synchronized的使用方法和作用域

r囧r小猫 2021-10-13 17:22 312阅读 0赞

synchronized是保证多线程同步执行的关键字,它的用法有以下几种

public class ClassA {
    	
    	//放在方法 锁的是对象 和 synchronized(this)是一样的
    	public synchronized void lockMethod() {
    		System.out.println(Thread.currentThread().getName()+"\t 111 lockMethod");
    	}
    
    	
    	public void lockMethod_CodeBlockByThis() {
            //代码块 this锁的是对象
    		synchronized(this) {
    			System.out.println(Thread.currentThread().getName()+"\t 222 lockMethod_CodeBlockByThis");
    		}
    	}
    	
    	public void lockMethod_CodeBlockByClass() {
            //代码块 Class锁的是类，无论任何地方，任何类只要是锁的是同一个class，并发时都会等待
    		synchronized(ClassA.class) {
    			System.out.println(Thread.currentThread().getName()+"\t 333 lockMethod_CodeBlockByClass");
    			try {
    				Thread.sleep(2000);
    			} catch (InterruptedException e) {
    				e.printStackTrace();
    			}
    		}
    	}
    	
        //放在静态方法上，锁的是当前的class，此处的锁和synchronized(ClassA.class)是同样的
        public synchronized static void lockStaticMethod() {
    		System.out.println(Thread.currentThread().getName()+"\t 444 lockStaticMethod");
    	
    	}
    
    }

如上代码中：

lockMethod()和lockMethod\_CodeBlockByThis()是**方法锁**；

lockStaticMethod()和lockMethod\_CodeBlockByClass()是**类锁**；

方法锁与方法锁互斥，类锁与类锁互斥。

测试类

public class TestThread {
    
    	public static void main(String[] args) {
    		ClassA a = new ClassA();
    		ClassC c = new ClassC();
    		for (int i = 1; i < 1000; i++) {
    			new Thread(new Runnable() {
    
    				@Override
    				public void run() {
    					a.lockMethod();
    				}
    			}, "thread01-----").start();
    
    			new Thread(new Runnable() {
    
    				@Override
    				public void run() {
    					a.lockMethod_CodeBlockByThis();
    				}
    			}, "thread02=============").start();
    
    			new Thread(new Runnable() {
    
    				@Override
    				public void run() {
    					a.lockMethod_CodeBlockByClass();
    				}
    			}, "thread03>>>>>>>>>>>>>>>>>>>>>>>>").start();
    
    			new Thread(new Runnable() {
    
    				@Override
    				public void run() {
    					a.lockStaticMethod();
    				}
    			}, "thread04********").start();
    			
    			new Thread(new Runnable() {
    
    				@Override
    				public void run() {
    					c.lockMethod_CodeBlockByClass();
    				}
    			}, "thread05 》》》》》》 ").start();
    		}
    	}
    
    }

在其他方法中使用ClassA加锁

public class ClassC {
    
    	public void lockMethod_CodeBlockByClass() {
    		synchronized (ClassA.class) {
    			System.out.println(Thread.currentThread().getName() + "\t CCC ClassC lockMethod_CodeBlockByClass");
    			try {
    				Thread.sleep(500);
    			} catch (InterruptedException e) {
    				e.printStackTrace();
    			}
    		}
    	}
    
    }