實例級別的鎖

實例代碼

@Slf4j
public class AddCompareDemo {
    private int a, b;

    public void add() {
        for (int i = 0; i < 10000; i++) {
            a++;
            b++;
        }
    }

    public void compare() {
        for (int i = 0; i < 10000; i++) {
            if (a < b) {
                log.info("a:{},b:{},{}", a, b, a > b);
            }
        }
    }

}

執行

@SpringBootApplication
public class NewdemoApplication {

    public static void main(String[] args) throws Exception {
        SpringApplication.run(NewdemoApplication.class, args);
        AddCompareDemo demo = new AddCompareDemo();
        new Thread(() -> {
            demo.add();
        }).start();
        new Thread(() -> {
            demo.compare();
        }).start();
    }

}

執行結果

 INFO 39336 --- [      Thread-30] com.example.newdemo.AddCompareDemo       : a:5262,b:5894,true

解決

這是同一個實例之間的行程安全問題。在方法上增加synchronize欄位

@Slf4j
public class AddCompareDemo {
    private int a, b;

    public synchronized void add() {
        for (int i = 0; i < 10000; i++) {
            a++;
            b++;
        }
    }

    public synchronized void compare() {
        for (int i = 0; i < 10000; i++) {
            if (a < b) {
                log.info("a:{},b:{},{}", a, b, a > b);
            }
        }
    }
}

即可解決問題

類級別

代碼

public class ClassLevelSyncDemo {

    private static int data;//類基本靜態欄位

    public synchronized void count() {//此處預設是實例級別的鎖
        data++;
    }

    public static int getData() {
        return data;
    }
}

執行

@SpringBootApplication
@Slf4j
public class NewdemoApplication {

    public static void main(String[] args) throws Exception {
        SpringApplication.run(NewdemoApplication.class, args);
        IntStream.rangeClosed(1, 100000).parallel().forEach(i ->
        {
            new ClassLevelSyncDemo().count();
        });
        log.info("" + ClassLevelSyncDemo.getData());

    }

}

執行結果

28988 不是100000.

解決方法

 1 public class ClassLevelSyncDemo {
 2 
 3     private static int data;//類基本靜態欄位
 4     private static Object object = new Object();
 5 
 6     public void count() {
 7         synchronized (object) {
 8             data++;
 9         }
10     }
11 
12     public static int getData() {
13         return data;
14     }
15 }