ThreadLocal的简单使用(读书笔记)

Posted 2020-08-24 Darcy_wang

     从ThreadLocal的名字上可以看到,这是一个线程局部变量,也就是说,只有当前线程可以访问,既然是只有当前线程可以访问的数据,自然是线程安全的.

public class ThreadLocalDemo {
    private static ThreadLocal<SimpleDateFormat> t1 = new ThreadLocal<>();

    public static class ParseDate implements Runnable {
        int i = 0;

        public ParseDate(int i) {
            this.i = i;
        }

        /**
         * When an object implementing interface <code>Runnable</code> is used
         * to create a thread, starting the thread causes the object‘s
         * <code>run</code> method to be called in that separately executing
         * thread.
         * <p>
         * The general contract of the method <code>run</code> is that it may
         * take any action whatsoever.
         *
         * @see Thread#run()
         */
        @Override
        public void run() {
            try {
                if (t1.get() == null)
                    t1.set(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));
                Date t = t1.get().parse("2015-03-29 19:29:" + i % 60);
                System.out.println(i + ":" + t);
            } catch (ParseException e) {
                e.printStackTrace();
            }
        }

    }

    public static void main(String[] args) {
        ExecutorService es = Executors.newFixedThreadPool(10);
        for (int i = 0; i < 1000; i++) {
            es.execute(new ParseDate(i));
        }

    }
}

     从这里也可以看到,为每一个线程人手分配一个对象工作并不是有ThreadLocal来完成的.而是需要在应用层面保证的,如果在应用上为每一个线程分配了相同的对象实例,那么ThreadLocal也不能保证线程安全,