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/*
 * Copyright (c) 2008, 2020 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0, which is available at
 * http://www.eclipse.org/legal/epl-2.0.
 *
 * This Source Code may also be made available under the following Secondary
 * Licenses when the conditions for such availability set forth in the
 * Eclipse Public License v. 2.0 are satisfied: GNU General Public License,
 * version 2 with the GNU Classpath Exception, which is available at
 * https://www.gnu.org/software/classpath/license.html.
 *
 * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
 */

package org.glassfish.grizzly.nio;

import java.io.IOException;
import java.nio.channels.ClosedChannelException;
import java.nio.channels.SelectableChannel;
import java.nio.channels.SelectionKey;
import java.nio.channels.Selector;
import java.util.Queue;
import java.util.Set;
import java.util.concurrent.TimeUnit;
import java.util.logging.Level;
import java.util.logging.Logger;

import org.glassfish.grizzly.CompletionHandler;
import org.glassfish.grizzly.Grizzly;
import org.glassfish.grizzly.impl.FutureImpl;
import org.glassfish.grizzly.impl.SafeFutureImpl;
import org.glassfish.grizzly.utils.Futures;

/**
 * Default implementation of NIO SelectorHandler
 *
 * @author Alexey Stashok
 */
public class DefaultSelectorHandler implements SelectorHandler {
    private static final long DEFAULT_SELECT_TIMEOUT_MILLIS = 30000;

    private static final Logger logger = Grizzly.logger(DefaultSelectorHandler.class);

    public static final boolean IS_WORKAROUND_SELECTOR_SPIN = Boolean.getBoolean(DefaultSelectorHandler.class.getName() + ".force-selector-spin-detection")
            || System.getProperty("os.name").equalsIgnoreCase("linux");

    protected final long selectTimeout;

    // Selector spin workaround artifacts

    /**
     * The threshold for detecting selector.select spin on linux, used for enabling workaround to prevent server from
     * hanging.
     */
    private static final int SPIN_RATE_THRESHOLD = 2000;

    // ----------------

    public DefaultSelectorHandler() {
        this(DEFAULT_SELECT_TIMEOUT_MILLIS, TimeUnit.MILLISECONDS);
    }

    public DefaultSelectorHandler(final long selectTimeout, final TimeUnit timeunit) {
        this.selectTimeout = TimeUnit.MILLISECONDS.convert(selectTimeout, timeunit);
    }

    @Override
    public long getSelectTimeout() {
        return selectTimeout;
    }

    @Override
    public boolean preSelect(final SelectorRunner selectorRunner) throws IOException {
        return processPendingTasks(selectorRunner);
    }

    @Override
    public Set select(final SelectorRunner selectorRunner) throws IOException {
        final Selector selector = selectorRunner.getSelector();
        final boolean hasPostponedTasks = !selectorRunner.getPostponedTasks().isEmpty();

        // The selector.select(...) returns the *new* SelectionKey count,
        // so it may return 0 even in the case, when there are unprocessed, but
        // ready SelectionKeys in the Selector's selected key set.
        if (!hasPostponedTasks) {
            selector.select(selectTimeout);
        } else {
            selector.selectNow();
        }

        final Set selectedKeys = selector.selectedKeys();

        if (IS_WORKAROUND_SELECTOR_SPIN) {
            selectorRunner.checkSelectorSpin(!selectedKeys.isEmpty() || hasPostponedTasks, SPIN_RATE_THRESHOLD);
        }

        return selectedKeys;
    }

    @Override
    public void postSelect(final SelectorRunner selectorRunner) throws IOException {
    }

    @Override
    public void registerKeyInterest(final SelectorRunner selectorRunner, final SelectionKey key, final int interest) throws IOException {
        if (isSelectorRunnerThread(selectorRunner)) {
            registerKey0(key, interest);
        } else {
            selectorRunner.addPendingTask(new RegisterKeyTask(key, interest));
        }
    }

    private static void registerKey0(final SelectionKey selectionKey, final int interest) {
        if (selectionKey.isValid()) {
            final int currentOps = selectionKey.interestOps();
            if ((currentOps & interest) != interest) {
                selectionKey.interestOps(currentOps | interest);
            }
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void deregisterKeyInterest(final SelectorRunner selectorRunner, final SelectionKey key, final int interest) throws IOException {
        if (key.isValid()) {
            final int currentOps = key.interestOps();
            if ((currentOps & interest) != 0) {
                key.interestOps(currentOps & ~interest);
            }
        }
    }

    @Override
    public void registerChannel(final SelectorRunner selectorRunner, final SelectableChannel channel, final int interest, final Object attachment)
            throws IOException {

        final FutureImpl future = SafeFutureImpl.create();

        registerChannelAsync(selectorRunner, channel, interest, attachment, Futures.toCompletionHandler(future));
        try {
            future.get(selectTimeout, TimeUnit.MILLISECONDS);
        } catch (Exception e) {
            throw new IOException(e.getMessage());
        }
    }

