concurrent/atomic/AtomicLongArray.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

package java.util.concurrent.atomic;
import sun.misc.Unsafe;

/**
 * A {@code long} array in which elements may be updated atomically.
 * See the {@link java.util.concurrent.atomic} package specification
 * for description of the properties of atomic variables.
 * @since 1.5
 * @author Doug Lea
 */
public class AtomicLongArray implements java.io.Serializable {
    private static final long serialVersionUID = -2308431214976778248L;

    private static final Unsafe unsafe = Unsafe.getUnsafe();
    private static final int base = unsafe.arrayBaseOffset(long[].class);
    private static final int shift;
    private final long[] array;

    static {
        int scale = unsafe.arrayIndexScale(long[].class);
        if ((scale & (scale - 1)) != 0)
            throw new Error("data type scale not a power of two");
        shift = 31 - Integer.numberOfLeadingZeros(scale);
    }

    private long checkedByteOffset(int i) {
        if (i < 0 || i >= array.length)
            throw new IndexOutOfBoundsException("index " + i);

        return byteOffset(i);
    }

    private static long byteOffset(int i) {
        return ((long) i << shift) + base;
    }

    /**
     * Creates a new AtomicLongArray of the given length, with all
     * elements initially zero.
     *
     * @param length the length of the array
     */
    public AtomicLongArray(int length) {
        array = new long[length];
    }

    /**
     * Creates a new AtomicLongArray with the same length as, and
     * all elements copied from, the given array.
     *
     * @param array the array to copy elements from
     * @throws NullPointerException if array is null
     */
    public AtomicLongArray(long[] array) {
        // Visibility guaranteed by final field guarantees
        this.array = array.clone();
    }

    /**
     * Returns the length of the array.
     *
     * @return the length of the array
     */
    public final int length() {
        return array.length;
    }

    /**
     * Gets the current value at position {@code i}.
     *
     * @param i the index
     * @return the current value
     */
    public final long get(int i) {
        return getRaw(checkedByteOffset(i));
    }

    private long getRaw(long offset) {
        return unsafe.getLongVolatile(array, offset);
    }

    /**
     * Sets the element at position {@code i} to the given value.
     *
     * @param i the index
     * @param newValue the new value
     */
    public final void set(int i, long newValue) {
        unsafe.putLongVolatile(array, checkedByteOffset(i), newValue);
    }

    /**
     * Eventually sets the element at position {@code i} to the given value.
     *
     * @param i the index
     * @param newValue the new value
     * @since 1.6
     */
    public final void lazySet(int i, long newValue) {
        unsafe.putOrderedLong(array, checkedByteOffset(i), newValue);
    }

    /**
     * Atomically sets the element at position {@code i} to the given value
     * and returns the old value.
     *
     * @param i the index
     * @param newValue the new value
     * @return the previous value
     */
    public final long getAndSet(int i, long newValue) {
        long offset = checkedByteOffset(i);
        while (true) {
            long current = getRaw(offset);
            if (compareAndSetRaw(offset, current, newValue))
                return current;
        }
    }

    /**
     * Atomically sets the element at position {@code i} to the given
     * updated value if the current value {@code ==} the expected value.
     *
     * @param i the index
     * @param expect the expected value
     * @param update the new value
     * @return true if successful. False return indicates that
     * the actual value was not equal to the expected value.
     */
    public final boolean compareAndSet(int i, long expect, long update) {
        return compareAndSetRaw(checkedByteOffset(i), expect, update);
    }

    private boolean compareAndSetRaw(long offset, long expect, long update) {
        return unsafe.compareAndSwapLong(array, offset, expect, update);
    }

    /**
     * Atomically sets the element at position {@code i} to the given
     * updated value if the current value {@code ==} the expected value.
     *
     * <p><a href="package-summary.html#weakCompareAndSet">May fail
     * spuriously and does not provide ordering guarantees</a>, so is
     * only rarely an appropriate alternative to {@code compareAndSet}.
     *
     * @param i the index
     * @param expect the expected value
     * @param update the new value
     * @return true if successful
     */
    public final boolean weakCompareAndSet(int i, long expect, long update) {
        return compareAndSet(i, expect, update);
    }

    /**
     * Atomically increments by one the element at index {@code i}.
     *
     * @param i the index
     * @return the previous value
     */
    public final long getAndIncrement(int i) {
        return getAndAdd(i, 1);
    }

    /**
     * Atomically decrements by one the element at index {@code i}.
     *
     * @param i the index
     * @return the previous value
     */
    public final long getAndDecrement(int i) {
        return getAndAdd(i, -1);
    }

