path: root/plugin/icedteanp/java/sun/applet/PluginMessageConsumer.java

/* 
   Copyright (C) 2008  Red Hat

This file is part of IcedTea.

IcedTea is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

IcedTea 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 for more details.

You should have received a copy of the GNU General Public License
along with IcedTea; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
conditions of the GNU General Public License cover the whole
combination.

As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
modules, and to copy and distribute the resulting executable under
terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
module.  An independent module is a module which is not derived from
or based on this library.  If you modify this library, you may extend
this exception to your version of the library, but you are not
obligated to do so.  If you do not wish to do so, delete this
exception statement from your version. */

package sun.applet;

import java.util.ArrayList;
import java.util.LinkedList;

class PluginMessageConsumer {

    private static final int MAX_PARALLEL_INITS = 1;

    // Each initialization requires 5 responses (tag, handle, width, proxy, cookie) 
    // before the message stack unlocks/collapses. This works out well because we 
    // want to allow upto 5 parallel tasks anyway
    private static final int MAX_WORKERS = MAX_PARALLEL_INITS * 4;
    private static final int PRIORITY_WORKERS = MAX_PARALLEL_INITS * 2;

    private static LinkedList<String> priorityWaitQueue = new LinkedList<String>();

    private LinkedList<String> readQueue = new LinkedList<String>();
    private ArrayList<PluginMessageHandlerWorker> workers = new ArrayList<PluginMessageHandlerWorker>();
    private PluginStreamHandler streamHandler;
    private ConsumerThread consumerThread = new ConsumerThread();

    public PluginMessageConsumer(PluginStreamHandler streamHandler) {
        this.streamHandler = streamHandler;
        this.consumerThread.start();
    }

    /** 
     * Registers a reference to wait for. Responses to registered priority 
     * references get handled by priority worker if normal workers are busy.
     *
     * @param reference The reference to give priority to
     */
    public static void registerPriorityWait(Long reference) {
        PluginDebug.debug("Registering priority for reference ", reference);
        registerPriorityWait("reference " + reference.toString());
    }

    /** 
     * Registers a string to wait for.
     *
     * @param searchString the string to look for in a response
     */
    private static void registerPriorityWait(String searchString) {
        PluginDebug.debug("Registering priority for string ", searchString);
        synchronized (priorityWaitQueue) {
            if (!priorityWaitQueue.contains(searchString)) {
                priorityWaitQueue.add(searchString);
            }
        }
    }

    /** 
     * Unregisters a priority string to wait for.
     *
     * @param searchString The string to unregister from the priority list
     */
    private static void unRegisterPriorityWait(String searchString) {
        synchronized (priorityWaitQueue) {
            priorityWaitQueue.remove(searchString);
        }
    }

    private static String getPriorityStrIfPriority(String message) {

        // Destroy messages are permanently high priority
        if (message.endsWith("destroy")) {
            return "destroy";
        }

        synchronized (priorityWaitQueue) {
            for (String priorityStr : priorityWaitQueue) {
                if (message.indexOf(priorityStr) > 0) {
                    return priorityStr; 
                }
            }
        }

        return null;
    }

    public void queue(String message) {
        synchronized (readQueue) {
            readQueue.addLast(message);
        }

        // Wake that lazy consumer thread
        consumerThread.notifyHasWork();
    }

    protected class ConsumerThread extends Thread {

        public ConsumerThread() {
            super("PluginMessageConsumer.ConsumerThread");
        }

        // Notify that either work is ready to do, or a worker is available
        public synchronized void notifyHasWork() {
            notifyAll();
        }

        // Wait a bit until either work is ready to do, or a worker is available
        public synchronized void waitForWork() {
            try {
                // Do not wait indefinitely to avoid the potential of deadlock
                wait(1000);
            } catch (InterruptedException e) {
                // Should not typically occur
                e.printStackTrace();
            }
        }

        /**
         * Scans the readQueue for priority messages and brings them to the front
         */
        private void bringPriorityMessagesToFront() {
            synchronized (readQueue) {

                // iterate through the list
                for (int i = 0; i < readQueue.size(); i++) {

                    // remove element at i to inspect it
                    String message = readQueue.remove(i);

                    // if element at i is a priority msg, bring it forward
                    if (getPriorityStrIfPriority(message) != null) {
                        readQueue.addFirst(message);
                    } else { // else keep it where it was
                        readQueue.add(i, message);
                    }

                    // by the end the queue size is the same, so the 
                    // position indicator (i) is still valid
                }
            }
        }

        public void run() {

            while (true) {

                String message = null;

                synchronized (readQueue) {
                    message = readQueue.poll();
                }

                if (message != null) {

                    String priorityStr = getPriorityStrIfPriority(message);
                    boolean isPriorityResponse = (priorityStr != null);

                    //PluginDebug.debug("Message " + message + " (priority=" + isPriorityResponse + ") ready to be processed. Looking for free worker...");
                    final PluginMessageHandlerWorker worker = getFreeWorker(isPriorityResponse);

                    if (worker == null) {
                        synchronized (readQueue) {
                            readQueue.addFirst(message);
                        }

                        // re-scan to see if any priority message came in
                        bringPriorityMessagesToFront();

                        continue; // re-loop to try next msg
                    }

                    if (isPriorityResponse) {
                        unRegisterPriorityWait(priorityStr);
                    }

                    worker.setmessage(message);
                    worker.notifyHasWork();

                } else {
                    waitForWork();
                }
            }
        }
    }

    private PluginMessageHandlerWorker getFreeWorker(boolean prioritized) {

        for (PluginMessageHandlerWorker worker : workers) {
            if (worker.isFree(prioritized)) {
                PluginDebug.debug("Found free worker (", worker.isPriority(), ") with id ", worker.getWorkerId());
                // mark it busy before returning
                worker.busy();
                return worker;
            }
        }

        // If we have less than MAX_WORKERS, create a new worker
        if (workers.size() <= MAX_WORKERS) {
            PluginMessageHandlerWorker worker = null;

            if (workers.size() < (MAX_WORKERS - PRIORITY_WORKERS)) {
                PluginDebug.debug("Cannot find free worker, creating worker ", workers.size());
                worker = new PluginMessageHandlerWorker(this, streamHandler, workers.size(), false);
            } else if (prioritized) {
                PluginDebug.debug("Cannot find free worker, creating priority worker ", workers.size());
                worker = new PluginMessageHandlerWorker(this, streamHandler, workers.size(), true);
            } else {
                return null;
            }

            worker.start();
            worker.busy();
            workers.add(worker);
            return worker;

        }

        // No workers available. Better luck next time! 
        return null;
    }
}