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
26package sun.nio.fs;
27
28import jdk.internal.misc.Unsafe;
29
30/**
31 * Factory for native buffers.
32 */
33
34class 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.free();
111                buffers[i] = buffer;
112                return;
113            }
114        }
115
116        // free it
117        buffer.free();
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}
141