    /**
     * Atomically adds the given value to the element at index {@code i}.
     *
     * @param i the index
     * @param delta the value to add
     * @return the previous value
     */
    public final long getAndAdd(int i, long delta) {
        long offset = checkedByteOffset(i);
        while (true) {
            long current = getRaw(offset);
            if (compareAndSetRaw(offset, current, current + delta))
                return current;
        }
    }

    /**
     * Atomically increments by one the element at index {@code i}.
     *
     * @param i the index
     * @return the updated value
     */
    public final long incrementAndGet(int i) {
        return addAndGet(i, 1);
    }

    /**
     * Atomically decrements by one the element at index {@code i}.
     *
     * @param i the index
     * @return the updated value
     */
    public final long decrementAndGet(int i) {
        return addAndGet(i, -1);
    }

    /**
     * Atomically adds the given value to the element at index {@code i}.
     *
     * @param i the index
     * @param delta the value to add
     * @return the updated value
     */
    public long addAndGet(int i, long delta) {
        long offset = checkedByteOffset(i);
        while (true) {
            long current = getRaw(offset);
            long next = current + delta;
            if (compareAndSetRaw(offset, current, next))
                return next;
        }
    }

    /**
     * Returns the String representation of the current values of array.
     * @return the String representation of the current values of array
     */
    public String toString() {
        int iMax = array.length - 1;
        if (iMax == -1)
            return "[]";

        StringBuilder b = new StringBuilder();
        b.append('[');
        for (int i = 0; ; i++) {
            b.append(getRaw(byteOffset(i)));
            if (i == iMax)
                return b.append(']').toString();
            b.append(',').append(' ');
        }
    }

