Java多线程：“JUC原子类”03之AtomicLongArray原子类2014-06-02 cnblogs skywang12345AtomicLongArray介绍和函数列表在"Java多线程系列--“JUC原子类”02之 AtomicLong原子类"中介绍过， AtomicLong是作用是对长整形进行原子操作。而AtomicLongArray的作用则是对"长整形数组" 进行原子操作。AtomicLongArray函数列表
// 创建给定长度的新 AtomicLongArray。AtomicLongArray（int length）// 创建与给定数组具有相同长度的新 AtomicLongArray，并从给定数组复制其所有元素。AtomicLongArray（long[] array）// 以原子方式将给定值添加到索引 i 的元素。long addAndGet（int i, long delta）// 如果当前值 == 预期值，则以原子方式将该值设置为给定的更新值。boolean compareAndSet（int i, long expect, long update）// 以原子方式将索引 i 的元素减1。long decrementAndGet（int i）// 获取位置 i 的当前值。long get（int i）// 以原子方式将给定值与索引 i 的元素相加。long getAndAdd（int i, long delta）// 以原子方式将索引 i 的元素减 1。long getAndDecrement（int i）// 以原子方式将索引 i 的元素加 1。long getAndIncrement（int i）// 以原子方式将位置 i 的元素设置为给定值，并返回旧值。long getAndSet（int i, long newValue）// 以原子方式将索引 i 的元素加1。long incrementAndGet（int i）// 最终将位置 i 的元素设置为给定值。void lazySet（int i, long newValue）// 返回该数组的长度。int length（）// 将位置 i 的元素设置为给定值。void set（int i, long newValue）// 返回数组当前值的字符串表示形式。String toString（）// 如果当前值 == 预期值，则以原子方式将该值设置为给定的更新值。booleanweakCompareAndSet（int i, long expect, long update）
AtomicLongArray源码分析（基于JDK1.7.0_40）AtomicLongArray的完整源码
/* * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. * * * * * * * * * * * * * * * * * * * * *//* * * * * * * 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;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 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 guaranteesthis.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">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（" "）;}}} 
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