/*
 * The Apache Software License, Version 1.1
 *
 * Copyright (c) 2001-2002 The Apache Software Foundation.  All rights
 * reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in
 *    the documentation and/or other materials provided with the
 *    distribution.
 *
 * 3. The end-user documentation included with the redistribution, if
 *    any, must include the following acknowlegement:
 *       "This product includes software developed by the
 *        Apache Software Foundation (http://www.apache.org/)."
 *    Alternately, this acknowlegement may appear in the software itself,
 *    if and wherever such third-party acknowlegements normally appear.
 *
 * 4. The names "The Jakarta Project", "Ant", and "Apache Software
 *    Foundation" must not be used to endorse or promote products derived
 *    from this software without prior written permission. For written
 *    permission, please contact apache@apache.org.
 *
 * 5. Products derived from this software may not be called "Apache"
 *    nor may "Apache" appear in their names without prior written
 *    permission of the Apache Group.
 *
 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED.  IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 * ====================================================================
 *
 * This software consists of voluntary contributions made by many
 * individuals on behalf of the Apache Software Foundation.  For more
 * information on the Apache Software Foundation, please see
 * <http://www.apache.org/>.
 */
package org.apache.tools.ant.taskdefs;

import org.apache.tools.ant.Task;
import org.apache.tools.ant.TaskContainer;
import org.apache.tools.ant.BuildException;
import org.apache.tools.ant.Location;
import org.apache.tools.ant.util.StringUtils;

import java.util.Vector;
import java.util.Enumeration;
import java.io.PrintStream;
import java.io.ByteArrayOutputStream;



/**
 * Implements a multi threaded task execution.
 * <p>
 * @author Thomas Christen <a href="mailto:chr@active.ch">chr@active.ch</a>
 * @author Conor MacNeill
 * @since Ant 1.4
 *
 * @ant.task category="control"
 */
public class Parallel extends Task
                      implements TaskContainer {

    /** Collection holding the nested tasks */
    private Vector nestedTasks = new Vector();


    /**
     * Add a nested task to execute parallel (asynchron).
     * <p>
     * @param nestedTask  Nested task to be executed in parallel
     */
    public void addTask(Task nestedTask) throws BuildException {
        nestedTasks.addElement(nestedTask);
    }

    /**
     * Block execution until the specified time or for a
     * specified amount of milliseconds and if defined,
     * execute the wait status.
     */
    public void execute() throws BuildException {
        final TaskThread[] threads = new TaskThread[nestedTasks.size()];
        int threadNumber = 0;
        final CountDown barrier = new CountDown(threads.length);  // Our signal that an exception occured
        for (Enumeration e = nestedTasks.elements(); e.hasMoreElements();
             threadNumber++) {
            Task nestedTask = (Task) e.nextElement();
            threads[threadNumber] = new TaskThread(threadNumber, nestedTask, barrier);
        }

        // now start all threads
        for (int i = 0; i < threads.length; ++i) {
            threads[i].start();
        }

        try {
            barrier.acquire();
        } catch (InterruptedException e) {
        }

        // Interrupt all threads
        for (int i = 0; i < threads.length; ++i) {
            threads[i].interrupt();
        }

        // now did any of the threads throw an exception
        StringBuffer exceptionMessage = new StringBuffer();
        int numExceptions = 0;
        Throwable firstException = null;
        Location firstLocation = Location.UNKNOWN_LOCATION;;
        for (int i = 0; i < threads.length; ++i) {
            Throwable t = threads[i].getException();
            if (t != null) {
                numExceptions++;
                if (firstException == null) {
                    firstException = t;
                }
                if (t instanceof BuildException &&
                        firstLocation == Location.UNKNOWN_LOCATION) {
                    firstLocation = ((BuildException) t).getLocation();
                }
                exceptionMessage.append(StringUtils.LINE_SEP);
                // I much prefer a exception stack trace to a useless
                // exception message, personally :)
                ByteArrayOutputStream baos = new ByteArrayOutputStream();
                PrintStream ps = new PrintStream(baos);
                t.printStackTrace(ps);
                ps.flush();
                exceptionMessage.append(new String(baos.toByteArray()));
            }
        }

        if (numExceptions == 1) {
            if (firstException instanceof BuildException) {
                throw (BuildException) firstException;
            } else {
                throw new BuildException(firstException);
            }
        } else if (numExceptions > 1) {
            throw new BuildException(exceptionMessage.toString(),
                                     firstLocation);
        }
    }

    static class TaskThread extends Thread {
        private Throwable exception;
        private Task task;
        private int taskNumber;
        private CountDown barrier;

        /**
         * Construct a new TaskThread.<p>
         *
         * @param task the Task to be executed in a seperate thread
         */
        TaskThread(int taskNumber, Task task, CountDown barrier) {
            this.task = task;
            this.taskNumber = taskNumber;
            this.barrier = barrier;
        }

        /**
         * Executes the task within a thread and takes care about
         * Exceptions raised within the task.
         */
        public void run() {
            try {
                task.perform();
                barrier.release();
            } catch (Throwable t) {
                exception = t;
                barrier.breakOut();
            }
        }

        public Throwable getException() {
            return exception;
        }
    }

    static class CountDown {
        protected final int initialCount;
        protected int count;
        protected boolean breakout = false;

        /** Create a new CountDown with given count value **/
        public CountDown(int count) {
            this.count = initialCount = count;
        }

        /*
          This could use double-check, but doesn't out of concern
          for surprising effects on user programs stemming
          from lack of memory barriers with lack of synch.
        */
        public void acquire() throws InterruptedException {
            if (Thread.interrupted()) throw new InterruptedException();
            synchronized (this) {
                while (!breakout && (count > 0)) {
                    wait();
                }
            }
        }

        /**
         * Decrement the count.
         * After the initialCount'th release, all current and future
         * acquires will pass
         **/
        public synchronized void release() {
            if (--count == 0)
                notifyAll();
        }

        /**
         * Break out any threads waiting to acquire
         * the receiver
         */
        public synchronized void breakOut(){
            breakout = true;
            notifyAll();
        }
    }

}