浅解ThreadLocal

今天药忘吃喽~ 2024-03-27 01:54 70阅读 0赞

我们知道的是synchronized能够解决线程安全中的内存可见性问题（让每个线程读取到的变量一致），而ThreadLocal恰好相反，它是让每个线程都有处理任务过程中不同的值。

![9d000daa89a433f90374e5717ba61130.png][]

而我们通过代码发现他确实可以实现这样的功能

package executor;
    
    /**
     * @author tongchen
     * @create 2023-02-10 22:48
     */
    public class TestThreadLocal {
        public static void main(String[] args) {
            ThreadLocal<Integer> threadLocal = new ThreadLocal<>();
            ThreadLocal<Integer> local = new ThreadLocal<>();
             Thread t1 =new Thread(()->{
                        int count =30;
                        threadLocal.set(count);
                 System.out.println(threadLocal.get());
             });
             Thread t2 =new Thread(()->{
                        int count =35;
                        threadLocal.set(count);
                 System.out.println(threadLocal.get());
             });
             Thread t3 =new Thread(()->{
                        int count =40;
                        threadLocal.set(count);
                 System.out.println(threadLocal.get());
             });
            t1.start();
            t2.start();
            t3.start();
        }
    }

![514d0dd2249b306c5fda50c6bde66e00.png][]

事实上，它是在底层维护了一个map，那作为map，他为什么创建时只传入一个参数呢？

我们通过观察源码发现，他的key事实上是当前线程

![7b77a9ad37166d9406aab415547e0557.png][]

![a4a8b71ab5fde9086ec6a525fcd7e443.png][]

[9d000daa89a433f90374e5717ba61130.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/27/8255f031fbe94432b5b79f965f61d999.png
[514d0dd2249b306c5fda50c6bde66e00.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/27/3440b51dcd2b48d38e0a9fdbac42a221.png
[7b77a9ad37166d9406aab415547e0557.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/27/047f6f5e63f44e52af385b8b16a4f8ad.png
[a4a8b71ab5fde9086ec6a525fcd7e443.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/03/27/528f5ccabf2242af8d4b112c39d6be95.png