java并发

竞态条件示例：

public class Client {
    public static void main(String[] args) throws InterruptedException {
        MyRunnable myRunnable = new MyRunnable();
        Thread thread1 = new Thread(myRunnable, "线程1");
        Thread thread2 = new Thread(myRunnable, "线程2");
        Thread thread3 = new Thread(myRunnable, "线程3");

        thread1.start();
        thread2.start();
        thread3.start();


        thread1.join();
        thread2.join();
        thread3.join();

        System.out.println(myRunnable.getA());
    }


}

class MyRunnable implements Runnable {

    private int a = 0;

    @Override
    public void run() {
        for (int i = 0; i < 100000; i++) {
            ++a;
        }
    }

    public int getA() {
        return a;
    }
}

输出结果不一定，与预期不符。

解决方案1：内置锁，synchronized
解决方案2：显示锁，lock。unlock要放在finally里。