/*

 * Copyright (c) 2008, 2013, Oracle and/or its affiliates. All rights reserved.

 * Copyright 2012 SAP AG. 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.HashSet;

import java.util.Iterator;

import java.util.concurrent.ArrayBlockingQueue;

import java.util.concurrent.RejectedExecutionException;

import java.util.concurrent.atomic.AtomicInteger;

import java.util.concurrent.locks.ReentrantLock;

import sun.misc.Unsafe;

/**

 * AsynchronousChannelGroup implementation based on the AIX pollset framework.

 */

final class AixPollPort

    extends Port

{

    private static final Unsafe unsafe = Unsafe.getUnsafe();

    static {

        IOUtil.load();

        init();

    }

    /**

     * struct pollfd {

     *     int fd;

     *     short events;

     *     short revents;

     * }

     */

    private static final int SIZEOF_POLLFD    = eventSize();

    private static final int OFFSETOF_EVENTS  = eventsOffset();

    private static final int OFFSETOF_REVENTS = reventsOffset();

    private static final int OFFSETOF_FD      = fdOffset();

    // opcodes

    private static final int PS_ADD     = 0x0;

    private static final int PS_MOD     = 0x1;

    private static final int PS_DELETE  = 0x2;

    // maximum number of events to poll at a time

    private static final int MAX_POLL_EVENTS = 512;

    // pollset ID

    private final int pollset;

    // true if port is closed

    private boolean closed;

    // socket pair used for wakeup

    private final int sp[];

    // socket pair used to indicate pending pollsetCtl calls

    // Background info: pollsetCtl blocks when another thread is in a pollsetPoll call.

    private final int ctlSp[];

    // number of wakeups pending

    private final AtomicInteger wakeupCount = new AtomicInteger();

    // address of the poll array passed to pollset_poll

    private final long address;

    // 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);

    // encapsulates a pollset control event for a file descriptor

    static class ControlEvent {

        final int fd;

        final int events;

        final boolean removeOnly;

        int error = 0;

        ControlEvent(int fd, int events, boolean removeOnly) {

            this.fd = fd;

            this.events = events;

            this.removeOnly = removeOnly;

        }

        int fd()                 { return fd; }

        int events()             { return events; }

        boolean removeOnly()     { return removeOnly; }

        int error()              { return error; }

        void setError(int error) { this.error = error; }

    }

    // queue of control events that need to be processed

    // (this object is also used for synchronization)

    private final HashSet<ControlEvent> controlQueue = new HashSet<ControlEvent>();

    // lock used to check whether a poll operation is ongoing

    private final ReentrantLock controlLock = new ReentrantLock();

    AixPollPort(AsynchronousChannelProvider provider, ThreadPool pool)

        throws IOException

    {

        super(provider, pool);

        // open pollset

        this.pollset = pollsetCreate();

        // create socket pair for wakeup mechanism

        int[] sv = new int[2];

        try {

            socketpair(sv);

            // register one end with pollset

        } catch (IOException x) {

            pollsetDestroy(pollset);

            throw x;

        }

        this.sp = sv;

        // create socket pair for pollset control mechanism

        sv = new int[2];

        try {

            socketpair(sv);

            // register one end with pollset

        } catch (IOException x) {

            pollsetDestroy(pollset);

            throw x;

        }

        this.ctlSp = sv;

        // allocate the poll array

        this.address = allocatePollArray(MAX_POLL_EVENTS);

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

        // threads polls

        this.queue = new ArrayBlockingQueue<Event>(MAX_POLL_EVENTS);

        this.queue.offer(NEED_TO_POLL);

    }

    AixPollPort start() {

        startThreads(new EventHandlerTask());

        return this;

    }

    /**

     * Release all resources

     */

    private void implClose() {

        synchronized (this) {

            if (closed)

                return;

            closed = true;

        }

        freePollArray(address);

        close0(sp[0]);

        close0(sp[1]);

        close0(ctlSp[0]);

        close0(ctlSp[1]);

        pollsetDestroy(pollset);

    }

    private void wakeup() {

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

            // write byte to socketpair to force wakeup

            try {

                interrupt(sp[1]);

            } 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) {

        queueControlEvent(new ControlEvent(fd, events, false));

    }

    // Callback method for implementations that need special handling when fd is removed

    @Override

    protected void preUnregister(int fd) {

        queueControlEvent(new ControlEvent(fd, 0, true));

    }

    // Add control event into queue and wait for completion.

    // In case the control lock is free, this method also tries to apply the control change directly.

    private void queueControlEvent(ControlEvent ev) {

        // pollsetCtl blocks when a poll call is ongoing. This is very probable.