    @Override
    public void registerChannelAsync(SelectorRunner selectorRunner, SelectableChannel channel, int interest, Object attachment,
            CompletionHandler completionHandler) {

        if (isSelectorRunnerThread(selectorRunner)) {
            registerChannel0(selectorRunner, channel, interest, attachment, completionHandler);
        } else {
            addPendingTask(selectorRunner, new RegisterChannelOperation(channel, interest, attachment, completionHandler));
        }
    }

    @Override
    public void deregisterChannel(final SelectorRunner selectorRunner, final SelectableChannel channel) throws IOException {

        final FutureImpl future = SafeFutureImpl.create();

        deregisterChannelAsync(selectorRunner, channel, Futures.toCompletionHandler(future));
        try {
            future.get(selectTimeout, TimeUnit.MILLISECONDS);
        } catch (Exception e) {
            throw new IOException(e.getMessage());
        }
    }

    @Override
    public void deregisterChannelAsync(final SelectorRunner selectorRunner, final SelectableChannel channel,
            final CompletionHandler completionHandler) {

        if (isSelectorRunnerThread(selectorRunner)) {
            deregisterChannel0(selectorRunner, channel, completionHandler);
        } else {
            addPendingTask(selectorRunner, new DeregisterChannelOperation(channel, completionHandler));
        }
    }

    @Override
    public void execute(final SelectorRunner selectorRunner, final Task task, final CompletionHandler completionHandler) {
        if (isSelectorRunnerThread(selectorRunner)) {
            try {
                task.run();
                if (completionHandler != null) {
                    completionHandler.completed(task);
                }
            } catch (Exception e) {
                if (completionHandler != null) {
                    completionHandler.failed(e);
                }
            }
        } else {
            addPendingTask(selectorRunner, new RunnableTask(task, completionHandler));
        }
    }

    @Override
    public void enque(final SelectorRunner selectorRunner, final Task task, final CompletionHandler completionHandler) {

        if (isSelectorRunnerThread(selectorRunner)) {
            // If this is Selector thread - put the task to postponed queue
            // it's faster than using pending task queue, which is thread-safe
            final Queue postponedTasks = selectorRunner.getPostponedTasks();
            postponedTasks.offer(new RunnableTask(task, completionHandler));

        } else {
            addPendingTask(selectorRunner, new RunnableTask(task, completionHandler));
        }
    }

    private void addPendingTask(final SelectorRunner selectorRunner, final SelectorHandlerTask task) {

        if (selectorRunner == null) {
            task.cancel();
            return;
        }

        selectorRunner.addPendingTask(task);

        if (selectorRunner.isStop() && selectorRunner.getPendingTasks().remove(task)) {
            task.cancel();
        }
    }

    private boolean processPendingTasks(final SelectorRunner selectorRunner) throws IOException {

        return processPendingTaskQueue(selectorRunner, selectorRunner.obtainPostponedTasks())
                && (!selectorRunner.hasPendingTasks || processPendingTaskQueue(selectorRunner, selectorRunner.getPendingTasks()));
    }

    private boolean processPendingTaskQueue(final SelectorRunner selectorRunner, final Queue selectorHandlerTasks) throws IOException {
        SelectorHandlerTask selectorHandlerTask;
        while ((selectorHandlerTask = selectorHandlerTasks.poll()) != null) {
            if (!selectorHandlerTask.run(selectorRunner)) {
                return false;
            }
        }

        return true;
    }

    private static void registerChannel0(final SelectorRunner selectorRunner, final SelectableChannel channel, final int interest, final Object attachment,
            final CompletionHandler completionHandler) {

        try {
            if (channel.isOpen()) {

                final Selector selector = selectorRunner.getSelector();

                final SelectionKey key = channel.keyFor(selector);

                // Check whether the channel has been registered on a selector
                if (key == null || key.isValid()) {
                    // If channel is not registered or key is valid
                    final SelectionKey registeredSelectionKey = channel.register(selector, interest, attachment);

                    selectorRunner.getTransport().getSelectionKeyHandler().onKeyRegistered(registeredSelectionKey);

                    final RegisterChannelResult result = new RegisterChannelResult(selectorRunner, registeredSelectionKey, channel);

                    if (completionHandler != null) {
                        completionHandler.completed(result);
                    }
                } else {
                    // Channel has been registered already,
                    // but the key is not valid
                    final Queue postponedTasks = selectorRunner.getPostponedTasks();
                    final RegisterChannelOperation operation = new RegisterChannelOperation(channel, interest, attachment, completionHandler);

                    postponedTasks.add(operation);
                }
            } else {
                failChannelRegistration(completionHandler, new ClosedChannelException());
            }
        } catch (IOException e) {
            failChannelRegistration(completionHandler, e);
        }
    }

    private static void failChannelRegistration(final CompletionHandler completionHandler, final Throwable error) {

        if (completionHandler != null) {
            completionHandler.failed(error);
        }
    }

    private static void deregisterChannel0(final SelectorRunner selectorRunner, final SelectableChannel channel,
            final CompletionHandler completionHandler) {

        final Throwable error;
        try {
            if (channel.isOpen()) {

                final Selector selector = selectorRunner.getSelector();

                final SelectionKey key = channel.keyFor(selector);

