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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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 * particular file as subject to the "Classpath" exception as provided

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 * 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).

 *

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package sun.nio.ch;

import java.io.IOException;

import java.nio.channels.ClosedSelectorException;

import java.nio.channels.Pipe;

import java.nio.channels.SelectionKey;

import java.nio.channels.Selector;

import java.nio.channels.spi.SelectorProvider;

import java.util.ArrayDeque;

import java.util.ArrayList;

import java.util.Deque;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

import java.util.function.Consumer;

/**

 * A multi-threaded implementation of Selector for Windows.

 *

 * @author Konstantin Kladko

 * @author Mark Reinhold

 */

class WindowsSelectorImpl extends SelectorImpl {

    // Initial capacity of the poll array

    private final int INIT_CAP = 8;

    // Maximum number of sockets for select().

    // Should be INIT_CAP times a power of 2

    private static final int MAX_SELECTABLE_FDS = 1024;

    // The list of SelectableChannels serviced by this Selector. Every mod

    // MAX_SELECTABLE_FDS entry is bogus, to align this array with the poll

    // array,  where the corresponding entry is occupied by the wakeupSocket

    private SelectionKeyImpl[] channelArray = new SelectionKeyImpl[INIT_CAP];

    // The global native poll array holds file decriptors and event masks

    private PollArrayWrapper pollWrapper;

    // The number of valid entries in  poll array, including entries occupied

    // by wakeup socket handle.

    private int totalChannels = 1;

    // Number of helper threads needed for select. We need one thread per

    // each additional set of MAX_SELECTABLE_FDS - 1 channels.

    private int threadsCount = 0;

    // A list of helper threads for select.

    private final List<SelectThread> threads = new ArrayList<SelectThread>();

    //Pipe used as a wakeup object.

    private final Pipe wakeupPipe;

    // File descriptors corresponding to source and sink

    private final int wakeupSourceFd, wakeupSinkFd;

    // Maps file descriptors to their indices in  pollArray

    private static final class FdMap extends HashMap<Integer, MapEntry> {

        static final long serialVersionUID = 0L;

        private MapEntry get(int desc) {

            return get(Integer.valueOf(desc));

        }

        private MapEntry put(SelectionKeyImpl ski) {

            return put(Integer.valueOf(ski.getFDVal()), new MapEntry(ski));

        }

        private MapEntry remove(SelectionKeyImpl ski) {

            Integer fd = Integer.valueOf(ski.getFDVal());

            MapEntry x = get(fd);

            if ((x != null) && (x.ski.channel() == ski.channel()))

                return remove(fd);

            return null;

        }

    }

    // class for fdMap entries

    private static final class MapEntry {

        final SelectionKeyImpl ski;

        long updateCount = 0;

        MapEntry(SelectionKeyImpl ski) {

            this.ski = ski;

        }

    }

    private final FdMap fdMap = new FdMap();

    // SubSelector for the main thread

    private final SubSelector subSelector = new SubSelector();

    private long timeout; //timeout for poll

    // Lock for interrupt triggering and clearing

    private final Object interruptLock = new Object();

    private volatile boolean interruptTriggered;

    // pending new registrations/updates, queued by implRegister and setEventOps

    private final Object updateLock = new Object();

    private final Deque<SelectionKeyImpl> newKeys = new ArrayDeque<>();

    private final Deque<SelectionKeyImpl> updateKeys = new ArrayDeque<>();

    WindowsSelectorImpl(SelectorProvider sp) throws IOException {

        super(sp);

        pollWrapper = new PollArrayWrapper(INIT_CAP);

        wakeupPipe = Pipe.open();

        wakeupSourceFd = ((SelChImpl)wakeupPipe.source()).getFDVal();

        // Disable the Nagle algorithm so that the wakeup is more immediate

        SinkChannelImpl sink = (SinkChannelImpl)wakeupPipe.sink();

        (sink.sc).socket().setTcpNoDelay(true);

        wakeupSinkFd = ((SelChImpl)sink).getFDVal();

        pollWrapper.addWakeupSocket(wakeupSourceFd, 0);

