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36 package java.util.concurrent.atomic;
37 import sun.misc.Unsafe;
41 * A {@code long} array in which elements may be updated atomically.
42 * See the {@link java.util.concurrent.atomic} package specification
43 * for description of the properties of atomic variables.
47 public class AtomicLongArray implements java.io.Serializable {
48 private static final long serialVersionUID = -2308431214976778248L;
50 private static final Unsafe unsafe = Unsafe.getUnsafe();
51 private static final int base = unsafe.arrayBaseOffset(long[].class);
52 private static final int shift;
53 private final long[] array;
56 int scale = unsafe.arrayIndexScale(long[].class);
57 if ((scale & (scale - 1)) != 0)
58 throw new Error("data type scale not a power of two");
59 shift = 31 - Integer.numberOfLeadingZeros(scale);
62 private long checkedByteOffset(int i) {
63 if (i < 0 || i >= array.length)
64 throw new IndexOutOfBoundsException("index " + i);
69 private static long byteOffset(int i) {
70 return ((long) i << shift) + base;
74 * Creates a new AtomicLongArray of the given length, with all
75 * elements initially zero.
77 * @param length the length of the array
79 public AtomicLongArray(int length) {
80 array = new long[length];
84 * Creates a new AtomicLongArray with the same length as, and
85 * all elements copied from, the given array.
87 * @param array the array to copy elements from
88 * @throws NullPointerException if array is null
90 public AtomicLongArray(long[] array) {
91 // Visibility guaranteed by final field guarantees
92 this.array = array.clone();
96 * Returns the length of the array.
98 * @return the length of the array
100 public final int length() {
105 * Gets the current value at position {@code i}.
108 * @return the current value
110 public final long get(int i) {
111 return getRaw(checkedByteOffset(i));
114 private long getRaw(long offset) {
115 return unsafe.getLongVolatile(array, offset);
119 * Sets the element at position {@code i} to the given value.
122 * @param newValue the new value
124 public final void set(int i, long newValue) {
125 unsafe.putLongVolatile(array, checkedByteOffset(i), newValue);
129 * Eventually sets the element at position {@code i} to the given value.
132 * @param newValue the new value
135 public final void lazySet(int i, long newValue) {
136 unsafe.putOrderedLong(array, checkedByteOffset(i), newValue);
141 * Atomically sets the element at position {@code i} to the given value
142 * and returns the old value.
145 * @param newValue the new value
146 * @return the previous value
148 public final long getAndSet(int i, long newValue) {
149 long offset = checkedByteOffset(i);
151 long current = getRaw(offset);
152 if (compareAndSetRaw(offset, current, newValue))
158 * Atomically sets the element at position {@code i} to the given
159 * updated value if the current value {@code ==} the expected value.
162 * @param expect the expected value
163 * @param update the new value
164 * @return true if successful. False return indicates that
165 * the actual value was not equal to the expected value.
167 public final boolean compareAndSet(int i, long expect, long update) {
168 return compareAndSetRaw(checkedByteOffset(i), expect, update);
171 private boolean compareAndSetRaw(long offset, long expect, long update) {
172 return unsafe.compareAndSwapLong(array, offset, expect, update);
176 * Atomically sets the element at position {@code i} to the given
177 * updated value if the current value {@code ==} the expected value.
179 * <p>May <a href="package-summary.html#Spurious">fail spuriously</a>
180 * and does not provide ordering guarantees, so is only rarely an
181 * appropriate alternative to {@code compareAndSet}.
184 * @param expect the expected value
185 * @param update the new value
186 * @return true if successful.
188 public final boolean weakCompareAndSet(int i, long expect, long update) {
189 return compareAndSet(i, expect, update);
193 * Atomically increments by one the element at index {@code i}.
196 * @return the previous value
198 public final long getAndIncrement(int i) {
199 return getAndAdd(i, 1);
203 * Atomically decrements by one the element at index {@code i}.
206 * @return the previous value
208 public final long getAndDecrement(int i) {
209 return getAndAdd(i, -1);
213 * Atomically adds the given value to the element at index {@code i}.
216 * @param delta the value to add
217 * @return the previous value
219 public final long getAndAdd(int i, long delta) {
220 long offset = checkedByteOffset(i);
222 long current = getRaw(offset);
223 if (compareAndSetRaw(offset, current, current + delta))
229 * Atomically increments by one the element at index {@code i}.
232 * @return the updated value
234 public final long incrementAndGet(int i) {
235 return addAndGet(i, 1);
239 * Atomically decrements by one the element at index {@code i}.
242 * @return the updated value
244 public final long decrementAndGet(int i) {
245 return addAndGet(i, -1);
249 * Atomically adds the given value to the element at index {@code i}.
252 * @param delta the value to add
253 * @return the updated value
255 public long addAndGet(int i, long delta) {
256 long offset = checkedByteOffset(i);
258 long current = getRaw(offset);
259 long next = current + delta;
260 if (compareAndSetRaw(offset, current, next))
266 * Returns the String representation of the current values of array.
267 * @return the String representation of the current values of array
269 public String toString() {
270 int iMax = array.length - 1;
274 StringBuilder b = new StringBuilder();
276 for (int i = 0; ; i++) {
277 b.append(getRaw(byteOffset(i)));
279 return b.append(']').toString();
280 b.append(',').append(' ');