Android多線程研究（6）多線程之間數據隔離

在上一篇《Android多線程研究（5）——線程之間共享數據》中對線程之間的數據共享進行了學習和研究，這一篇我們來看看如何解決多個線程之間的數據隔離問題，什麼是數據隔離呢？比如說我們現在開啟了兩個線程，這兩個線程都要同時給同一個全局變量data賦值，各個線程操作它賦值後的變量數據，這裡就需要用到隔離。先看一段代碼：

import java.util.Random;  
      
      
public class ThreadLocalTest {  
    private static int data = 0;  
    public static void main(String[] args) {  
        for(int i=0; i<2; i++){  
            new Thread(new Runnable() {  
                      
                @Override
                public void run() {  
                    data = new Random().nextInt();  
                    System.out.println(Thread.currentThread().getName() +  
                            " has put data: " + data);  
                    new A().get();  
                    new B().get();  
                }  
            }).start();  
        }  
    }  
          
    static class A{  
        public int get(){  
            System.out.println("A from " + Thread.currentThread().getName() +  
                    " has get data: " + data);  
            return data;  
        }  
    }  
          
    static class B{  
        public int get(){  
            System.out.println("B from " + Thread.currentThread().getName() +  
                    " has get data: " + data);  
            return data;  
        }  
    }  
}

運行結果：

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從上面我們可以看到Thread-0和Thread-1都在操作變量data,但是兩個線程之間沒有做到對數據操作的隔離，所以輸出結果中兩個線程共用了一個data變量。

我們將上面代碼修改如下：

import java.util.HashMap;  
import java.util.Map;  
import java.util.Random;  
      
      
public class ThreadLocalTest {  
    //private static int data = 0;  
    private static Map<Thread, Integer> map = new HashMap<Thread, Integer>();  
    public static void main(String[] args) {  
        for(int i=0; i<2; i++){  
            new Thread(new Runnable() {  
                      
                @Override
                public void run() {  
                    //data = new Random().nextInt();  
                    int data = new Random().nextInt();  
                    map.put(Thread.currentThread(), data);  
                    System.out.println(Thread.currentThread().getName() +  
                            " has put data: " + data);  
                    new A().get();  
                    new B().get();  
                }  
            }).start();  
        }  
    }  
          
    static class A{  
        public int get(){  
            System.out.println("A from " + Thread.currentThread().getName() +  
                    " has get data: " + map.get(Thread.currentThread()));  
            return map.get(Thread.currentThread());  
        }  
    }  
          
    static class B{  
        public int get(){  
            System.out.println("B from " + Thread.currentThread().getName() +  
                    " has get data: " + map.get(Thread.currentThread()));  
            return  map.get(Thread.currentThread());  
        }  
    }  
}