    }

    private void ensureOpen() {

        if (!isOpen())

            throw new ClosedSelectorException();

    }

    @Override

    protected int doSelect(Consumer<SelectionKey> action, long timeout)

        throws IOException

    {

        assert Thread.holdsLock(this);

        this.timeout = timeout; // set selector timeout

        processUpdateQueue();

        processDeregisterQueue();

        if (interruptTriggered) {

            resetWakeupSocket();

            return 0;

        }

        // Calculate number of helper threads needed for poll. If necessary

        // threads are created here and start waiting on startLock

        adjustThreadsCount();

        finishLock.reset(); // reset finishLock

        // Wakeup helper threads, waiting on startLock, so they start polling.

        // Redundant threads will exit here after wakeup.

        startLock.startThreads();

        // do polling in the main thread. Main thread is responsible for

        // first MAX_SELECTABLE_FDS entries in pollArray.

        try {

            begin();

            try {

                subSelector.poll();

            } catch (IOException e) {

                finishLock.setException(e); // Save this exception

            }

            // Main thread is out of poll(). Wakeup others and wait for them

            if (threads.size() > 0)

                finishLock.waitForHelperThreads();

          } finally {

              end();

          }

        // Done with poll(). Set wakeupSocket to nonsignaled  for the next run.

        finishLock.checkForException();

        processDeregisterQueue();

        int updated = updateSelectedKeys(action);

        // Done with poll(). Set wakeupSocket to nonsignaled  for the next run.

        resetWakeupSocket();

        return updated;

    }

    /**

     * Process new registrations and changes to the interest ops.

     */

    private void processUpdateQueue() {

        assert Thread.holdsLock(this);

        synchronized (updateLock) {

            SelectionKeyImpl ski;

            // new registrations

            while ((ski = newKeys.pollFirst()) != null) {

                if (ski.isValid()) {

                    growIfNeeded();

                    channelArray[totalChannels] = ski;

                    ski.setIndex(totalChannels);

                    pollWrapper.putEntry(totalChannels, ski);

                    totalChannels++;

                    MapEntry previous = fdMap.put(ski);

                    assert previous == null;

                }

            }

            // changes to interest ops

            while ((ski = updateKeys.pollFirst()) != null) {

                int events = ski.translateInterestOps();

                int fd = ski.getFDVal();

                if (ski.isValid() && fdMap.containsKey(fd)) {

                    int index = ski.getIndex();

                    assert index >= 0 && index < totalChannels;

                    pollWrapper.putEventOps(index, events);

                }

            }

        }

    }

    // Helper threads wait on this lock for the next poll.

    private final StartLock startLock = new StartLock();

    private final class StartLock {

        // A variable which distinguishes the current run of doSelect from the

        // previous one. Incrementing runsCounter and notifying threads will

        // trigger another round of poll.

        private long runsCounter;

       // Triggers threads, waiting on this lock to start polling.

        private synchronized void startThreads() {

            runsCounter++; // next run

            notifyAll(); // wake up threads.

        }

        // This function is called by a helper thread to wait for the

        // next round of poll(). It also checks, if this thread became

        // redundant. If yes, it returns true, notifying the thread

        // that it should exit.

        private synchronized boolean waitForStart(SelectThread thread) {

            while (true) {

                while (runsCounter == thread.lastRun) {

                    try {

                        startLock.wait();

                    } catch (InterruptedException e) {

                        Thread.currentThread().interrupt();

                    }

                }

                if (thread.isZombie()) { // redundant thread

                    return true; // will cause run() to exit.

                } else {

                    thread.lastRun = runsCounter; // update lastRun

                    return false; //   will cause run() to poll.

                }

            }

        }

    }

    // Main thread waits on this lock, until all helper threads are done

    // with poll().

    private final FinishLock finishLock = new FinishLock();

    private final class FinishLock  {

        // Number of helper threads, that did not finish yet.

        private int threadsToFinish;

        // IOException which occurred during the last run.

