/*

 * Copyright (c) 2005, 2016, 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.security.AccessController;

import java.util.BitSet;

import java.util.HashMap;

import java.util.Map;

import sun.security.action.GetIntegerAction;

/**

 * 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.

 */

class EPollArrayWrapper {

    // EPOLL_EVENTS

    private static final int EPOLLIN      = 0x001;

    // opcodes

    private static final int EPOLL_CTL_ADD      = 1;

    private static final int EPOLL_CTL_DEL      = 2;

    private static final int EPOLL_CTL_MOD      = 3;

    // Miscellaneous constants

    private static final int SIZE_EPOLLEVENT  = sizeofEPollEvent();

    private static final int EVENT_OFFSET     = 0;

    private static final int DATA_OFFSET      = offsetofData();

    private static final int FD_OFFSET        = DATA_OFFSET;

    private static final int OPEN_MAX         = IOUtil.fdLimit();

    private static final int NUM_EPOLLEVENTS  = Math.min(OPEN_MAX, 8192);

    // Special value to indicate that an update should be ignored

    private static final byte  KILLED = (byte)-1;

    // Initial size of arrays for fd registration changes

    private static final int INITIAL_PENDING_UPDATE_SIZE = 64;

    // maximum size of updatesLow

    private static final int MAX_UPDATE_ARRAY_SIZE = AccessController.doPrivileged(

        new GetIntegerAction("sun.nio.ch.maxUpdateArraySize", Math.min(OPEN_MAX, 64*1024)));

    // The fd of the epoll driver

    private final int epfd;

     // The epoll_event array for results from epoll_wait

    private final AllocatedNativeObject pollArray;

    // Base address of the epoll_event array

    private final long pollArrayAddress;

    // The fd of the interrupt line going out

    private int outgoingInterruptFD;

    // The fd of the interrupt line coming in

    private int incomingInterruptFD;

    // The index of the interrupt FD

    private int interruptedIndex;

    // Number of updated pollfd entries

    int updated;

    // object to synchronize fd registration changes

    private final Object updateLock = new Object();

    // number of file descriptors with registration changes pending

    private int updateCount;

    // file descriptors with registration changes pending

    private int[] updateDescriptors = new int[INITIAL_PENDING_UPDATE_SIZE];

    // events for file descriptors with registration changes pending, indexed

    // by file descriptor and stored as bytes for efficiency reasons. For

    // file descriptors higher than MAX_UPDATE_ARRAY_SIZE (unlimited case at

    // least) then the update is stored in a map.

    private final byte[] eventsLow = new byte[MAX_UPDATE_ARRAY_SIZE];

    private final Map<Integer,Byte> eventsHigh = new HashMap<>();

    // Used by release and updateRegistrations to track whether a file

    // descriptor is registered with epoll.

    private final BitSet registered = new BitSet();

    EPollArrayWrapper() throws IOException {

        // 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();

    }

    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 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);

    }

    /**

     * Returns {@code true} if updates for the given key (file

     * descriptor) are killed.

     */

    private boolean isEventsHighKilled(Integer key) {

        assert key >= MAX_UPDATE_ARRAY_SIZE;

        Byte value = eventsHigh.get(key);

        return (value != null && value == KILLED);

    }

    /**

     * Sets the pending update events for the given file descriptor. This

     * method has no effect if the update events is already set to KILLED,

     * unless {@code force} is {@code true}.

     */

    private void setUpdateEvents(int fd, byte events, boolean force) {

        if (fd < MAX_UPDATE_ARRAY_SIZE) {

            if ((eventsLow[fd] != KILLED) || force) {

                eventsLow[fd] = events;

            }

        } else {

            Integer key = Integer.valueOf(fd);

            if (!isEventsHighKilled(key) || force) {

                eventsHigh.put(key, Byte.valueOf(events));

            }

        }

    }

    /**

     * Returns the pending update events for the given file descriptor.

     */

    private byte getUpdateEvents(int fd) {

        if (fd < MAX_UPDATE_ARRAY_SIZE) {

            return eventsLow[fd];

        } else {

            Byte result = eventsHigh.get(Integer.valueOf(fd));

            // result should never be null

            return result.byteValue();

        }

    }

    /**

     * Update the events for a given file descriptor

     */

    void setInterest(int fd, int mask) {

        synchronized (updateLock) {

            // record the file descriptor and events

            int oldCapacity = updateDescriptors.length;

            if (updateCount == oldCapacity) {

                int newCapacity = oldCapacity + INITIAL_PENDING_UPDATE_SIZE;

                int[] newDescriptors = new int[newCapacity];

                System.arraycopy(updateDescriptors, 0, newDescriptors, 0, oldCapacity);

                updateDescriptors = newDescriptors;

            }

            updateDescriptors[updateCount++] = fd;

            // events are stored as bytes for efficiency reasons

            byte b = (byte)mask;

            assert (b == mask) && (b != KILLED);

            setUpdateEvents(fd, b, false);

        }

    }

    /**

     * Add a file descriptor

     */

    void add(int fd) {

        // force the initial update events to 0 as it may be KILLED by a

        // previous registration.

        synchronized (updateLock) {

            assert !registered.get(fd);

            setUpdateEvents(fd, (byte)0, true);

        }

    }

    /**

     * Remove a file descriptor

     */

    void remove(int fd) {

        synchronized (updateLock) {

            // kill pending and future update for this file descriptor

            setUpdateEvents(fd, KILLED, false);

            // remove from epoll

            if (registered.get(fd)) {

                epollCtl(epfd, EPOLL_CTL_DEL, fd, 0);

                registered.clear(fd);

            }

        }

    }

    /**

     * 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.

     */

    private void updateRegistrations() {

        synchronized (updateLock) {

            int j = 0;

            while (j < updateCount) {

                int fd = updateDescriptors[j];

                short events = getUpdateEvents(fd);

                boolean isRegistered = registered.get(fd);

                int opcode = 0;

                if (events != KILLED) {

                    if (isRegistered) {

                        opcode = (events != 0) ? EPOLL_CTL_MOD : EPOLL_CTL_DEL;

                    } else {

                        opcode = (events != 0) ? EPOLL_CTL_ADD : 0;

                    }

                    if (opcode != 0) {

                        epollCtl(epfd, opcode, fd, events);

                        if (opcode == EPOLL_CTL_ADD) {

                            registered.set(fd);

                        } else if (opcode == EPOLL_CTL_DEL) {

                            registered.clear(fd);

                        }

                    }

                }

                j++;

            }

            updateCount = 0;

        }

    }

    // interrupt support

    private 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 void interrupt(int fd);

    private static native void init();

}