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4  *
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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).
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24  */
25 
26 package sun.nio.fs;
27 
28 import sun.misc.Unsafe;
29 
30 /**
31  * Factory for native buffers.
32  */
33 
34 class NativeBuffers {
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      */
allocNativeBuffer(int size)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      */
getNativeBufferFromCache(int size)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      */
getNativeBuffer(int size)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      */
releaseNativeBuffer(NativeBuffer buffer)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      */
copyCStringToNativeBuffer(byte[] cstr, NativeBuffer buffer)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      */
asNativeBuffer(byte[] cstr)135     static NativeBuffer asNativeBuffer(byte[] cstr) {
136         NativeBuffer buffer = getNativeBuffer(cstr.length+1);
137         copyCStringToNativeBuffer(cstr, buffer);
138         return buffer;
139     }
140 }
141