/*

 * Copyright (c) 2005, 2009, 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

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 */

package sun.nio.ch;

import java.io.IOException;

import java.util.LinkedList;

import java.util.HashSet;

import java.util.Iterator;

/**

 * Manipulates a native array of epoll_event structs on Linux:

 *

 * typedef union epoll_data {

 *     void *ptr;

 *     int fd;

 *     __uint32_t u32;

 *     __uint64_t u64;

 *  } epoll_data_t;

 *

 * struct epoll_event {

 *     __uint32_t events;

 *     epoll_data_t data;

 * };

 *

 * The system call to wait for I/O events is epoll_wait(2). It populates an

 * array of epoll_event structures that are passed to the call. The data

 * member of the epoll_event structure contains the same data as was set

 * when the file descriptor was registered to epoll via epoll_ctl(2). In

 * this implementation we set data.fd to be the file descriptor that we

 * register. That way, we have the file descriptor available when we

 * process the events.

 *

 * All file descriptors registered with epoll have the POLLHUP and POLLERR

 * events enabled even when registered with an event set of 0. To ensure

 * that epoll_wait doesn't poll an idle file descriptor when the underlying

 * connection is closed or reset then its registration is deleted from

 * epoll (it will be re-added again if the event set is changed)

 */

class EPollArrayWrapper {

    // EPOLL_EVENTS

    static final int EPOLLIN      = 0x001;

    // opcodes

    static final int EPOLL_CTL_ADD      = 1;

    static final int EPOLL_CTL_DEL      = 2;

    static final int EPOLL_CTL_MOD      = 3;

    // Miscellaneous constants

    static final int SIZE_EPOLLEVENT  = sizeofEPollEvent();

    static final int EVENT_OFFSET     = 0;

    static final int DATA_OFFSET      = offsetofData();

    static final int FD_OFFSET        = DATA_OFFSET;

    // Base address of the native pollArray

    private final long pollArrayAddress;

    // Set of "idle" channels

    private final HashSet<SelChImpl> idleSet;

    EPollArrayWrapper() {

        // creates the epoll file descriptor

        epfd = epollCreate();

        // the epoll_event array passed to epoll_wait

        int allocationSize = NUM_EPOLLEVENTS * SIZE_EPOLLEVENT;

        pollArray = new AllocatedNativeObject(allocationSize, true);

        pollArrayAddress = pollArray.address();

        for (int i=0; i<NUM_EPOLLEVENTS; i++) {

            putEventOps(i, 0);

            putData(i, 0L);

        }

        // create idle set

        idleSet = new HashSet<SelChImpl>();

    }

    // Used to update file description registrations

    private static class Updator {

        SelChImpl channel;

        int opcode;

        int events;

        Updator(SelChImpl channel, int opcode, int events) {

            this.channel = channel;

            this.opcode = opcode;

            this.events = events;

        }

        Updator(SelChImpl channel, int opcode) {

            this(channel, opcode, 0);

        }

    }

    private LinkedList<Updator> updateList = new LinkedList<Updator>();

    // The epoll_event array for results from epoll_wait

    private AllocatedNativeObject pollArray;

    // The fd of the epoll driver

    final int epfd;

    // The fd of the interrupt line going out

    int outgoingInterruptFD;

    // The fd of the interrupt line coming in

    int incomingInterruptFD;

    // The index of the interrupt FD

    int interruptedIndex;

    // Number of updated pollfd entries

    int updated;

    void initInterrupt(int fd0, int fd1) {

        outgoingInterruptFD = fd1;

        incomingInterruptFD = fd0;

        epollCtl(epfd, EPOLL_CTL_ADD, fd0, EPOLLIN);

    }

    void putEventOps(int i, int event) {

        int offset = SIZE_EPOLLEVENT * i + EVENT_OFFSET;

        pollArray.putInt(offset, event);

    }

    void putData(int i, long value) {

        int offset = SIZE_EPOLLEVENT * i + DATA_OFFSET;

        pollArray.putLong(offset, value);

    }

    void putDescriptor(int i, int fd) {

        int offset = SIZE_EPOLLEVENT * i + FD_OFFSET;

        pollArray.putInt(offset, fd);

    }

    int getEventOps(int i) {

        int offset = SIZE_EPOLLEVENT * i + EVENT_OFFSET;

        return pollArray.getInt(offset);

    }

    int getDescriptor(int i) {

        int offset = SIZE_EPOLLEVENT * i + FD_OFFSET;

        return pollArray.getInt(offset);

    }

    /**

     * Update the events for a given channel.

