/*

 * Copyright (c) 2008, 2018, 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 sun.nio.ch;

import java.nio.channels.spi.AsynchronousChannelProvider;

import java.io.IOException;

import java.util.concurrent.ArrayBlockingQueue;

import java.util.concurrent.RejectedExecutionException;

import java.util.concurrent.atomic.AtomicInteger;

/**

 * AsynchronousChannelGroup implementation based on the Linux epoll facility.

 */

final class EPollPort

    extends Port

{

    // maximum number of events to poll at a time

    private static final int MAX_EPOLL_EVENTS = 512;

    // errors

    private static final int ENOENT     = 2;

    // epoll file descriptor

    private final int epfd;

    // true if epoll closed

    private boolean closed;

    // socket pair used for wakeup

    private final int sp[];

    // number of wakeups pending

    private final AtomicInteger wakeupCount = new AtomicInteger();

    // encapsulates an event for a channel

    static class Event {

        final PollableChannel channel;

        final int events;

        Event(PollableChannel channel, int events) {

            this.channel = channel;

            this.events = events;

        }

        PollableChannel channel()   { return channel; }

        int events()                { return events; }

    }

    // queue of events for cases that a polling thread dequeues more than one

    // event

    private final ArrayBlockingQueue<Event> queue;

    private final Event NEED_TO_POLL = new Event(null, 0);

    private final Event EXECUTE_TASK_OR_SHUTDOWN = new Event(null, 0);

    EPollPort(AsynchronousChannelProvider provider, ThreadPool pool)

        throws IOException

    {

        super(provider, pool);

        // create socket pair for wakeup mechanism

        try {

        }

        // create the queue and offer the special event to ensure that the first

        // threads polls

        this.queue = new ArrayBlockingQueue<>(MAX_EPOLL_EVENTS);

        this.queue.offer(NEED_TO_POLL);

    }

    EPollPort start() {

        startThreads(new EventHandlerTask());

        return this;

    }

    /**

     * Release all resources

     */

    private void implClose() {

        synchronized (this) {

            if (closed)

                return;

            closed = true;

        }

    }

    private void wakeup() {

        if (wakeupCount.incrementAndGet() == 1) {

            // write byte to socketpair to force wakeup

            try {

            } catch (IOException x) {

                throw new AssertionError(x);

            }

        }

    }

    @Override

    void executeOnHandlerTask(Runnable task) {

        synchronized (this) {

            if (closed)

                throw new RejectedExecutionException();

            offerTask(task);

            wakeup();

        }

    }

    @Override

    void shutdownHandlerTasks() {

        /*

         * If no tasks are running then just release resources; otherwise

         * write to the one end of the socketpair to wakeup any polling threads.

         */

        int nThreads = threadCount();

        if (nThreads == 0) {

            implClose();

        } else {

            // send interrupt to each thread

            while (nThreads-- > 0) {

                wakeup();

            }

        }

    }

    // invoke by clients to register a file descriptor

    @Override

    void startPoll(int fd, int events) {

        // update events (or add to epoll on first usage)

        if (err == ENOENT)

        if (err != 0)

            throw new AssertionError();     // should not happen

    }

    /*

     * Task to process events from epoll and dispatch to the channel's

     * onEvent handler.

     *

     * Events are retreived from epoll in batch and offered to a BlockingQueue

     * where they are consumed by handler threads. A special "NEED_TO_POLL"

     * event is used to signal one consumer to re-poll when all events have

     * been consumed.

     */

    private class EventHandlerTask implements Runnable {

        private Event poll() throws IOException {

            try {

                for (;;) {

                    /*

                     * 'n' events have been read. Here we map them to their

                     * corresponding channel in batch and queue n-1 so that

                     * they can be handled by other handler threads. The last

                     * event is handled by this thread (and so is not queued).

                     */

                    fdToChannelLock.readLock().lock();

                    try {

                        while (n-- > 0) {

                            // wakeup

                            if (fd == sp[0]) {

                                if (wakeupCount.decrementAndGet() == 0) {

                                    // no more wakeups so drain pipe

                                }

                                // queue special event if there are more events

                                // to handle.

                                if (n > 0) {

                                    queue.offer(EXECUTE_TASK_OR_SHUTDOWN);

                                    continue;

                                }

                                return EXECUTE_TASK_OR_SHUTDOWN;

                            }

                            PollableChannel channel = fdToChannel.get(fd);

                            if (channel != null) {

                                Event ev = new Event(channel, events);

                                // n-1 events are queued; This thread handles

                                // the last one except for the wakeup

                                if (n > 0) {

                                    queue.offer(ev);

                                } else {

                                    return ev;

                                }

                            }

                        }

                    } finally {

                        fdToChannelLock.readLock().unlock();

                    }

                }

            } finally {

                // to ensure that some thread will poll when all events have

                // been consumed

                queue.offer(NEED_TO_POLL);

            }

        }

        public void run() {

            Invoker.GroupAndInvokeCount myGroupAndInvokeCount =

                Invoker.getGroupAndInvokeCount();

            final boolean isPooledThread = (myGroupAndInvokeCount != null);

            boolean replaceMe = false;

            Event ev;

            try {

                for (;;) {

                    // reset invoke count

                    if (isPooledThread)

                        myGroupAndInvokeCount.resetInvokeCount();

                    try {

                        replaceMe = false;

                        ev = queue.take();

                        // no events and this thread has been "selected" to

                        // poll for more.

                        if (ev == NEED_TO_POLL) {

                            try {

                                ev = poll();

                            } catch (IOException x) {

                                x.printStackTrace();

                                return;

                            }

                        }

                    } catch (InterruptedException x) {

                        continue;

                    }

                    // handle wakeup to execute task or shutdown

                    if (ev == EXECUTE_TASK_OR_SHUTDOWN) {

                        Runnable task = pollTask();

                        if (task == null) {

                            // shutdown request

                            return;

                        }

                        // run task (may throw error/exception)

                        replaceMe = true;

                        task.run();

                        continue;

                    }

                    // process event

                    try {

                        ev.channel().onEvent(ev.events(), isPooledThread);

                    } catch (Error x) {

                        replaceMe = true; throw x;

                    } catch (RuntimeException x) {

                        replaceMe = true; throw x;

                    }

                }

            } finally {

                // last handler to exit when shutdown releases resources

                int remaining = threadExit(this, replaceMe);

                if (remaining == 0 && isShutdown()) {

                    implClose();

                }

            }

        }

    }

}