rev 12972 : 8140606: Update library code to use internal Unsafe
Reviewed-by: duke

   1 /*
   2  * Copyright (c) 2008, 2009, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package sun.nio.fs;
  27 
  28 import jdk.internal.misc.Unsafe;
  29 
  30 /**
  31  * Factory for native buffers.
  32  */
  33 
  34 class NativeBuffers {
  35     private NativeBuffers() { }
  36 
  37     private static final Unsafe unsafe = Unsafe.getUnsafe();
  38 
  39     private static final int TEMP_BUF_POOL_SIZE = 3;
  40     private static ThreadLocal<NativeBuffer[]> threadLocal =
  41         new ThreadLocal<NativeBuffer[]>();
  42 
  43     /**
  44      * Allocates a native buffer, of at least the given size, from the heap.
  45      */
  46     static NativeBuffer allocNativeBuffer(int size) {
  47         // Make a new one of at least 2k
  48         if (size < 2048) size = 2048;
  49         return new NativeBuffer(size);
  50     }
  51 
  52     /**
  53      * Returns a native buffer, of at least the given size, from the thread
  54      * local cache.
  55      */
  56     static NativeBuffer getNativeBufferFromCache(int size) {
  57         // return from cache if possible
  58         NativeBuffer[] buffers = threadLocal.get();
  59         if (buffers != null) {
  60             for (int i=0; i<TEMP_BUF_POOL_SIZE; i++) {
  61                 NativeBuffer buffer = buffers[i];
  62                 if (buffer != null && buffer.size() >= size) {
  63                     buffers[i] = null;
  64                     return buffer;
  65                 }
  66             }
  67         }
  68         return null;
  69     }
  70 
  71     /**
  72      * Returns a native buffer, of at least the given size. The native buffer
  73      * is taken from the thread local cache if possible; otherwise it is
  74      * allocated from the heap.
  75      */
  76     static NativeBuffer getNativeBuffer(int size) {
  77         NativeBuffer buffer = getNativeBufferFromCache(size);
  78         if (buffer != null) {
  79             buffer.setOwner(null);
  80             return buffer;
  81         } else {
  82             return allocNativeBuffer(size);
  83         }
  84     }
  85 
  86     /**
  87      * Releases the given buffer. If there is space in the thread local cache
  88      * then the buffer goes into the cache; otherwise the memory is deallocated.
  89      */
  90     static void releaseNativeBuffer(NativeBuffer buffer) {
  91         // create cache if it doesn't exist
  92         NativeBuffer[] buffers = threadLocal.get();
  93         if (buffers == null) {
  94             buffers = new NativeBuffer[TEMP_BUF_POOL_SIZE];
  95             buffers[0] = buffer;
  96             threadLocal.set(buffers);
  97             return;
  98         }
  99         // Put it in an empty slot if such exists
 100         for (int i=0; i<TEMP_BUF_POOL_SIZE; i++) {
 101             if (buffers[i] == null) {
 102                 buffers[i] = buffer;
 103                 return;
 104             }
 105         }
 106         // Otherwise replace a smaller one in the cache if such exists
 107         for (int i=0; i<TEMP_BUF_POOL_SIZE; i++) {
 108             NativeBuffer existing = buffers[i];
 109             if (existing.size() < buffer.size()) {
 110                 existing.cleaner().clean();
 111                 buffers[i] = buffer;
 112                 return;
 113             }
 114         }
 115 
 116         // free it
 117         buffer.cleaner().clean();
 118     }
 119 
 120     /**
 121      * Copies a byte array and zero terminator into a given native buffer.
 122      */
 123     static void copyCStringToNativeBuffer(byte[] cstr, NativeBuffer buffer) {
 124         long offset = Unsafe.ARRAY_BYTE_BASE_OFFSET;
 125         long len = cstr.length;
 126         assert buffer.size() >= (len + 1);
 127         unsafe.copyMemory(cstr, offset, null, buffer.address(), len);
 128         unsafe.putByte(buffer.address() + len, (byte)0);
 129     }
 130 
 131     /**
 132      * Copies a byte array and zero terminator into a native buffer, returning
 133      * the buffer.
 134      */
 135     static NativeBuffer asNativeBuffer(byte[] cstr) {
 136         NativeBuffer buffer = getNativeBuffer(cstr.length+1);
 137         copyCStringToNativeBuffer(cstr, buffer);
 138         return buffer;
 139     }
 140 }
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