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+/*
+ * 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 nginx.unit.websocket;
+
+import java.util.HashSet;
+import java.util.Set;
+
+import org.apache.juli.logging.Log;
+import org.apache.juli.logging.LogFactory;
+import org.apache.tomcat.util.ExceptionUtils;
+import org.apache.tomcat.util.res.StringManager;
+
+/**
+ * Provides a background processing mechanism that triggers roughly once a
+ * second. The class maintains a thread that only runs when there is at least
+ * one instance of {@link BackgroundProcess} registered.
+ */
+public class BackgroundProcessManager {
+
+ private final Log log =
+ LogFactory.getLog(BackgroundProcessManager.class);
+ private static final StringManager sm =
+ StringManager.getManager(BackgroundProcessManager.class);
+ private static final BackgroundProcessManager instance;
+
+
+ static {
+ instance = new BackgroundProcessManager();
+ }
+
+
+ public static BackgroundProcessManager getInstance() {
+ return instance;
+ }
+
+ private final Set<BackgroundProcess> processes = new HashSet<>();
+ private final Object processesLock = new Object();
+ private WsBackgroundThread wsBackgroundThread = null;
+
+ private BackgroundProcessManager() {
+ // Hide default constructor
+ }
+
+
+ public void register(BackgroundProcess process) {
+ synchronized (processesLock) {
+ if (processes.size() == 0) {
+ wsBackgroundThread = new WsBackgroundThread(this);
+ wsBackgroundThread.setContextClassLoader(
+ this.getClass().getClassLoader());
+ wsBackgroundThread.setDaemon(true);
+ wsBackgroundThread.start();
+ }
+ processes.add(process);
+ }
+ }
+
+
+ public void unregister(BackgroundProcess process) {
+ synchronized (processesLock) {
+ processes.remove(process);
+ if (wsBackgroundThread != null && processes.size() == 0) {
+ wsBackgroundThread.halt();
+ wsBackgroundThread = null;
+ }
+ }
+ }
+
+
+ private void process() {
+ Set<BackgroundProcess> currentProcesses = new HashSet<>();
+ synchronized (processesLock) {
+ currentProcesses.addAll(processes);
+ }
+ for (BackgroundProcess process : currentProcesses) {
+ try {
+ process.backgroundProcess();
+ } catch (Throwable t) {
+ ExceptionUtils.handleThrowable(t);
+ log.error(sm.getString(
+ "backgroundProcessManager.processFailed"), t);
+ }
+ }
+ }
+
+
+ /*
+ * For unit testing.
+ */
+ int getProcessCount() {
+ synchronized (processesLock) {
+ return processes.size();
+ }
+ }
+
+
+ void shutdown() {
+ synchronized (processesLock) {
+ processes.clear();
+ if (wsBackgroundThread != null) {
+ wsBackgroundThread.halt();
+ wsBackgroundThread = null;
+ }
+ }
+ }
+
+
+ private static class WsBackgroundThread extends Thread {
+
+ private final BackgroundProcessManager manager;
+ private volatile boolean running = true;
+
+ public WsBackgroundThread(BackgroundProcessManager manager) {
+ setName("WebSocket background processing");
+ this.manager = manager;
+ }
+
+ @Override
+ public void run() {
+ while (running) {
+ try {
+ Thread.sleep(1000);
+ } catch (InterruptedException e) {
+ // Ignore
+ }
+ manager.process();
+ }
+ }
+
+ public void halt() {
+ setName("WebSocket background processing - stopping");
+ running = false;
+ }
+ }
+}