--- /dev/null 2013-02-14 00:07:37.184020992 -0500 +++ new/src/share/classes/java/util/stream/AbstractShortCircuitTask.java 2013-02-21 14:11:03.000000000 -0500 @@ -0,0 +1,172 @@ +/* + * Copyright (c) 2012, Oracle and/or its affiliates. All rights reserved. + * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. + * + * This code is free software; you can redistribute it and/or modify it + * under the terms of the GNU General Public License version 2 only, as + * published by the Free Software Foundation. Oracle designates this + * particular file as subject to the "Classpath" exception as provided + * by Oracle in the LICENSE file that accompanied this code. + * + * This code is distributed in the hope that it will be useful, but WITHOUT + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or + * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License + * version 2 for more details (a copy is included in the LICENSE file that + * accompanied this code). + * + * You should have received a copy of the GNU General Public License version + * 2 along with this work; if not, write to the Free Software Foundation, + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. + * + * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA + * or visit www.oracle.com if you need additional information or have any + * questions. + */ +package java.util.stream; + +import java.util.Spliterator; +import java.util.concurrent.atomic.AtomicReference; + +/** + * Abstract class for fork-join tasks used to implement short-circuiting + * stream ops, which can produce a result without processing all elements of the stream. + * + * @param Type of elements input to the pipeline + * @param Type of elements output from the pipeline + * @param Type of intermediate result, may be different from operation result type + * @param Type of child and sibling tasks + * @since 1.8 + */ +abstract class AbstractShortCircuitTask> + extends AbstractTask { + /** The result for this computation; this is shared among all tasks and set exactly once */ + protected final AtomicReference sharedResult; + + /** + * Indicates whether this task has been canceled. Tasks may cancel other tasks in the computation + * under various conditions, such as in a find-first operation, a task that finds a value will cancel + * all tasks that are later in the encounter order. + */ + protected volatile boolean canceled; + + /** Constructor for root nodes */ + protected AbstractShortCircuitTask(PipelineHelper helper) { + super(helper); + sharedResult = new AtomicReference<>(null); + } + + /** Constructor for non-root nodes */ + protected AbstractShortCircuitTask(T parent, Spliterator spliterator) { + super(parent, spliterator); + sharedResult = parent.sharedResult; + } + + /** + * Return the value indicating the computation completed with no task finding a short-circuitable result. + * For example, for a "find" operation, this might be null or an empty {@code Optional}. + */ + protected abstract R getEmptyResult(); + + @Override + protected boolean canCompute() { + // Have we already found an answer? + if (sharedResult.get() != null) { + tryComplete(); + return false; + } else if (taskCanceled()) { + setLocalResult(getEmptyResult()); + tryComplete(); + return false; + } + else { + return true; + } + } + + /** + * Declare that a globally valid result has been found. If another task has not already found the answer, + * the result is installed in {@code sharedResult}. The {@code compute()} method will check {@code sharedResult} + * before proceeding with computation, so this causes the computation to terminate early. + */ + protected void shortCircuit(R result) { + if (result != null) + sharedResult.compareAndSet(null, result); + } + + /** + * Set a local result for this task. If this task is the root, set the shared result instead (if not already set). + */ + @Override + protected void setLocalResult(R localResult) { + if (isRoot()) { + if (localResult != null) + sharedResult.compareAndSet(null, localResult); + } + else + super.setLocalResult(localResult); + } + + /** Retrieve the local result for this task */ + @Override + public R getRawResult() { + return getLocalResult(); + } + + /** Retrieve the local result for this task. If this task is the root, retrieves the shared result instead. */ + @Override + public R getLocalResult() { + if (isRoot()) { + R answer = sharedResult.get(); + return (answer == null) ? getEmptyResult() : answer; + } + else + return super.getLocalResult(); + } + + /** Set this node as canceled */ + protected void cancel() { + canceled = true; + } + + /** + * Query whether this task is canceled. A task is considered canceled if it or any of its parents + * have been canceled. + */ + protected boolean taskCanceled() { + boolean cancel = canceled; + if (!cancel) + for (T parent = getParent(); !cancel && parent != null; parent = parent.getParent()) + cancel = parent.canceled; + return cancel; + } + + /** + * Cancel all tasks which succeed this one in the encounter order. This includes canceling all the current + * task's later siblings, as well as the later siblings of all its parents. + */ + protected void cancelLaterNodes() { + T parent = getParent(); + for (T sibling = this.nextSibling; sibling != null; sibling = sibling.nextSibling) + if (!sibling.canceled) + sibling.canceled = true; + // Go up the tree, cancel later siblings of all parents + if (parent != null) + parent.cancelLaterNodes(); + } + + /** + * Returns whether this node is a "leftmost" node -- whether the path from the root to this node involves + * only traversing leftmost child links. For a leaf node, this means it is the first leaf node in the + * encounter order. + */ + protected boolean isLeftmostNode() { + T node = (T) this; + while (node != null) { + T parent = node.getParent(); + if (parent != null && parent.children != node) + return false; + node = parent; + } + return true; + } +}