Java concurrency之AtomicLongArray原子类_动力节点Java学院整理
AtomicLongArray介绍和函数列表 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。 boolean weakCompareAndSet(int i,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- * 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,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 update) { return compareAndSetRaw(checkedByteOffset(i),expect,update); } private boolean compareAndSetRaw(long offset,long update) { return unsafe.compareAndSwapLong(array,offset,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 update) { return compareAndSet(i,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 + 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,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的代码很简单,下面仅以incrementAndGet()为例,对AtomicLong的原理进行说明。 incrementAndGet()源码如下: public final long incrementAndGet(int i) { return addAndGet(i,1); } 说明:incrementAndGet()的作用是以原子方式将long数组的索引 i 的元素加1,并返回加1之后的值。 addAndGet()源码如下: public long addAndGet(int i,long delta) { // 检查数组是否越界 long offset = checkedByteOffset(i); while (true) { // 获取long型数组的索引 offset 的原始值 long current = getRaw(offset); // 修改long型值 long next = current + delta; // 通过CAS更新long型数组的索引 offset的值。 if (compareAndSetRaw(offset,next)) return next; } } 说明:addAndGet()首先检查数组是否越界。如果没有越界的话,则先获取数组索引i的值;然后通过CAS函数更新i的值。 getRaw()源码如下: private long getRaw(long offset) { return unsafe.getLongVolatile(array,offset); } 说明:unsafe是通过Unsafe.getUnsafe()返回的一个Unsafe对象。通过Unsafe的CAS函数对long型数组的元素进行原子操作。如compareAndSetRaw()就是调用Unsafe的CAS函数,它的源码如下: private boolean compareAndSetRaw(long offset,long update) { return unsafe.compareAndSwapLong(array,update); } AtomicLongArray示例 // LongArrayTest.java的源码 import java.util.concurrent.atomic.AtomicLongArray; public class LongArrayTest { public static void main(String[] args){ // 新建AtomicLongArray对象 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) : %sn",i,ala.get(i)); System.out.printf("%20s : %sn","getAndDecrement(0)",ala.getAndDecrement(0)); System.out.printf("%20s : %sn","decrementAndGet(1)",ala.decrementAndGet(1)); System.out.printf("%20s : %sn","getAndIncrement(2)",ala.getAndIncrement(2)); System.out.printf("%20s : %sn","incrementAndGet(3)",ala.incrementAndGet(3)); System.out.printf("%20s : %sn","addAndGet(100)",ala.addAndGet(0,100)); System.out.printf("%20s : %sn","getAndAdd(100)",ala.getAndAdd(1,"compareAndSet()",ala.compareAndSet(2,31,1000)); System.out.printf("%20s : %sn","get(2)",ala.get(2)); } } 运行结果: get(0) : 100 get(1) : 20 get(2) : 30 get(3) : 40 get(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 以上所述是小编给大家介绍的Java concurrency之AtomicLongArray原子类,希望对大家有所帮助,如果大家有任何疑问请给我留言,小编会及时回复大家的。在此也非常感谢大家对编程小技巧网站的支持! 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