}
Revision:	1.3
Committed:	Mon Mar 4 16:09:25 2013 UTC (11 years, 3 months ago) by jsr166
Branch:	MAIN
Changes since 1.2:	+3 -3 lines
Log Message:	improve javadoc anchored text
#	Content
1	/*
2	* Written by Doug Lea with assistance from members of JCP JSR-166
3	* Expert Group and released to the public domain, as explained at
4	* http://creativecommons.org/publicdomain/zero/1.0/
5	*/
6
7	package java.util.concurrent.atomic;
8	import sun.misc.Unsafe;
9
10	/**
11	* A {@code long} array in which elements may be updated atomically.
12	* See the {@link java.util.concurrent.atomic} package specification
13	* for description of the properties of atomic variables.
14	* @since 1.5
15	* @author Doug Lea
16	*/
17	public class AtomicLongArray implements java.io.Serializable {
18	private static final long serialVersionUID = -2308431214976778248L;
19
20	private static final Unsafe unsafe = Unsafe.getUnsafe();
21	private static final int base = unsafe.arrayBaseOffset(long[].class);
22	private static final int shift;
23	private final long[] array;
24
25	static {
26	int scale = unsafe.arrayIndexScale(long[].class);
27	if ((scale & (scale - 1)) != 0)
28	throw new Error("data type scale not a power of two");
29	shift = 31 - Integer.numberOfLeadingZeros(scale);
30	}
31
32	private long checkedByteOffset(int i) {
33	if (i < 0 \|\| i >= array.length)
34	throw new IndexOutOfBoundsException("index " + i);
35
36	return byteOffset(i);
37	}
38
39	private static long byteOffset(int i) {
40	return ((long) i << shift) + base;
41	}
42
43	/**
44	* Creates a new AtomicLongArray of the given length, with all
45	* elements initially zero.
46	*
47	* @param length the length of the array
48	*/
49	public AtomicLongArray(int length) {
50	array = new long[length];
51	}
52
53	/**
54	* Creates a new AtomicLongArray with the same length as, and
55	* all elements copied from, the given array.
56	*
57	* @param array the array to copy elements from
58	* @throws NullPointerException if array is null
59	*/
60	public AtomicLongArray(long[] array) {
61	// Visibility guaranteed by final field guarantees
62	this.array = array.clone();
63	}
64
65	/**
66	* Returns the length of the array.
67	*
68	* @return the length of the array
69	*/
70	public final int length() {
71	return array.length;
72	}
73
74	/**
75	* Gets the current value at position {@code i}.
76	*
77	* @param i the index
78	* @return the current value
79	*/
80	public final long get(int i) {
81	return getRaw(checkedByteOffset(i));
82	}
83
84	private long getRaw(long offset) {
85	return unsafe.getLongVolatile(array, offset);
86	}
87
88	/**
89	* Sets the element at position {@code i} to the given value.
90	*
91	* @param i the index
92	* @param newValue the new value
93	*/
94	public final void set(int i, long newValue) {
95	unsafe.putLongVolatile(array, checkedByteOffset(i), newValue);
96	}
97
98	/**
99	* Eventually sets the element at position {@code i} to the given value.
100	*
101	* @param i the index
102	* @param newValue the new value
103	* @since 1.6
104	*/
105	public final void lazySet(int i, long newValue) {
106	unsafe.putOrderedLong(array, checkedByteOffset(i), newValue);
107	}
108
109	/**
110	* Atomically sets the element at position {@code i} to the given value
111	* and returns the old value.
112	*
113	* @param i the index
114	* @param newValue the new value
115	* @return the previous value
116	*/
117	public final long getAndSet(int i, long newValue) {
118	long offset = checkedByteOffset(i);
119	while (true) {
120	long current = getRaw(offset);
121	if (compareAndSetRaw(offset, current, newValue))
122	return current;
123	}
124	}
125
126	/**
127	* Atomically sets the element at position {@code i} to the given
128	* updated value if the current value {@code ==} the expected value.
129	*
130	* @param i the index
131	* @param expect the expected value
132	* @param update the new value
133	* @return true if successful. False return indicates that
134	* the actual value was not equal to the expected value.
135	*/
136	public final boolean compareAndSet(int i, long expect, long update) {
137	return compareAndSetRaw(checkedByteOffset(i), expect, update);
138	}
139
140	private boolean compareAndSetRaw(long offset, long expect, long update) {
141	return unsafe.compareAndSwapLong(array, offset, expect, update);
142	}
143
144	/**
145	* Atomically sets the element at position {@code i} to the given
146	* updated value if the current value {@code ==} the expected value.
147	*
148	* <p><a href="package-summary.html#weakCompareAndSet">May fail
149	* spuriously and does not provide ordering guarantees</a>, so is
150	* only rarely an appropriate alternative to {@code compareAndSet}.
151	*
152	* @param i the index
153	* @param expect the expected value
154	* @param update the new value
155	* @return true if successful
156	*/
157	public final boolean weakCompareAndSet(int i, long expect, long update) {
158	return compareAndSet(i, expect, update);
159	}
160
161	/**
162	* Atomically increments by one the element at index {@code i}.
163	*
164	* @param i the index
165	* @return the previous value
166	*/
167	public final long getAndIncrement(int i) {
168	return getAndAdd(i, 1);
169	}
170
171	/**
172	* Atomically decrements by one the element at index {@code i}.
173	*
174	* @param i the index
175	* @return the previous value
176	*/
177	public final long getAndDecrement(int i) {
178	return getAndAdd(i, -1);
179	}
180
181	/**
182	* Atomically adds the given value to the element at index {@code i}.
183	*
184	* @param i the index
185	* @param delta the value to add
186	* @return the previous value
187	*/
188	public final long getAndAdd(int i, long delta) {
189	long offset = checkedByteOffset(i);
190	while (true) {
191	long current = getRaw(offset);
192	if (compareAndSetRaw(offset, current, current + delta))
193	return current;
194	}
195	}
196
197	/**
198	* Atomically increments by one the element at index {@code i}.
199	*
200	* @param i the index
201	* @return the updated value
202	*/
203	public final long incrementAndGet(int i) {
204	return addAndGet(i, 1);
205	}
206
207	/**
208	* Atomically decrements by one the element at index {@code i}.
209	*
210	* @param i the index
211	* @return the updated value
212	*/
213	public final long decrementAndGet(int i) {
214	return addAndGet(i, -1);
215	}
216
217	/**
218	* Atomically adds the given value to the element at index {@code i}.
219	*
220	* @param i the index
221	* @param delta the value to add
222	* @return the updated value
223	*/
224	public long addAndGet(int i, long delta) {
225	long offset = checkedByteOffset(i);
226	while (true) {
227	long current = getRaw(offset);
228	long next = current + delta;
229	if (compareAndSetRaw(offset, current, next))
230	return next;
231	}
232	}
233
234	/**
235	* Returns the String representation of the current values of array.
236	* @return the String representation of the current values of array
237	*/
238	public String toString() {
239	int iMax = array.length - 1;
240	if (iMax == -1)
241	return "[]";
242
243	StringBuilder b = new StringBuilder();
244	b.append('[');
245	for (int i = 0; ; i++) {
246	b.append(getRaw(byteOffset(i)));
247	if (i == iMax)
248	return b.append(']').toString();
249	b.append(',').append(' ');
250	}
251	}
252
253	}