013.多线程-ThreadLocal

一时失言乱红尘 2021-10-06 15:32 317阅读 0赞

为每一个线程提供一个局部变量。

## code of demo: ##

*  创建三个线程，分别打印递增的IDS

### 错误demo ###

package cn.qbz.thread;
    
    /** * @Author: 花生米 * @Date: 2018/11/16 18:15 */
    public class ThreadLocalTest { 
        public static void main(String[] args) { 
            //创建三个线程，每个线程均获得其IDS
            Ids ids = new Ids();
            GetIds t1 = new GetIds(ids);
            GetIds t2 = new GetIds(ids);
            GetIds t3 = new GetIds(ids);
    
            t1.start();
            t2.start();
            t3.start();
        }
    
    }
    
    class GetIds extends Thread { 
        private Ids ids;
    
        public GetIds(Ids ids) { 
            this.ids = ids;
        }
    
        @Override
        public void run() { 
            for (int i = 0; i < 3; i++) { 
                System.out.println(getName() + "..." + ids.nextId());
            }
        }
    }
    
    class Ids { 
        private int id = 0;
    
        public int nextId() { 
            return id++;
        }
    }

![TeamViewer_2018-11-16_18-25-36.png][]

--------------------

### 通过创建多个被执行对象来解决 ###

package cn.qbz.thread;
    
    /** * @Author: 花生米 * @Date: 2018/11/16 18:15 */
    public class ThreadLocalTest { 
        public static void main(String[] args) { 
            //创建三个线程，每个线程均获得其IDS
            Ids ids1 = new Ids();
            Ids ids2 = new Ids();
            Ids ids3 = new Ids();
            GetIds t1 = new GetIds(ids1);
            GetIds t2 = new GetIds(ids2);
            GetIds t3 = new GetIds(ids3);
    
            t1.start();
            t2.start();
            t3.start();
        }
    
    }
    
    class GetIds extends Thread { 
        private Ids ids;
    
        public GetIds(Ids ids) { 
            this.ids = ids;
        }
    
        @Override
        public void run() { 
            for (int i = 0; i < 3; i++) { 
                System.out.println(getName() + "..." + ids.nextId());
            }
        }
    }
    
    class Ids { 
        private int id = 0;
    
        public int nextId() { 
            return id++;
        }
    }

![TeamViewer_2018-11-16_18-28-26.png][]

--------------------

### 使用Thread Local包装Ids ###

package cn.qbz.thread;
    
    /** * @Author: 花生米 * @Date: 2018/11/16 18:15 */
    public class ThreadLocalTest { 
        public static void main(String[] args) { 
            //创建三个线程，每个线程均获得其IDS
            Ids ids = new Ids();
            GetIds t1 = new GetIds(ids);
            GetIds t2 = new GetIds(ids);
            GetIds t3 = new GetIds(ids);
    
            t1.start();
            t2.start();
            t3.start();
        }
    
    }
    
    class GetIds extends Thread { 
        private Ids ids;
    
        public GetIds(Ids ids) { 
            this.ids = ids;
        }
    
        @Override
        public void run() { 
            for (int i = 0; i < 3; i++) { 
                System.out.println(getName() + "..." + ids.nextId());
            }
        }
    }
    
    class Ids { 
        ThreadLocal<Integer> threadLocal = ThreadLocal.withInitial(() -> 0);
    
        public int nextId() { 
            threadLocal.set(threadLocal.get() + 1);
            return threadLocal.get();
        }
    }

![TeamViewer_2018-11-16_18-35-43.png][]

[TeamViewer_2018-11-16_18-25-36.png]: http://upyun.qubianzhong.cn/picture/TeamViewer_2018-11-16_18-25-36.png
[TeamViewer_2018-11-16_18-28-26.png]: http://upyun.qubianzhong.cn/picture/TeamViewer_2018-11-16_18-28-26.png
[TeamViewer_2018-11-16_18-35-43.png]: http://upyun.qubianzhong.cn/picture/TeamViewer_2018-11-16_18-35-43.png