AtomicLongArray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。 boolean weakCompareAndSet(int i, long expect, long update)
AtomicLongArray源码分析(基于JDK1.7.0_40)
AtomicLongArray的完整源码
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* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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/*
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* 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 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">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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时间： 2024-10-31 12:48:17