/*
 * Copyright (c) 2005, 2007, 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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 * questions.
 */

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)
/**
 * 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;
    static final int NUM_EPOLLEVENTS  = Math.min(fdLimit(), 8192);

    // 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.
/**
     * 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
/**
     * 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
/**
     * 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
/**
     * Close epoll file descriptor and free poll array
     */
    void closeEPollFD() throws IOException {
        FileDispatcher.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.
/**
     * 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 {
        IOUtil.load();
        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 int fdLimit();
    private static native void interrupt(int fd);
    private static native void init();
}