Java tutorial
/* * 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 brooklyn.util.mutex; import java.util.List; import java.util.Set; import brooklyn.management.ManagementContext; import brooklyn.management.Task; import brooklyn.util.collections.MutableList; import brooklyn.util.collections.MutableSet; import brooklyn.util.task.Tasks; import brooklyn.util.time.Time; import com.google.common.base.Preconditions; import com.google.common.collect.ImmutableList; import com.google.common.collect.ImmutableSet; import com.google.common.collect.Iterables; /** A subclass of {@link SemaphoreWithOwners} * which additionally sets Task blocking information. * <p> * TODO As tasks are distributed this should support distribution across the management context. */ public class SemaphoreForTasks extends SemaphoreWithOwners { private static final long serialVersionUID = 7898283056223005952L; /** unused at present, but wanted on the API for when this may be federated */ @SuppressWarnings("unused") private final ManagementContext mgmt; final private MutableList<Task<?>> owningTasks = new MutableList<Task<?>>(); final private MutableSet<Task<?>> requestingTasks = new MutableSet<Task<?>>(); public SemaphoreForTasks(String name, ManagementContext mgmt) { super(name); this.mgmt = Preconditions.checkNotNull(mgmt); } public SemaphoreForTasks(String name, int permits, boolean fair, ManagementContext mgmt) { super(name, permits, fair); this.mgmt = Preconditions.checkNotNull(mgmt); } public synchronized Set<Task<?>> getRequestingTasks() { return ImmutableSet.copyOf(requestingTasks); } public synchronized List<Task<?>> getOwningTasks() { return ImmutableList.copyOf(owningTasks); } @Override protected synchronized void onRequesting() { if (!owningTasks.isEmpty() || !requestingTasks.isEmpty()) { Tasks.setBlockingTask(!requestingTasks.isEmpty() ? Iterables.getLast(requestingTasks) : Iterables.getFirst(owningTasks, null)); Tasks.setBlockingDetails( "Waiting on semaphore " + getName() + " (" + getDescription() + "); " + "queued at " + Time.makeDateString() + " when " + getRequestingThreads().size() + " ahead in queue"); } requestingTasks.addIfNotNull(Tasks.current()); super.onRequesting(); } @Override protected synchronized void onRequestFinished() { super.onRequestFinished(); requestingTasks.removeIfNotNull(Tasks.current()); Tasks.resetBlockingDetails(); Tasks.resetBlockingTask(); } @Override protected synchronized void onAcquired(int permits) { super.onAcquired(permits); for (int i = 0; i < permits; i++) owningTasks.appendIfNotNull(Tasks.current()); } @Override protected synchronized void onReleased(int permits) { super.onReleased(permits); for (int i = 0; i < permits; i++) owningTasks.removeIfNotNull(Tasks.current()); } @Override public synchronized String toString() { return super.toString() + "[" + "owningTasks=" + owningTasks + "; requestingTasks=" + requestingTasks + "]"; } }