     */

    void setInterest(SelChImpl channel, int mask) {

        synchronized (updateList) {

            // if the previous pending operation is to add this file descriptor

            // to epoll then update its event set

            if (updateList.size() > 0) {

                Updator last = updateList.getLast();

                if (last.channel == channel && last.opcode == EPOLL_CTL_ADD) {

                    last.events = mask;

                    return;

                }

            }

            // update existing registration

            updateList.add(new Updator(channel, EPOLL_CTL_MOD, mask));

        }

    }

    /**

     * Add a channel's file descriptor to epoll

     */

    void add(SelChImpl channel) {

        synchronized (updateList) {

            updateList.add(new Updator(channel, EPOLL_CTL_ADD));

        }

    }

    /**

     * Remove a channel's file descriptor from epoll

     */

    void release(SelChImpl channel) {

        synchronized (updateList) {

            // flush any pending updates

            for (Iterator<Updator> it = updateList.iterator(); it.hasNext();) {

                if (it.next().channel == channel) {

                    it.remove();

                }

            }

            // remove from the idle set (if present)

            idleSet.remove(channel);

            // remove from epoll (if registered)

            epollCtl(epfd, EPOLL_CTL_DEL, channel.getFDVal(), 0);

        }

    }

    /**

     * Close epoll file descriptor and free poll array

     */

    void closeEPollFD() throws IOException {

        FileDispatcherImpl.closeIntFD(epfd);

        pollArray.free();

    }

    int poll(long timeout) throws IOException {

        updateRegistrations();

        updated = epollWait(pollArrayAddress, NUM_EPOLLEVENTS, timeout, epfd);

        for (int i=0; i<updated; i++) {

            if (getDescriptor(i) == incomingInterruptFD) {

                interruptedIndex = i;

                interrupted = true;

                break;

            }

        }

        return updated;

    }

    /**

     * Update the pending registrations.

     */

    void updateRegistrations() {

        synchronized (updateList) {

            Updator u = null;

            while ((u = updateList.poll()) != null) {

                SelChImpl ch = u.channel;

                if (!ch.isOpen())

                    continue;

                // if the events are 0 then file descriptor is put into "idle

                // set" to prevent it being polled

                if (u.events == 0) {

                    boolean added = idleSet.add(u.channel);

                    // if added to idle set then remove from epoll if registered

                    if (added && (u.opcode == EPOLL_CTL_MOD))

                        epollCtl(epfd, EPOLL_CTL_DEL, ch.getFDVal(), 0);

                } else {

                    // events are specified. If file descriptor was in idle set

                    // it must be re-registered (by converting opcode to ADD)

                    boolean idle = false;

                    if (!idleSet.isEmpty())

                        idle = idleSet.remove(u.channel);

                    int opcode = (idle) ? EPOLL_CTL_ADD : u.opcode;

                    epollCtl(epfd, opcode, ch.getFDVal(), u.events);

                }

            }

        }

    }

    // interrupt support

    boolean interrupted = false;

    public void interrupt() {

        interrupt(outgoingInterruptFD);

    }

    public int interruptedIndex() {

        return interruptedIndex;

    }

    boolean interrupted() {

        return interrupted;

    }

    void clearInterrupted() {

        interrupted = false;

    }

    static {

        init();

    }

    private native int epollCreate();

    private native void epollCtl(int epfd, int opcode, int fd, int events);

    private native int epollWait(long pollAddress, int numfds, long timeout,

                                 int epfd) throws IOException;

    private static native int sizeofEPollEvent();

    private static native int offsetofData();

    private static native void interrupt(int fd);

    private static native void init();

}