FELIX-6778 Reduce number of re-creation(s) of SCR Component Registry thread

scr/src/main/java/org/apache/felix/scr/impl/Activator.java

@@ -97,7 +97,7 @@ public class Activator extends AbstractExtender
     private ComponentRegistry m_componentRegistry;
 
     //  thread acting upon configurations
-    private ComponentActorThread m_componentActor;
+    private ComponentActorExecutor m_componentActor;
 
     private ServiceRegistration<ServiceComponentRuntime> m_runtime_reg;
 
@@ -210,7 +210,8 @@ protected void doStart() throws Exception
 
         // prepare component registry
         m_componentBundles = new HashMap<>();
-        m_componentRegistry = new ComponentRegistry( this.m_configuration, this.logger );
+        m_componentActor = new ComponentActorExecutor( this.logger );
+        m_componentRegistry = new ComponentRegistry( this.m_configuration, this.logger, this.m_componentActor );
 
         final ServiceComponentRuntimeImpl runtime = new ServiceComponentRuntimeImpl( m_globalContext, m_componentRegistry );
         m_runtime_reg = m_context.registerService( ServiceComponentRuntime.class,
@@ -222,12 +223,6 @@ protected void doStart() throws Exception
         logger.log(Level.INFO, " Version = {0}",
             null, m_bundle.getVersion().toString() );
 
-        // create and start the component actor
-        m_componentActor = new ComponentActorThread( this.logger );
-        Thread t = new Thread( m_componentActor, "SCR Component Actor" );
-        t.setDaemon( true );
-        t.start();
-
         super.doStart();
 
         m_componentCommands = new ComponentCommands(m_context, runtime, m_configuration);
@@ -427,14 +422,13 @@ public void doStop() throws Exception
         // dispose component registry
         if ( m_componentRegistry != null )
         {
-            m_componentRegistry.shutdown();
             m_componentRegistry = null;
         }
 
         // terminate the actor thread
         if ( m_componentActor != null )
         {
-            m_componentActor.terminate();
+            m_componentActor.shutdownNow();
             m_componentActor = null;
         }
         ClassUtils.setFrameworkWiring(null);

scr/src/main/java/org/apache/felix/scr/impl/BundleComponentActivator.java

@@ -30,6 +30,7 @@
 import java.util.Map;
 import java.util.StringTokenizer;
 import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ScheduledExecutorService;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicBoolean;
 
@@ -81,7 +82,7 @@ public class BundleComponentActivator implements ComponentActivator
     private final List<ComponentHolder<?>> m_holders = new ArrayList<>();
 
     // thread acting upon configurations
-    private final ComponentActorThread m_componentActor;
+    private final ScheduledExecutorService m_componentActor;
 
     // true as long as the dispose method is not called
     private final AtomicBoolean m_active = new AtomicBoolean( true );
@@ -196,7 +197,7 @@ public void removeServiceListener(String serviceFilterString,
      */
     public BundleComponentActivator(final ScrLogger scrLogger,
             final ComponentRegistry componentRegistry,
-            final ComponentActorThread componentActor,
+            final ScheduledExecutorService componentActor,
             final BundleContext context,
             final ScrConfiguration configuration,
             final List<ComponentMetadata> cachedComponentMetadata,
@@ -712,10 +713,10 @@ public void schedule(Runnable task)
     {
         if ( isActive() )
         {
-            ComponentActorThread cat = m_componentActor;
+            ScheduledExecutorService cat = m_componentActor;
             if ( cat != null )
             {
-                cat.schedule( task );
+                cat.submit( task );
             }
             else
             {
@@ -762,7 +763,7 @@ public <T> void leaveCreate(ServiceReference<T> serviceReference)
     @Override
     public <T> void missingServicePresent(ServiceReference<T> serviceReference)
     {
-        m_componentRegistry.missingServicePresent( serviceReference, m_componentActor );
+        m_componentRegistry.missingServicePresent( serviceReference );
     }
 
     @Override

scr/src/main/java/org/apache/felix/scr/impl/ComponentActorExecutor.java

@@ -0,0 +1,70 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.felix.scr.impl;
+
+
+import java.util.concurrent.ScheduledThreadPoolExecutor;
+import java.util.concurrent.ThreadFactory;
+
+import org.apache.felix.scr.impl.logger.InternalLogger.Level;
+import org.apache.felix.scr.impl.logger.ScrLogger;
+
+
+/**
+ * The <code>ComponentActorExecutor</code> is the thread used to act upon registered
+ * components of the service component runtime.
+ * This is also used by the ComponentRegistry to schedule service.changecount updates.
+ */
+class ComponentActorExecutor extends ScheduledThreadPoolExecutor
+{
+
+    private static final ThreadFactory THREAD_FACTORY = new ThreadFactory()
+    {
+        @Override
+        public Thread newThread(Runnable r)
+        {
+            Thread thread = new Thread(r, "SCR Component Actor");
+            thread.setDaemon(true);
+            return thread;
+        }
+    };
+
+    private final ScrLogger logger;
+
+    ComponentActorExecutor(final ScrLogger log )
+    {
+        super( 1, THREAD_FACTORY );
+        logger = log;
+    }
+
+    @Override
+    protected void beforeExecute(Thread t, Runnable r)
+    {
+        logger.log(Level.DEBUG, "Running task: " + r, null);
+    }
+
+    @Override
+    protected void afterExecute(Runnable r, Throwable t)
+    {
+        if (t != null)
+        {
+            logger.log(Level.ERROR, "Unexpected problem executing task " + r, t);
+        }
+    }
+}