Java并发编程-36-原子数组

一、同步机制存在的问题

1、死锁
2、即使只有一个线程访问这个对象，仍然需要执行必须的代码来获取和释放锁

二、Compare-and-Swap-Operation

1、取得变量值，即变量的旧值

2、在一个临时变量中修改变量值，即变量的新值

3、如果上面获得的变量旧值与当前变量值相等，就用新值替换旧值。如果已有其他线程修改了这个变量的值，上面获得的变量的旧值就可能与当前变量值不同

三、原子数组

package concurrencycollection;

import java.util.concurrent.atomic.AtomicIntegerArray;

public class Incrementer implements Runnable {

private AtomicIntegerArray atomicIntegerArray;

public Incrementer(AtomicIntegerArray atomicIntegerArray) {
this.atomicIntegerArray = atomicIntegerArray;
}

@Override
public void run() {
// TODO Auto-generated method stub
for (int i = 0; i < atomicIntegerArray.length(); i++) {
atomicIntegerArray.getAndIncrement(i);
}
}
}

package concurrencycollection;

import java.util.concurrent.atomic.AtomicIntegerArray;

public class Decrementer implements Runnable {
private AtomicIntegerArray atomicIntegerArray;

public Decrementer(AtomicIntegerArray atomicIntegerArray) {
this.atomicIntegerArray = atomicIntegerArray;
}

@Override
public void run() {
// TODO Auto-generated method stub
for (int i = 0; i < atomicIntegerArray.length(); i++) {
atomicIntegerArray.getAndDecrement(i);
}
}
}

package concurrencycollection;

import java.util.concurrent.atomic.AtomicIntegerArray;

public class Main {

public static void main(String[] args) {
// TODO Auto-generated method stub
AtomicIntegerArray atomicIntegerArray = new AtomicIntegerArray(1000);
final int THREADS = 100;
Incrementer incrementer = new Incrementer(atomicIntegerArray);
Decrementer decrementer = new Decrementer(atomicIntegerArray);

Thread[] threadsIncrementer = new Thread[THREADS];
Thread[] threadsDecrementer = new Thread[THREADS];

for (int i = 0; i < THREADS; i++) {
threadsIncrementer[i] = new Thread(incrementer);
threadsDecrementer[i] = new Thread(decrementer);

threadsIncrementer[i].start();
threadsDecrementer[i].start();
}

for (int i = 0; i < 100; i++) {
try {
threadsIncrementer[i].join();
threadsDecrementer[i].join();
} catch (InterruptedException e) {
e.printStackTrace();
}
}

for (int i = 0; i < atomicIntegerArray.length(); i++) {
if (atomicIntegerArray.get(i) != 0) {
System.out.println("Vector[" + i + "] : "
+ atomicIntegerArray.get(i));
}
}

System.out.println("Main : End of the example");
}

}