        // Therefore we let the polling thread do the pollsetCtl call.

        synchronized (controlQueue) {

            controlQueue.add(ev);

            // write byte to socketpair to force wakeup

            try {

                interrupt(ctlSp[1]);

            } catch (IOException x) {

                throw new AssertionError(x);

            }

            do {

                // Directly empty queue if no poll call is ongoing.

                if (controlLock.tryLock()) {

                    try {

                        processControlQueue();

                    } finally {

                        controlLock.unlock();

                    }

                } else {

                    try {

                        // Do not starve in case the polling thread returned before

                        // we could write to ctlSp[1] but the polling thread did not

                        // release the control lock until we checked. Therefore, use

                        // a timed wait for the time being.

                        controlQueue.wait(100);

                    } catch (InterruptedException e) {

                        // ignore exception and try again

                    }

                }

            } while (controlQueue.contains(ev));

        }

        if (ev.error() != 0) {

            throw new AssertionError();

        }

    }

    // Process all events currently stored in the control queue.

    private void processControlQueue() {

        synchronized (controlQueue) {

            // On Aix it is only possible to set the event

            // bits on the first call of pollsetCtl. Later

            // calls only add bits, but cannot remove them.

            // Therefore, we always remove the file

            // descriptor ignoring the error and then add it.

            Iterator<ControlEvent> iter = controlQueue.iterator();

            while (iter.hasNext()) {

                ControlEvent ev = iter.next();

                pollsetCtl(pollset, PS_DELETE, ev.fd(), 0);

                if (!ev.removeOnly()) {

                    ev.setError(pollsetCtl(pollset, PS_MOD, ev.fd(), ev.events()));

                }

                iter.remove();

            }

            controlQueue.notifyAll();

        }

    }

    /*

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

     * onEvent handler.

     *

     * Events are retreived from pollset 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 (;;) {

                    int n;

                    controlLock.lock();

                    try {

                        n = pollsetPoll(pollset, address, MAX_POLL_EVENTS);

                    } finally {

                        controlLock.unlock();

                    }

                    /*

                     * '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) {

                            long eventAddress = getEvent(address, n);

                            int fd = getDescriptor(eventAddress);

                            // To emulate one shot semantic we need to remove

                            // the file descriptor here.

                            pollsetCtl(pollset, PS_DELETE, fd, 0);

                            // wakeup

                            if (fd == sp[0]) {

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

                                    // no more wakeups so drain pipe

                                    drain1(sp[0]);

                                }

                                // This is the only file descriptor without

                                // one shot semantic => register it again.

                                // 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;

                            }

                            // wakeup to process control event

                            if (fd == ctlSp[0]) {

                                synchronized (controlQueue) {

                                    drain1(ctlSp[0]);

                                    // This file descriptor does not have

                                    // one shot semantic => register it again.

                                    processControlQueue();

                                }

                                continue;

                            }

                            PollableChannel channel = fdToChannel.get(fd);

                            if (channel != null) {

                                int events = getRevents(eventAddress);

                                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();

                }

            }

        }

    }

    /**

     * Allocates a poll array to handle up to {@code count} events.

     */

    private static long allocatePollArray(int count) {

        return unsafe.allocateMemory(count * SIZEOF_POLLFD);

    }

    /**

     * Free a poll array

     */

    private static void freePollArray(long address) {

        unsafe.freeMemory(address);

    }

    /**

     * Returns event[i];

     */

    private static long getEvent(long address, int i) {

        return address + (SIZEOF_POLLFD*i);

    }

    /**

     * Returns event->fd

     */

    private static int getDescriptor(long eventAddress) {

        return unsafe.getInt(eventAddress + OFFSETOF_FD);

    }

    /**

     * Returns event->events

     */

    private static int getEvents(long eventAddress) {

        return unsafe.getChar(eventAddress + OFFSETOF_EVENTS);

    }

    /**

     * Returns event->revents

     */

    private static int getRevents(long eventAddress) {

        return unsafe.getChar(eventAddress + OFFSETOF_REVENTS);

    }

    // -- Native methods --

    private static native void init();

    private static native int eventSize();

    private static native int eventsOffset();

    private static native int reventsOffset();

    private static native int fdOffset();

    private static native int pollsetCreate() throws IOException;

    private static native int pollsetCtl(int pollset, int opcode, int fd, int events);

    private static native int pollsetPoll(int pollset, long pollAddress, int numfds)

        throws IOException;

    private static native void pollsetDestroy(int pollset);