原子更新基本類型

原子更新數(shù)組

原子更新抽象類型

原子更新字段

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原子更新基本類型：

package com.roocon.thread.t8;

import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicIntegerArray;

public class Sequence {
private AtomicInteger value = new AtomicInteger(0);
private int [] s = {2,1,4,6};
AtomicIntegerArray a = new AtomicIntegerArray(s);

public int getNext(){
a.getAndIncrement(2);//給下標(biāo)為2的元素加1
a.getAndAdd(2, 10);//獲取下標(biāo)為2的元素，并且加10
for (int i=0; i < a.length(); i++){
System.out.println(a.get(i));
}
return value.getAndIncrement();
}

public static void main(String[] args) {
Sequence sequence = new Sequence();
new Thread(new Runnable() {
@Override
public void run() {
while (true){
System.out.println(Thread.currentThread().getName()+" "+sequence.getNext());
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}).start();
new Thread(new Runnable() {
@Override
public void run() {
while (true){
System.out.println(Thread.currentThread().getName()+" "+sequence.getNext());
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}).start();
new Thread(new Runnable() {
@Override
public void run() {
while (true){
System.out.println(Thread.currentThread().getName()+" "+sequence.getNext());
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}).start();
}
}

運行結(jié)果：

Thread-0 0 Thread-1 1 Thread-2 2 Thread-0 3 Thread-1 4 Thread-2 5 ...

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package com.roocon.thread.t8;import java.util.concurrent.atomic.AtomicInteger; import java.util.concurrent.atomic.AtomicIntegerArray; import java.util.concurrent.atomic.AtomicIntegerFieldUpdater; import java.util.concurrent.atomic.AtomicReference;public class Sequence {private AtomicInteger value = new AtomicInteger(0);AtomicReference<User> user = new AtomicReference<>(); //對user的set和get執(zhí)行原子操作AtomicIntegerFieldUpdater<User> old = AtomicIntegerFieldUpdater.newUpdater(User.class, "old");public int getNext(){User user = new User();System.out.println(old.getAndIncrement(user));System.out.println(old.getAndIncrement(user));System.out.println(old.getAndIncrement(user));return value.getAndIncrement();}public static void main(String[] args) {Sequence sequence = new Sequence();new Thread(new Runnable() {@Overridepublic void run() {System.out.println(Thread.currentThread().getName()+" "+sequence.getNext());try {Thread.sleep(100);} catch (InterruptedException e) {e.printStackTrace();}}}).start();} }

運行結(jié)果：

0 1 2 Thread-0 0

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對CAS的源碼理解：--初步理解

在AtomicInteger中有這樣一段源碼：

public final int getAndUpdate(IntUnaryOperator updateFunction) {int prev, next;do {prev = get();next = updateFunction.applyAsInt(prev);} while (!compareAndSet(prev, next));return prev;}

public final boolean compareAndSet(int expect, int update) {
return unsafe.compareAndSwapInt(this, valueOffset, expect, update);
} ?

其中，compareAndSwap就是CAS的縮寫。如果prev和next不相等，則返回true。否則，返回false。最終是通過unsafe來實現(xiàn)的。

以上代碼表示，如果compareAndSet返回true，則while條件為false，退出循環(huán)，返回prev值。如果compareAndSet返回false，則while為true，繼續(xù)執(zhí)行循環(huán)體，重新獲取prev的值，重新獲取更新值，直到返回的compareAndSet值為true。

演示源碼大致步驟如下：

Object prev = get(); //1next = prev + 1;boolean flag = cas(prev, next);if (flag) {return prev;}else {go to 1}

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轉(zhuǎn)載于:https://www.cnblogs.com/sunnyDream/p/8137588.html

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