        IOException exception = null;

        // Called before polling.

        private void reset() {

            threadsToFinish = threads.size(); // helper threads

        }

        // Each helper thread invokes this function on finishLock, when

        // the thread is done with poll().

        private synchronized void threadFinished() {

            if (threadsToFinish == threads.size()) { // finished poll() first

                // if finished first, wakeup others

                wakeup();

            }

            threadsToFinish--;

            if (threadsToFinish == 0) // all helper threads finished poll().

                notify();             // notify the main thread

        }

        // The main thread invokes this function on finishLock to wait

        // for helper threads to finish poll().

        private synchronized void waitForHelperThreads() {

            if (threadsToFinish == threads.size()) {

                // no helper threads finished yet. Wakeup them up.

                wakeup();

            }

            while (threadsToFinish != 0) {

                try {

                    finishLock.wait();

                } catch (InterruptedException e) {

                    // Interrupted - set interrupted state.

                    Thread.currentThread().interrupt();

                }

            }

        }

        // sets IOException for this run

        private synchronized void setException(IOException e) {

            exception = e;

        }

        // Checks if there was any exception during the last run.

        // If yes, throws it

        private void checkForException() throws IOException {

            if (exception == null)

                return;

            StringBuffer message =  new StringBuffer("An exception occurred" +

                                       " during the execution of select(): \n");

            message.append(exception);

            message.append('\n');

            exception = null;

            throw new IOException(message.toString());

        }

    }

    private final class SubSelector {

        private final int pollArrayIndex; // starting index in pollArray to poll

        // These arrays will hold result of native select().

        // The first element of each array is the number of selected sockets.

        // Other elements are file descriptors of selected sockets.

        private final int[] readFds = new int [MAX_SELECTABLE_FDS + 1];

        private final int[] writeFds = new int [MAX_SELECTABLE_FDS + 1];

        private final int[] exceptFds = new int [MAX_SELECTABLE_FDS + 1];

        private SubSelector() {

            this.pollArrayIndex = 0; // main thread

        }

        private SubSelector(int threadIndex) { // helper threads

            this.pollArrayIndex = (threadIndex + 1) * MAX_SELECTABLE_FDS;

        }

        private int poll() throws IOException{ // poll for the main thread

            return poll0(pollWrapper.pollArrayAddress,

                         Math.min(totalChannels, MAX_SELECTABLE_FDS),

                         readFds, writeFds, exceptFds, timeout);

        }

        private int poll(int index) throws IOException {

            // poll for helper threads

            return  poll0(pollWrapper.pollArrayAddress +

                     (pollArrayIndex * PollArrayWrapper.SIZE_POLLFD),

                     Math.min(MAX_SELECTABLE_FDS,

                             totalChannels - (index + 1) * MAX_SELECTABLE_FDS),

                     readFds, writeFds, exceptFds, timeout);

        }

        private native int poll0(long pollAddress, int numfds,

             int[] readFds, int[] writeFds, int[] exceptFds, long timeout);

        private int processSelectedKeys(long updateCount, Consumer<SelectionKey> action) {

            int numKeysUpdated = 0;

            numKeysUpdated += processFDSet(updateCount, action, readFds,

                                           Net.POLLIN,

                                           false);

            numKeysUpdated += processFDSet(updateCount, action, writeFds,

                                           Net.POLLCONN |

                                           Net.POLLOUT,

                                           false);

            numKeysUpdated += processFDSet(updateCount, action, exceptFds,

                                           Net.POLLIN |

                                           Net.POLLCONN |

                                           Net.POLLOUT,

                                           true);

            return numKeysUpdated;

        }

        /**

         * updateCount is used to tell if a key has been counted as updated

         * in this select operation.

