| /* |
| * 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.openide.util.lookup.implspi; |
| |
| import java.lang.ref.Reference; |
| import java.lang.ref.ReferenceQueue; |
| import java.util.logging.Level; |
| import java.util.logging.Logger; |
| |
| /** |
| * Implementation of the active reference queue. |
| * @since 8.1 |
| */ |
| public final class ActiveQueue { |
| private ActiveQueue() {} |
| |
| private static final Logger LOGGER = Logger.getLogger(ActiveQueue.class.getName()); |
| private static Impl activeReferenceQueue; |
| |
| /** |
| * Gets the active reference queue. |
| * @return the singleton queue |
| */ |
| public static synchronized ReferenceQueue<Object> queue() { |
| if (activeReferenceQueue == null) { |
| activeReferenceQueue = new Impl(); |
| Daemon.ping(); |
| } |
| return activeReferenceQueue; |
| } |
| |
| private static final class Impl extends ReferenceQueue<Object> { |
| |
| Impl() { |
| } |
| |
| @Override |
| public Reference<Object> poll() { |
| throw new UnsupportedOperationException(); |
| } |
| |
| @Override |
| public Reference<Object> remove(long timeout) throws IllegalArgumentException, InterruptedException { |
| throw new InterruptedException(); |
| } |
| |
| @Override |
| public Reference<Object> remove() throws InterruptedException { |
| throw new InterruptedException(); |
| } |
| |
| final Reference<? extends Object> removeSuper() throws InterruptedException { |
| return super.remove(0); |
| } |
| } |
| |
| private static final class Daemon extends Thread { |
| private static boolean initialized; |
| private static Daemon running; |
| |
| public Daemon() { |
| super("Active Reference Queue Daemon"); |
| } |
| |
| static synchronized void ping() { |
| if (!initialized) { |
| try { |
| Daemon t = new Daemon(); |
| t.setPriority(Thread.MIN_PRIORITY); |
| t.setDaemon(true); |
| t.start(); |
| LOGGER.fine("starting thread"); |
| running = t; |
| } catch (SecurityException ex) { |
| LOGGER.log(Level.FINE, "cannot start thread", ex); |
| } finally { |
| initialized = true; |
| } |
| } |
| } |
| |
| static synchronized boolean isActive() { |
| return running != null; |
| } |
| |
| static synchronized Impl obtainQueue() { |
| return activeReferenceQueue; |
| } |
| |
| @Override |
| public void run() { |
| while (true) { |
| try { |
| Impl impl = obtainQueue(); |
| if (impl == null) { |
| return; |
| } |
| Reference<?> ref = impl.removeSuper(); |
| LOGGER.log(Level.FINE, "Got dequeued reference {0}", new Object[] { ref }); |
| if (!(ref instanceof Runnable)) { |
| LOGGER.log(Level.WARNING, "A reference not implementing runnable has been added to the Utilities.activeReferenceQueue(): {0}", ref.getClass()); |
| continue; |
| } |
| // do the cleanup |
| try { |
| ((Runnable) ref).run(); |
| } catch (ThreadDeath td) { |
| throw td; |
| } catch (Throwable t) { |
| // Should not happen. |
| // If it happens, it is a bug in client code, notify! |
| LOGGER.log(Level.WARNING, "Cannot process " + ref, t); |
| } finally { |
| // to allow GC |
| ref = null; |
| } |
| } catch (InterruptedException ex) { |
| // Can happen during VM shutdown, it seems. Ignore. |
| continue; |
| } |
| } |
| } |
| } |
| } |