AtomicLongArray介紹和函數列表
AtomicLongArray函數列表
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// 創建給定長度的新 AtomicLongArray。AtomicLongArray(int length)// 創建與給定數組具有相同長度的新 AtomicLongArray，并從給定數組復制其所有元素。AtomicLongArray(long[] array)// 以原子方式將給定值添加到索引 i 的元素。long addAndGet(int i, long delta)// 如果當前值 == 預期值，則以原子方式將該值設置為給定的更新值。boolean compareAndSet(int i, long expect, long update)// 以原子方式將索引 i 的元素減1。long decrementAndGet(int i)// 獲取位置 i 的當前值。long get(int i)// 以原子方式將給定值與索引 i 的元素相加。long getAndAdd(int i, long delta)// 以原子方式將索引 i 的元素減 1。long getAndDecrement(int i)// 以原子方式將索引 i 的元素加 1。long getAndIncrement(int i)// 以原子方式將位置 i 的元素設置為給定值，并返回舊值。long getAndSet(int i, long newValue)// 以原子方式將索引 i 的元素加1。long incrementAndGet(int i)// 最終將位置 i 的元素設置為給定值。void lazySet(int i, long newValue)// 返回該數組的長度。int length()// 將位置 i 的元素設置為給定值。void set(int i, long newValue)// 返回數組當前值的字符串表示形式。String toString()// 如果當前值 == 預期值，則以原子方式將該值設置為給定的更新值。boolean weakCompareAndSet(int i, long expect, long update) |
AtomicLongArray源碼分析(基于JDK1.7.0_40)
AtomicLongArray的完整源碼
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/* * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. * * * * * * * * * * * * * * * * * * * * *//* * * * * * * Written by Doug Lea with assistance from members of JCP JSR- * Expert Group and released to the public domain, as explained at * http://creativecommons.org/publicdomain/zero/./ */package java.util.concurrent.atomic;import sun.misc.Unsafe;import java.util.*;/** * 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 . * @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 - )) != ) throw new Error("data type scale not a power of two"); shift = - Integer.numberOfLeadingZeros(scale); } private long checkedByteOffset(int i) { if (i < || 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>May <a href="package-summary.html#Spurious" rel="external nofollow" >fail spuriously</a> * and does not provide ordering guarantees, 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(' '); } }} |
AtomicLongArray的代碼很簡單，下面僅以incrementAndGet()為例，對AtomicLong的原理進行說明。
incrementAndGet()源碼如下：
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public final long incrementAndGet(int i) { return addAndGet(i, 1);} |
說明：incrementAndGet()的作用是以原子方式將long數組的索引 i 的元素加1，并返回加1之后的值。
addAndGet()源碼如下：
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public long addAndGet(int i, long delta) { // 檢查數組是否越界 long offset = checkedByteOffset(i); while (true) { // 獲取long型數組的索引 offset 的原始值 long current = getRaw(offset); // 修改long型值 long next = current + delta; // 通過CAS更新long型數組的索引 offset的值。 if (compareAndSetRaw(offset, current, next)) return next; }} |
說明：addAndGet()首先檢查數組是否越界。如果沒有越界的話，則先獲取數組索引i的值；然后通過CAS函數更新i的值。
getRaw()源碼如下：
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private long getRaw(long offset) { return unsafe.getLongVolatile(array, offset);} |
說明：unsafe是通過Unsafe.getUnsafe()返回的一個Unsafe對象。通過Unsafe的CAS函數對long型數組的元素進行原子操作。如compareAndSetRaw()就是調用Unsafe的CAS函數，它的源碼如下：
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private boolean compareAndSetRaw(long offset, long expect, long update) { return unsafe.compareAndSwapLong(array, offset, expect, update);} |
AtomicLongArray示例
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// LongArrayTest.java的源碼import java.util.concurrent.atomic.AtomicLongArray;public class LongArrayTest { public static void main(String[] args){ // 新建AtomicLongArray對象 long[] arrLong = new long[] {10, 20, 30, 40, 50}; AtomicLongArray ala = new AtomicLongArray(arrLong); ala.set(0, 100); for (int i=0, len=ala.length(); i<len; i++) System.out.printf("get(%d) : %s\n", i, ala.get(i)); System.out.printf("%20s : %s\n", "getAndDecrement(0)", ala.getAndDecrement(0)); System.out.printf("%20s : %s\n", "decrementAndGet(1)", ala.decrementAndGet(1)); System.out.printf("%20s : %s\n", "getAndIncrement(2)", ala.getAndIncrement(2)); System.out.printf("%20s : %s\n", "incrementAndGet(3)", ala.incrementAndGet(3)); System.out.printf("%20s : %s\n", "addAndGet(100)", ala.addAndGet(0, 100)); System.out.printf("%20s : %s\n", "getAndAdd(100)", ala.getAndAdd(1, 100)); System.out.printf("%20s : %s\n", "compareAndSet()", ala.compareAndSet(2, 31, 1000)); System.out.printf("%20s : %s\n", "get(2)", ala.get(2)); }} |
運行結果：
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get(0) : 100get(1) : 20get(2) : 30get(3) : 40get(4) : 50 getAndDecrement(0) : 100 decrementAndGet(1) : 19 getAndIncrement(2) : 30 incrementAndGet(3) : 41 addAndGet(100) : 199 getAndAdd(100) : 19 compareAndSet() : true get(2) : 1000 |
以上所述是小編給大家介紹的Java concurrency之AtomicLongArray原子類，希望對大家有所幫助，如果大家有任何疑問請給我留言，小編會及時回復大家的。在此也非常感謝大家對服務器之家網站的支持！
