JDK提供的原子类原理与使用
2024-10-20 05:44:22
原子更新基本类型
原子更新数组
原子更新抽象类型
原子更新字段
原子更新基本类型:
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);//给下标为2的元素加1
a.getAndAdd(2, 10);//获取下标为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();
}
}
运行结果:
Thread-0 0
Thread-1 1
Thread-2 2
Thread-0 3
Thread-1 4
Thread-2 5
...
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<>(); //对user的set和get执行原子操作
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() {
@Override
public void run() {
System.out.println(Thread.currentThread().getName()+" "+sequence.getNext());
try {
Thread.sleep(100);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}).start();
}
}
运行结果:
0
1
2
Thread-0 0
对CAS的源码理解:--初步理解
在AtomicInteger中有这样一段源码:
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的缩写。如果prev和next不相等,则返回true。否则,返回false。最终是通过unsafe来实现的。
以上代码表示,如果compareAndSet返回true,则while条件为false,退出循环,返回prev值。如果compareAndSet返回false,则while为true,继续执行循环体,重新获取prev的值,重新获取更新值,直到返回的compareAndSet值为true。
演示源码大致步骤如下:
Object prev = get(); //
next = prev + 1;
boolean flag = cas(prev, next);
if (flag) {
return prev;
}else {
go to 1
}
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