         *

         * me.updateCount <= updateCount

         */

        private int processFDSet(long updateCount,

                                 Consumer<SelectionKey> action,

                                 int[] fds, int rOps,

                                 boolean isExceptFds)

        {

            int numKeysUpdated = 0;

            for (int i = 1; i <= fds[0]; i++) {

                int desc = fds[i];

                if (desc == wakeupSourceFd) {

                    synchronized (interruptLock) {

                        interruptTriggered = true;

                    }

                    continue;

                }

                MapEntry me = fdMap.get(desc);

                // If me is null, the key was deregistered in the previous

                // processDeregisterQueue.

                if (me == null)

                    continue;

                SelectionKeyImpl sk = me.ski;

                // The descriptor may be in the exceptfds set because there is

                // OOB data queued to the socket. If there is OOB data then it

                // is discarded and the key is not added to the selected set.

                if (isExceptFds &&

                    discardUrgentData(desc))

                {

                    continue;

                }

                int updated = processReadyEvents(rOps, sk, action);

                if (updated > 0 && me.updateCount != updateCount) {

                    me.updateCount = updateCount;

                    numKeysUpdated++;

                }

            }

            return numKeysUpdated;

        }

    }

    // Represents a helper thread used for select.

    private final class SelectThread extends Thread {

        private final int index; // index of this thread

        final SubSelector subSelector;

        private long lastRun = 0; // last run number

        private volatile boolean zombie;

        // Creates a new thread

        private SelectThread(int i) {

            super(null, null, "SelectorHelper", 0, false);

            this.index = i;

            this.subSelector = new SubSelector(i);

            //make sure we wait for next round of poll

            this.lastRun = startLock.runsCounter;

        }

        void makeZombie() {

            zombie = true;

        }

        boolean isZombie() {

            return zombie;

        }

        public void run() {

            while (true) { // poll loop

                // wait for the start of poll. If this thread has become

                // redundant, then exit.

                if (startLock.waitForStart(this))

                    return;

                // call poll()

                try {

                    subSelector.poll(index);

                } catch (IOException e) {

                    // Save this exception and let other threads finish.

                    finishLock.setException(e);

                }

                // notify main thread, that this thread has finished, and

                // wakeup others, if this thread is the first to finish.

                finishLock.threadFinished();

            }

        }

    }

    // After some channels registered/deregistered, the number of required

    // helper threads may have changed. Adjust this number.

    private void adjustThreadsCount() {

        if (threadsCount > threads.size()) {

            // More threads needed. Start more threads.

            for (int i = threads.size(); i < threadsCount; i++) {

                SelectThread newThread = new SelectThread(i);

                threads.add(newThread);

                newThread.setDaemon(true);

                newThread.start();

            }

        } else if (threadsCount < threads.size()) {

            // Some threads become redundant. Remove them from the threads List.

            for (int i = threads.size() - 1 ; i >= threadsCount; i--)

                threads.remove(i).makeZombie();

        }

    }

    // Sets Windows wakeup socket to a signaled state.

    private void setWakeupSocket() {

        setWakeupSocket0(wakeupSinkFd);

    }

    private native void setWakeupSocket0(int wakeupSinkFd);

    // Sets Windows wakeup socket to a non-signaled state.

    private void resetWakeupSocket() {

        synchronized (interruptLock) {

            if (interruptTriggered == false)

                return;

            resetWakeupSocket0(wakeupSourceFd);

            interruptTriggered = false;

        }

    }

    private native void resetWakeupSocket0(int wakeupSourceFd);

    private native boolean discardUrgentData(int fd);

    // We increment this counter on each call to updateSelectedKeys()

    // each entry in  SubSelector.fdsMap has a memorized value of

    // updateCount. When we increment numKeysUpdated we set updateCount

    // for the corresponding entry to its current value. This is used to

    // avoid counting the same key more than once - the same key can

    // appear in readfds and writefds.

    private long updateCount = 0;

    // Update ops of the corresponding Channels. Add the ready keys to the

    // ready queue.

    private int updateSelectedKeys(Consumer<SelectionKey> action) {

        updateCount++;

        int numKeysUpdated = 0;

        numKeysUpdated += subSelector.processSelectedKeys(updateCount, action);

        for (SelectThread t: threads) {