/*

 * Copyright (c) 2000, 2017, 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.io.FileDescriptor;

import java.lang.reflect.Constructor;

import java.lang.reflect.InvocationTargetException;

import java.nio.ByteBuffer;

import java.nio.MappedByteBuffer;

import java.security.AccessController;

import java.security.PrivilegedAction;

import java.util.Collection;

import java.util.Iterator;

import java.util.Set;

import jdk.internal.misc.Unsafe;

import sun.security.action.GetPropertyAction;

public class Util {

    // -- Caches --

    // The number of temp buffers in our pool

    private static final int TEMP_BUF_POOL_SIZE = IOUtil.IOV_MAX;

    // The max size allowed for a cached temp buffer, in bytes

    private static final long MAX_CACHED_BUFFER_SIZE = getMaxCachedBufferSize();

    // Per-thread cache of temporary direct buffers

    private static ThreadLocal<BufferCache> bufferCache =

        new ThreadLocal<BufferCache>()

    {

        @Override

        protected BufferCache initialValue() {

            return new BufferCache();

        }

    };

    /**

     * Returns the max size allowed for a cached temp buffers, in

     * bytes. It defaults to Long.MAX_VALUE. It can be set with the

     * jdk.nio.maxCachedBufferSize property. Even though

     * ByteBuffer.capacity() returns an int, we're using a long here

     * for potential future-proofing.

     */

    private static long getMaxCachedBufferSize() {

        String s = GetPropertyAction

                .privilegedGetProperty("jdk.nio.maxCachedBufferSize");

        if (s != null) {

            try {

                long m = Long.parseLong(s);

                if (m >= 0) {

                    return m;

                } else {

                    // if it's negative, ignore the system property

                }

            } catch (NumberFormatException e) {

                // if the string is not well formed, ignore the system property

            }

        }

        return Long.MAX_VALUE;

    }

    /**

     * Returns true if a buffer of this size is too large to be

     * added to the buffer cache, false otherwise.

     */

    private static boolean isBufferTooLarge(int size) {

        return size > MAX_CACHED_BUFFER_SIZE;

    }

    /**

     * Returns true if the buffer is too large to be added to the

     * buffer cache, false otherwise.

     */

    private static boolean isBufferTooLarge(ByteBuffer buf) {

        return isBufferTooLarge(buf.capacity());

    }

    /**

     * A simple cache of direct buffers.

     */

    private static class BufferCache {

        // the array of buffers

        private ByteBuffer[] buffers;

        // the number of buffers in the cache

        private int count;

        // the index of the first valid buffer (undefined if count == 0)

        private int start;

        private int next(int i) {

            return (i + 1) % TEMP_BUF_POOL_SIZE;

        }

        BufferCache() {

            buffers = new ByteBuffer[TEMP_BUF_POOL_SIZE];

        }

        /**

         * Removes and returns a buffer from the cache of at least the given

         * size (or null if no suitable buffer is found).

         */

        ByteBuffer get(int size) {

            // Don't call this if the buffer would be too large.

            assert !isBufferTooLarge(size);

            if (count == 0)

                return null;  // cache is empty

            ByteBuffer[] buffers = this.buffers;

            // search for suitable buffer (often the first buffer will do)

            ByteBuffer buf = buffers[start];

            if (buf.capacity() < size) {

                buf = null;

                int i = start;

                while ((i = next(i)) != start) {

                    ByteBuffer bb = buffers[i];

                    if (bb == null)

                        break;

                    if (bb.capacity() >= size) {

                        buf = bb;

                        break;

                    }

                }

                if (buf == null)

                    return null;

                // move first element to here to avoid re-packing

                buffers[i] = buffers[start];

            }

            // remove first element

            buffers[start] = null;

            start = next(start);

            count--;

            // prepare the buffer and return it

            buf.rewind();

            buf.limit(size);

            return buf;

        }

        boolean offerFirst(ByteBuffer buf) {

            // Don't call this if the buffer is too large.

            assert !isBufferTooLarge(buf);

            if (count >= TEMP_BUF_POOL_SIZE) {

                return false;

            } else {

                start = (start + TEMP_BUF_POOL_SIZE - 1) % TEMP_BUF_POOL_SIZE;

                buffers[start] = buf;

                count++;

                return true;