                // Check whether the channel has been registered on a selector
                if (key != null) {
                    // If channel is registered
                    selectorRunner.getTransport().getSelectionKeyHandler().cancel(key);

                    selectorRunner.getTransport().getSelectionKeyHandler().onKeyDeregistered(key);

                    final RegisterChannelResult result = new RegisterChannelResult(selectorRunner, key, channel);

                    if (completionHandler != null) {
                        completionHandler.completed(result);
                    }
                    return;
                }

                error = new IllegalStateException("Channel is not registered");
            } else {
                error = new ClosedChannelException();
            }

            Futures.notifyFailure(null, completionHandler, error);
        } catch (IOException e) {
            Futures.notifyFailure(null, completionHandler, e);
        }
    }

    @Override
    public boolean onSelectorClosed(final SelectorRunner selectorRunner) {
        try {
            selectorRunner.workaroundSelectorSpin();
            return true;
        } catch (Exception e) {
            return false;
        }
    }

    private static boolean isSelectorRunnerThread(final SelectorRunner selectorRunner) {
        return selectorRunner != null && Thread.currentThread() == selectorRunner.getRunnerThread();
    }

    protected static final class RegisterKeyTask implements SelectorHandlerTask {
        private final SelectionKey selectionKey;
        private final int interest;

        public RegisterKeyTask(final SelectionKey selectionKey, final int interest) {
            this.selectionKey = selectionKey;
            this.interest = interest;
        }

        @Override
        public boolean run(final SelectorRunner selectorRunner) throws IOException {
            SelectionKey localSelectionKey = selectionKey;
            if (IS_WORKAROUND_SELECTOR_SPIN) {
                localSelectionKey = selectorRunner.checkIfSpinnedKey(selectionKey);
            }

            registerKey0(localSelectionKey, interest);

            return true;
        }

        @Override
        public void cancel() {
        }
    }

    protected static final class RegisterChannelOperation implements SelectorHandlerTask {
        private final SelectableChannel channel;
        private final int interest;
        private final Object attachment;
        private final CompletionHandler completionHandler;

        private RegisterChannelOperation(final SelectableChannel channel, final int interest, final Object attachment,
                final CompletionHandler completionHandler) {
            this.channel = channel;
            this.interest = interest;
            this.attachment = attachment;
            this.completionHandler = completionHandler;
        }

        @Override
        public boolean run(final SelectorRunner selectorRunner) throws IOException {
            registerChannel0(selectorRunner, channel, interest, attachment, completionHandler);
            return true;
        }

        @Override
        public void cancel() {
            if (completionHandler != null) {
                completionHandler.failed(new IOException("Selector is closed"));
            }
        }
    }

    protected static final class RunnableTask implements SelectorHandlerTask {
        private final Task task;
        private final CompletionHandler completionHandler;

        private RunnableTask(final Task task, final CompletionHandler completionHandler) {
            this.task = task;
            this.completionHandler = completionHandler;
        }

        @Override
        public boolean run(final SelectorRunner selectorRunner) throws IOException {
            boolean continueExecution = true;

            try {
                continueExecution = task.run();
                if (completionHandler != null) {
                    completionHandler.completed(task);
                }
            } catch (Throwable t) {
                logger.log(Level.FINEST, "doExecutePendiongIO failed.", t);

                if (completionHandler != null) {
                    completionHandler.failed(t);
                }
            }

            return continueExecution;
        }

        @Override
        public void cancel() {
            if (completionHandler != null) {
                completionHandler.failed(new IOException("Selector is closed"));
            }
        }
    }

    protected static final class DeregisterChannelOperation implements SelectorHandlerTask {
        private final SelectableChannel channel;
        private final CompletionHandler completionHandler;

        private DeregisterChannelOperation(final SelectableChannel channel, final CompletionHandler completionHandler) {
            this.channel = channel;
            this.completionHandler = completionHandler;
        }

        @Override
        public boolean run(final SelectorRunner selectorRunner) throws IOException {
            deregisterChannel0(selectorRunner, channel, completionHandler);
            return true;
        }

        @Override
        public void cancel() {
            if (completionHandler != null) {
                completionHandler.failed(new IOException("Selector is closed"));
            }
        }
    }
}