【ThreadLocal】使用ThreadLocal实现线程安全

非线程安全

public class UnSafeThreadLocalDemo {
    private int count = 0;

    public static void main(String[] args) {
        UnSafeThreadLocalDemo unSafeThreadLocalDemo = new UnSafeThreadLocalDemo();
        for (int i = 0; i < 5; i++) {
            int finalI = i;
            new Thread(new Runnable() {
                @Override
                public void run() {
                    unSafeThreadLocalDemo.process();
                    unSafeThreadLocalDemo.print(finalI);
                }
            }).start();
        }

    }

    public void process() {
        for (int i = 0; i < 10; i++) {
            count += 1;
            try {
                TimeUnit.MILLISECONDS.sleep(new Random().nextInt(10) + 10);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

    }

    public void print(int i) {
        System.out.println("count(" + i + ") = " + count);
    }
}

输出：

count(1) = 44
count(0) = 46
count(3) = 47
count(2) = 49
count(4) = 49

线程安全

public class SafeThreadLocalDemo {
    //    private int count = 0;
    private ThreadLocal<Integer> count = new ThreadLocal<Integer>() {
        protected Integer initialValue() {
            return 0;
        }
    };

    public void process() {
        for (int i = 0; i < 10; i++) {
            count.set(count.get() + 1);
            try {
                TimeUnit.MILLISECONDS.sleep(new Random().nextInt(10) + 10);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

    }

    public void print(int i) {
        System.out.println("count(" + i + ") = " + count.get());
    }

    public static void main(String[] args) {
        SafeThreadLocalDemo safeThreadLocalDemo = new SafeThreadLocalDemo();
        for (int i = 0; i < 5; i++) {
            int finalI = i;
            new Thread(new Runnable() {
                @Override
                public void run() {
                    safeThreadLocalDemo.process();
                    safeThreadLocalDemo.print(finalI);
                }
            }).start();
        }

    }
}

输出：

count(1) = 10
count(0) = 10
count(2) = 10
count(4) = 10
count(3) = 10