数据类：
package Thread.MyCommon;
public class Data {
public int num = 0;
public synchronized int getEven() {
++num;
Thread.yield();//让另外线程先执行,加大测试效果几率
++num;
return num;
}
}
线程类：
package Thread.MyCommon;
public class myThread implements Runnable {
private Data data;
public myThread(Data d) {
data = d;
}
@Override
public void run() {
while (true)
{
int val = data.getEven();
if (val % 2 != 0) {
System.out.println(val + " not even!");
}
}
}
}
主线程类：
package Thread.MyCommon; import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors; public class Main { public static void main(String[] args) {
Data data=new Data();//多个线程操作的是同一个对象
ExecutorService executorService=Executors.newCachedThreadPool();
for (int i = 0; i < 10; i++) {
executorService.execute(new myThread(data));
}
executorService.shutdown();//关闭线程池，如果不关闭线程池将一直运行。
}
}
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可以将同步代码改用lock方式：
package Thread.MyCommon; import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock; public class Data { public int num = 0; Lock lock = new ReentrantLock(); public int getEven() {
lock.lock();
try {
++num;
Thread.yield();// 让另外线程先执行,加大测试几率
++num;
return num;// 一定要在unlock之前return，否则数据不同步
} finally {
lock.unlock();
}
// return num;//不能在unlock之后return，否则数据不同步
}
}
或者改成 synchronized (this)
package Thread.MyCommon; import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock; public class Data { public int num = 0; Lock lock = new ReentrantLock(); public int getEven() {
synchronized (this) {
++num;
Thread.yield();// 让另外线程先执行,加大测试几率
++num;
return num;// 一定要在unlock之前return，否则数据不同步
}
}
}
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以下写法，虽然已经同步，但是读取方法不能保证数据是同步的偶数
package Thread.MyCommon; import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors; public class AtomicityTest implements Runnable { private int i = 0; public int getValue() {
return i;
} private synchronized void evenIncrement() {
i++;
Thread.yield();
i++;
} @Override
public void run() {
while (true)
evenIncrement();
} public static void main(String[] args) {
ExecutorService exec = Executors.newCachedThreadPool();
AtomicityTest at = new AtomicityTest();
exec.execute(at);
while (true) {
int val = at.getValue();
if (val % 2 != 0) {
System.out.println(val);
System.exit(0);
}
}
}
}