plugin.getInstance() == null) {
+ return;
+ }
+ Object instance = plugin.getInstance();
+ if (instance instanceof ClusterEventListener) {
+ registerListener((ClusterEventListener) instance);
+ }
+ }
+
+ @Override
+ public void deleted(ContainerPluginsRegistry.ApiInfo plugin) {
+ if (plugin == null || plugin.getInstance() == null) {
+ return;
+ }
+ Object instance = plugin.getInstance();
+ if (instance instanceof ClusterEventListener) {
+ unregisterListener((ClusterEventListener) instance);
+ }
+ }
+
+ @Override
+ public void modified(ContainerPluginsRegistry.ApiInfo old,
ContainerPluginsRegistry.ApiInfo replacement) {
+ added(replacement);
+ deleted(old);
+ }
+ };
+ }
+
+ @Override
+ public Set<ClusterEvent.EventType> getSupportedEventTypes() {
+ return NoOpProducer.ALL_EVENT_TYPES;
+ }
+
+ /**
+ * This method returns an initial plugin registry listener that helps to
capture the
+ * freshly loaded listener plugins before the final cluster event producer
is created.
+ * @return initial listener
+ */
+ public ContainerPluginsRegistry.PluginRegistryListener
getPluginRegistryListener() {
+ return initialPluginListener;
+ }
+
+ /**
+ * Create a {@link ClusterEventProducer} based on the current plugin
configurations.
+ * <p>NOTE: this method can only be called once because it has side-effects,
such as
+ * transferring the initially collected listeners to the resulting
producer's instance, and
+ * installing a {@link
org.apache.solr.api.ContainerPluginsRegistry.PluginRegistryListener}.
+ * Calling this method more than once will result in an exception.</p>
+ * @param plugins current plugin configurations
+ * @return configured instance of cluster event producer (with side-effects,
see above)
+ */
+ public DelegatingClusterEventProducer create(ContainerPluginsRegistry
plugins) {
+ if (created) {
+ throw new RuntimeException("this factory can be called only once!");
+ }
+ final DelegatingClusterEventProducer clusterEventProducer = new
DelegatingClusterEventProducer(cc);
+ // since this is a ClusterSingleton, register it as such
+
cc.getClusterSingletons().getSingletons().put(ClusterEventProducer.PLUGIN_NAME
+"_delegate", clusterEventProducer);
+ ContainerPluginsRegistry.ApiInfo clusterEventProducerInfo =
plugins.getPlugin(ClusterEventProducer.PLUGIN_NAME);
+ if (clusterEventProducerInfo != null) {
+ // the listener in ClusterSingletons already registered it
+ clusterEventProducer.setDelegate((ClusterEventProducer)
clusterEventProducerInfo.getInstance());
+ } else {
+ // use the default NoOp impl
+ }
+ // transfer those listeners that were already registered to the initial
impl
+ transferListeners(clusterEventProducer, plugins);
+ // install plugin registry listener
+ ContainerPluginsRegistry.PluginRegistryListener pluginListener = new
ContainerPluginsRegistry.PluginRegistryListener() {
+ @Override
+ public void added(ContainerPluginsRegistry.ApiInfo plugin) {
+ if (plugin == null || plugin.getInstance() == null) {
+ return;
+ }
+ Object instance = plugin.getInstance();
+ if (instance instanceof ClusterEventListener) {
+ ClusterEventListener listener = (ClusterEventListener) instance;
+ clusterEventProducer.registerListener(listener);
+ } else if (instance instanceof ClusterEventProducer) {
+ // replace the existing impl
+ if (cc.getClusterEventProducer() instanceof
DelegatingClusterEventProducer) {
+ ((DelegatingClusterEventProducer) cc.getClusterEventProducer())
+ .setDelegate((ClusterEventProducer) instance);
+ } else {
+ log.warn("Can't configure plugin-based ClusterEventProducer while
CoreContainer is still loading - " +
+ " using existing implementation {}",
cc.getClusterEventProducer().getClass().getName());
+ }
+ }
+ }
+
+ @Override
+ public void deleted(ContainerPluginsRegistry.ApiInfo plugin) {
+ if (plugin == null || plugin.getInstance() == null) {
+ return;
+ }
+ Object instance = plugin.getInstance();
+ if (instance instanceof ClusterEventListener) {
+ ClusterEventListener listener = (ClusterEventListener) instance;
+ clusterEventProducer.unregisterListener(listener);
+ } else if (instance instanceof ClusterEventProducer) {
+ // replace the existing impl with NoOp
+ if (cc.getClusterEventProducer() instanceof
DelegatingClusterEventProducer) {
+ ((DelegatingClusterEventProducer) cc.getClusterEventProducer())
+ .setDelegate(new NoOpProducer(cc));
+ } else {
+ log.warn("Can't configure plugin-based ClusterEventProducer while
CoreContainer is still loading - " +
+ " using existing implementation {}",
cc.getClusterEventProducer().getClass().getName());
+ }
+ }
+ }
+
+ @Override
+ public void modified(ContainerPluginsRegistry.ApiInfo old,
ContainerPluginsRegistry.ApiInfo replacement) {
+ added(replacement);
+ deleted(old);
+ }
+ };
+ plugins.registerListener(pluginListener);
+ created = true;
+ return clusterEventProducer;
+ }
+
+ private void transferListeners(ClusterEventProducer target,
ContainerPluginsRegistry plugins) {
Review comment:
Would there be a way to register listeners into an intermediate object
(not tied to any specific producer), then have event producers feed events into
this object (conceptually it would behave like a queue, but the implementation
can be direct listener method calls). This would save having methods such as
this one (and would not require having a producer in order to register
listeners, if that helps...).
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