32 * Expert Group and released to the public domain, as explained at |
32 * Expert Group and released to the public domain, as explained at |
33 * http://creativecommons.org/publicdomain/zero/1.0/ |
33 * http://creativecommons.org/publicdomain/zero/1.0/ |
34 */ |
34 */ |
35 |
35 |
36 package java.util.concurrent.atomic; |
36 package java.util.concurrent.atomic; |
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37 |
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38 import java.lang.reflect.Array; |
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39 import java.util.Arrays; |
37 import sun.misc.Unsafe; |
40 import sun.misc.Unsafe; |
38 import java.util.*; |
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39 |
41 |
40 /** |
42 /** |
41 * An array of object references in which elements may be updated |
43 * An array of object references in which elements may be updated |
42 * atomically. See the {@link java.util.concurrent.atomic} package |
44 * atomically. See the {@link java.util.concurrent.atomic} package |
43 * specification for description of the properties of atomic |
45 * specification for description of the properties of atomic |
47 * @param <E> The base class of elements held in this array |
49 * @param <E> The base class of elements held in this array |
48 */ |
50 */ |
49 public class AtomicReferenceArray<E> implements java.io.Serializable { |
51 public class AtomicReferenceArray<E> implements java.io.Serializable { |
50 private static final long serialVersionUID = -6209656149925076980L; |
52 private static final long serialVersionUID = -6209656149925076980L; |
51 |
53 |
52 private static final Unsafe unsafe = Unsafe.getUnsafe(); |
54 private static final Unsafe unsafe; |
53 private static final int base = unsafe.arrayBaseOffset(Object[].class); |
55 private static final int base; |
54 private static final int shift; |
56 private static final int shift; |
55 private final Object[] array; |
57 private static final long arrayFieldOffset; |
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58 private final Object[] array; // must have exact type Object[] |
56 |
59 |
57 static { |
60 static { |
58 int scale = unsafe.arrayIndexScale(Object[].class); |
61 int scale; |
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62 try { |
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63 unsafe = Unsafe.getUnsafe(); |
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64 arrayFieldOffset = unsafe.objectFieldOffset |
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65 (AtomicReferenceArray.class.getDeclaredField("array")); |
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66 base = unsafe.arrayBaseOffset(Object[].class); |
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67 scale = unsafe.arrayIndexScale(Object[].class); |
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68 } catch (Exception e) { |
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69 throw new Error(e); |
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70 } |
59 if ((scale & (scale - 1)) != 0) |
71 if ((scale & (scale - 1)) != 0) |
60 throw new Error("data type scale not a power of two"); |
72 throw new Error("data type scale not a power of two"); |
61 shift = 31 - Integer.numberOfLeadingZeros(scale); |
73 shift = 31 - Integer.numberOfLeadingZeros(scale); |
62 } |
74 } |
63 |
75 |
89 * @param array the array to copy elements from |
101 * @param array the array to copy elements from |
90 * @throws NullPointerException if array is null |
102 * @throws NullPointerException if array is null |
91 */ |
103 */ |
92 public AtomicReferenceArray(E[] array) { |
104 public AtomicReferenceArray(E[] array) { |
93 // Visibility guaranteed by final field guarantees |
105 // Visibility guaranteed by final field guarantees |
94 this.array = array.clone(); |
106 this.array = Arrays.copyOf(array, array.length, Object[].class); |
95 } |
107 } |
96 |
108 |
97 /** |
109 /** |
98 * Returns the length of the array. |
110 * Returns the length of the array. |
99 * |
111 * |
148 * @return the previous value |
160 * @return the previous value |
149 */ |
161 */ |
150 public final E getAndSet(int i, E newValue) { |
162 public final E getAndSet(int i, E newValue) { |
151 long offset = checkedByteOffset(i); |
163 long offset = checkedByteOffset(i); |
152 while (true) { |
164 while (true) { |
153 E current = (E) getRaw(offset); |
165 E current = getRaw(offset); |
154 if (compareAndSetRaw(offset, current, newValue)) |
166 if (compareAndSetRaw(offset, current, newValue)) |
155 return current; |
167 return current; |
156 } |
168 } |
157 } |
169 } |
158 |
170 |
194 /** |
206 /** |
195 * Returns the String representation of the current values of array. |
207 * Returns the String representation of the current values of array. |
196 * @return the String representation of the current values of array |
208 * @return the String representation of the current values of array |
197 */ |
209 */ |
198 public String toString() { |
210 public String toString() { |
199 int iMax = array.length - 1; |
211 int iMax = array.length - 1; |
200 if (iMax == -1) |
212 if (iMax == -1) |
201 return "[]"; |
213 return "[]"; |
202 |
214 |
203 StringBuilder b = new StringBuilder(); |
215 StringBuilder b = new StringBuilder(); |
204 b.append('['); |
216 b.append('['); |
208 return b.append(']').toString(); |
220 return b.append(']').toString(); |
209 b.append(',').append(' '); |
221 b.append(',').append(' '); |
210 } |
222 } |
211 } |
223 } |
212 |
224 |
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225 /** |
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226 * Reconstitutes the instance from a stream (that is, deserializes it). |
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227 * @param s the stream |
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228 */ |
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229 private void readObject(java.io.ObjectInputStream s) |
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230 throws java.io.IOException, ClassNotFoundException { |
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231 // Note: This must be changed if any additional fields are defined |
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232 Object a = s.readFields().get("array", null); |
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233 if (a == null || !a.getClass().isArray()) |
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234 throw new java.io.InvalidObjectException("Not array type"); |
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235 if (a.getClass() != Object[].class) |
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236 a = Arrays.copyOf((Object[])a, Array.getLength(a), Object[].class); |
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237 unsafe.putObjectVolatile(this, arrayFieldOffset, a); |
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238 } |
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239 |
213 } |
240 } |