            }

        }

        boolean offerLast(ByteBuffer buf) {

            // Don't call this if the buffer is too large.

            assert !isBufferTooLarge(buf);

            if (count >= TEMP_BUF_POOL_SIZE) {

                return false;

            } else {

                int next = (start + count) % TEMP_BUF_POOL_SIZE;

                buffers[next] = buf;

                count++;

                return true;

            }

        }

        boolean isEmpty() {

            return count == 0;

        }

        ByteBuffer removeFirst() {

            assert count > 0;

            ByteBuffer buf = buffers[start];

            buffers[start] = null;

            start = next(start);

            count--;

            return buf;

        }

    }

    /**

     * Returns a temporary buffer of at least the given size

     */

    public static ByteBuffer getTemporaryDirectBuffer(int size) {

        // If a buffer of this size is too large for the cache, there

        // should not be a buffer in the cache that is at least as

        // large. So we'll just create a new one. Also, we don't have

        // to remove the buffer from the cache (as this method does

        // below) given that we won't put the new buffer in the cache.

        if (isBufferTooLarge(size)) {

            return ByteBuffer.allocateDirect(size);

        }

        BufferCache cache = bufferCache.get();

        ByteBuffer buf = cache.get(size);

        if (buf != null) {

            return buf;

        } else {

            // No suitable buffer in the cache so we need to allocate a new

            // one. To avoid the cache growing then we remove the first

            // buffer from the cache and free it.

            if (!cache.isEmpty()) {

                buf = cache.removeFirst();

                free(buf);

            }

            return ByteBuffer.allocateDirect(size);

        }

    }

    /**

     * Releases a temporary buffer by returning to the cache or freeing it.

     */

    public static void releaseTemporaryDirectBuffer(ByteBuffer buf) {

        offerFirstTemporaryDirectBuffer(buf);

    }

    /**

     * Releases a temporary buffer by returning to the cache or freeing it. If

     * returning to the cache then insert it at the start so that it is

     * likely to be returned by a subsequent call to getTemporaryDirectBuffer.

     */

    static void offerFirstTemporaryDirectBuffer(ByteBuffer buf) {

        // If the buffer is too large for the cache we don't have to

        // check the cache. We'll just free it.

        if (isBufferTooLarge(buf)) {

            free(buf);

            return;

        }

        assert buf != null;

        BufferCache cache = bufferCache.get();

        if (!cache.offerFirst(buf)) {

            // cache is full

            free(buf);

        }

    }

    /**

     * Releases a temporary buffer by returning to the cache or freeing it. If

     * returning to the cache then insert it at the end. This makes it

     * suitable for scatter/gather operations where the buffers are returned to

     * cache in same order that they were obtained.

     */

    static void offerLastTemporaryDirectBuffer(ByteBuffer buf) {

        // If the buffer is too large for the cache we don't have to

        // check the cache. We'll just free it.

        if (isBufferTooLarge(buf)) {

            free(buf);

            return;

        }

        assert buf != null;

        BufferCache cache = bufferCache.get();

        if (!cache.offerLast(buf)) {

            // cache is full

            free(buf);

        }

    }

    /**

     * Frees the memory for the given direct buffer

     */

    private static void free(ByteBuffer buf) {

        ((DirectBuffer)buf).cleaner().clean();

    }

    // -- Random stuff --

    static ByteBuffer[] subsequence(ByteBuffer[] bs, int offset, int length) {

        if ((offset == 0) && (length == bs.length))

            return bs;

        int n = length;

        ByteBuffer[] bs2 = new ByteBuffer[n];

        for (int i = 0; i < n; i++)

            bs2[i] = bs[offset + i];

        return bs2;

    }

    static <E> Set<E> ungrowableSet(final Set<E> s) {

        return new Set<E>() {

                public int size()                 { return s.size(); }

                public boolean isEmpty()          { return s.isEmpty(); }

                public boolean contains(Object o) { return s.contains(o); }

                public Object[] toArray()         { return s.toArray(); }

                public <T> T[] toArray(T[] a)     { return s.toArray(a); }

                public String toString()          { return s.toString(); }

                public Iterator<E> iterator()     { return s.iterator(); }

                public boolean equals(Object o)   { return s.equals(o); }

                public int hashCode()             { return s.hashCode(); }

                public void clear()               { s.clear(); }

                public boolean remove(Object o)   { return s.remove(o); }

                public boolean containsAll(Collection<?> coll) {

                    return s.containsAll(coll);

