java多线程Lock关键字、Condition

灰太狼 2022-03-20 09:59 340阅读 0赞

一、Lock关键字相对于传统锁synchronized更加面向对象

1、示例：在多线程情况下，按顺序输出指定字符串

定义一个类专门用于输出字符串

public class ThreadLockDemo {
           int len = s.length();
    		for (int i = 0; i < len; i++) {
    			System.out.print(s.charAt(i));
    		}
    		System.out.println();
    
    	}
    
    }

多线程访问:

public static void main(String[] args) {
    
    		ThreadLockDemo threadLockDemo = new ThreadLockDemo();
    
    		new Thread(new Runnable() {
    			@Override
    			public void run() {
    				for (int i = 0; i < 10; i++) {
    					try {
    						Thread.sleep(10);
    					} catch (InterruptedException e) {
    						e.printStackTrace();
    					}
    					threadLockDemo.printLetter("liucui");
    				}
    			}
    		}).start();
    
    		new Thread(new Runnable() {
    			@Override
    			public void run() {
    				for (int i = 0; i < 10; i++) {
    					try {
    						Thread.sleep(10);
    					} catch (InterruptedException e) {
    						e.printStackTrace();
    					}
    					threadLockDemo.printLetter("wuchengfeng");
    				}
    			}
    		}).start();
    
    	}

输出结果：

wuchengfenliucuig

liucui  
wuchengfeng  
wuchengfeng  
liucui  
wluiucui  
chengfeng  
wuchengfeng  
liucui  
wliucuuchengfeng  
i  
liucui  
wuchengfeng  
wliucui  
uchengfeng  
wucliucuihengf  
eng  
wluiucui  
chengfeng  
由控制台输出可以看出，printLetter方法在多线程访问下被打断，导致输出混乱，这时候使用lock关键字可以有效的解决这个问题

重新改写ThreadLockDemo

public class ThreadLockDemo {
    
    	Lock lock = new ReentrantLock();
    
    	public void printLetter(String s) {
    		//加锁
    		lock.lock();
    		try {
    			int len = s.length();
    			for (int i = 0; i < len; i++) {
    				System.out.print(s.charAt(i));
    			}
    			System.out.println();
    		} finally {
    			//锁释放
    			lock.unlock();
    		}
    	}
    
    }

liucui  
wuchengfeng  
liucui  
wuchengfeng  
liucui  
wuchengfeng  
wuchengfeng  
liucui  
liucui  
wuchengfeng  
liucui  
wuchengfeng  
wuchengfeng  
liucui  
liucui

二、ReadWriteLock读写锁，共享数据的时候，多个线程只有一个线程可以写数据，多个线程可以读数据

public class ThreadLockDemo {
    	
    	ReadWriteLock  readWriteLock=new ReentrantReadWriteLock();
    
    	public void readData() {
    		//保证多个线程可以同时读数据
    		readWriteLock.readLock().lock();
    		System.out.println(Thread.currentThread().getName()+"------------开始读数据--------------------------");
    		try {
    			Thread.sleep((long)Math.random()*1000);
    		} catch (Exception e) {
               e.printStackTrace();
    		}
    		System.out.println(Thread.currentThread().getName()+"------------数据读完了--------------------------");
    		readWriteLock.readLock().unlock();
    	}
    	
    
    	public void writeData() {
    		//保证多个线程同时只有一个线程可以写数据
    		readWriteLock.writeLock().lock();
    		System.out.println(Thread.currentThread().getName()+"#############开始写数据#############-");
    		try {
    			Thread.sleep((long)Math.random()*1000);
    		} catch (Exception e) {
               e.printStackTrace();
    		}
    		System.out.println(Thread.currentThread().getName()+"#############数据写完了#############");
    		readWriteLock.writeLock().unlock();
    	}
    
    
    }

三、Condition替换传统的wait、notify功能

static class ThreadSubMain {
    
    		private boolean isWait = true;
    
    		Lock lock = new ReentrantLock();
    		Condition condition = lock.newCondition();
    
    		/// 子线程循环20次
    		void subExcute(int i) {
    			lock.lock();
    			while (!isWait) {
    				try {
    					condition.await();//类似this.wait()
    				} catch (Exception e) {
    					e.printStackTrace();
    				}
    			}
    
    			for (int j = 0; j < 2; j++) {
    				System.out.println("第" + i + "个，第" + j + "子线程--->" + Thread.currentThread().getName());
    			}
    			// 当子线程执行两次后，改变标识符，唤醒主线程执行；
    			isWait = false;
    			condition.signal();
    			lock.unlock();
    		}
    
    		/// 主线程循环10次
    		void mainExcute() {
    			lock.lock();
    			for (int i = 0; i < 10; i++) {
    				while (isWait) {
    					try {
    						condition.await();
    					} catch (InterruptedException e) {
    						e.printStackTrace();
    					}
    					System.out.println("第" + i + "个主线程--->" + Thread.currentThread().getName());
    				}
    				// 当主线程执行一次后，改变标识符，唤醒主子线程
    				isWait = true;
    				condition.signal();/类似this.notify()
    			}
    			lock.unlock();
    		}
    	}

public static void main(String[] args) {
    		ThreadSubMain threadSubMain = new ThreadSubMain();
    
    		new Thread(new Runnable() {
    			@Override
    			public void run() {
    				for (int i = 0; i < 10; i++) {
    					threadSubMain.subExcute(i);
    				}
    			
    			}
    		}).start();	
            
    		threadSubMain.mainExcute();
    	
    	}