                }

                public boolean removeAll(Collection<?> coll) {

                    return s.removeAll(coll);

                }

                public boolean retainAll(Collection<?> coll) {

                    return s.retainAll(coll);

                }

                public boolean add(E o){

                    throw new UnsupportedOperationException();

                }

                public boolean addAll(Collection<? extends E> coll) {

                    throw new UnsupportedOperationException();

                }

        };

    }

    // -- Unsafe access --

    private static Unsafe unsafe = Unsafe.getUnsafe();

    private static byte _get(long a) {

        return unsafe.getByte(a);

    }

    private static void _put(long a, byte b) {

        unsafe.putByte(a, b);

    }

    static void erase(ByteBuffer bb) {

        unsafe.setMemory(((DirectBuffer)bb).address(), bb.capacity(), (byte)0);

    }

    static Unsafe unsafe() {

        return unsafe;

    }

    private static int pageSize = -1;

    static int pageSize() {

        if (pageSize == -1)

            pageSize = unsafe().pageSize();

        return pageSize;

    }

    private static volatile Constructor<?> directByteBufferConstructor;

    private static void initDBBConstructor() {

        AccessController.doPrivileged(new PrivilegedAction<Void>() {

                public Void run() {

                    try {

                        Class<?> cl = Class.forName("java.nio.DirectByteBuffer");

                        Constructor<?> ctor = cl.getDeclaredConstructor(

                            new Class<?>[] { int.class,

                                             long.class,

                                             FileDescriptor.class,

                                             Runnable.class });

                        ctor.setAccessible(true);

                        directByteBufferConstructor = ctor;

                    } catch (ClassNotFoundException   |

                             NoSuchMethodException    |

                             IllegalArgumentException |

                             ClassCastException x) {

                        throw new InternalError(x);

                    }

                    return null;

                }});

    }

    static MappedByteBuffer newMappedByteBuffer(int size, long addr,

                                                FileDescriptor fd,

                                                Runnable unmapper)

    {

        MappedByteBuffer dbb;

        if (directByteBufferConstructor == null)

            initDBBConstructor();

        try {

            dbb = (MappedByteBuffer)directByteBufferConstructor.newInstance(

              new Object[] { size,

                             addr,

                             fd,

                             unmapper });

        } catch (InstantiationException |

                 IllegalAccessException |

                 InvocationTargetException e) {

            throw new InternalError(e);

        }

        return dbb;

    }

    private static volatile Constructor<?> directByteBufferRConstructor;

    private static void initDBBRConstructor() {

        AccessController.doPrivileged(new PrivilegedAction<Void>() {

                public Void run() {

                    try {

                        Class<?> cl = Class.forName("java.nio.DirectByteBufferR");

                        Constructor<?> ctor = cl.getDeclaredConstructor(

                            new Class<?>[] { int.class,

                                             long.class,

                                             FileDescriptor.class,

                                             Runnable.class });

                        ctor.setAccessible(true);

                        directByteBufferRConstructor = ctor;

                    } catch (ClassNotFoundException |

                             NoSuchMethodException |

                             IllegalArgumentException |

                             ClassCastException x) {

                        throw new InternalError(x);

                    }

                    return null;

                }});

    }

    static MappedByteBuffer newMappedByteBufferR(int size, long addr,

                                                 FileDescriptor fd,

                                                 Runnable unmapper)

    {

        MappedByteBuffer dbb;

        if (directByteBufferRConstructor == null)

            initDBBRConstructor();

        try {

            dbb = (MappedByteBuffer)directByteBufferRConstructor.newInstance(

              new Object[] { size,

                             addr,

                             fd,

                             unmapper });

        } catch (InstantiationException |

                 IllegalAccessException |

                 InvocationTargetException e) {

            throw new InternalError(e);

        }

        return dbb;

    }