十一、并发编程之Lock接口的认识与使用

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/qq_29479041/article/details/84840378

1、认识

2、优势

• Lock 类似于synchronized，具有相同的互斥性和内存可见性，但是更加灵活，加锁和放锁可以由使用者自己确定，Synchronized不需要显示地获取和释放锁，简单
• 可以方便的实行公平性
• 非阻塞的获取锁
• 能被中断的获取锁，synchronized锁可能出现异常而导致中断，无法释放锁，但是通过使用lock，可以直接将lock放在异常finally中，强制释放锁。
• 超时获取锁

3、使用

public class Sequence {
	private int value  ;
	Lock lock = new ReentrantLock();
	
	public  int getNext() {
		//lock放在这里是锁不住的，所有线程得共用一把锁才锁的住，所有锁得放外边
		//Lock lock = new ReentrantLock();
		lock.lock();//获取锁
		int a = value++;
		lock.unlock();//释放锁
		return a;
	}

	public static void main(String[] args) {
		Sequence sequence = new Sequence();
		//第一个线程
		new Thread(new Runnable() {
			@Override
			public void run() {
				while(true) {
					System.out.println(Thread.currentThread().getName()+"      ----->"+sequence.getNext());
					try {
						Thread.sleep(100);
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
				}
			}
		}).start();
		//第二个线程
		new Thread(new Runnable() {
			@Override
			public void run() {
				while(true) {
					System.out.println(Thread.currentThread().getName()+"      ----->"+sequence.getNext());
					try {
						Thread.sleep(100);
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
				}
			}
		}).start();
		//第三个线程
		new Thread(new Runnable() {
			@Override
			public void run() {
				while(true) {
					System.out.println(Thread.currentThread().getName()+"      ----->"+sequence.getNext());
					try {
						Thread.sleep(100);
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
				}
			}
		}).start();
	}
}

4、实现一个普通的锁

public class MyLock implements Lock{
	private boolean isLocked = false;
	//加锁
	@Override
	public synchronized void lock() {
		// 第一个线程进来不等待，其他线性进来等待
		while(isLocked) {
			try {
				wait();
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		}
		isLocked = true;
	}
	//释放锁
	@Override
	public synchronized void unlock() {
		isLocked = false;//释放锁
		notifyAll();//唤醒其他线程
	}
	//中断锁
	@Override
	public void lockInterruptibly() throws InterruptedException {

	}

	@Override
	public boolean tryLock() {
		return false;
	}

	@Override
	public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {
		return false;
	}

	@Override
	public Condition newCondition() {
		return null;
	}
}

public class Sequence {
	private MyLock lock = new MyLock();
	private int value;
	
	public  int getNext() {
		lock.lock();//获取锁
		value++;
		lock.unlock();//释放锁
		return value;
	}

	public static void main(String[] args) {
		Sequence sequence = new Sequence();
		//第一个线程
		new Thread(new Runnable() {
			@Override
			public void run() {
				while(true) {
					System.out.println(Thread.currentThread().getName()+"      ----->"+sequence.getNext());
					try {
						Thread.sleep(100);
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
				}
			}
		}).start();
		
		//第二个线程
		new Thread(new Runnable() {
			@Override
			public void run() {
				while(true) {
					System.out.println(Thread.currentThread().getName()+"      ----->"+sequence.getNext());
					try {
						Thread.sleep(100);
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
				}
			}
		}).start();
		//第三个线程
		new Thread(new Runnable() {
			@Override
			public void run() {
				while(true) {
					System.out.println(Thread.currentThread().getName()+"      ----->"+sequence.getNext());
					try {
						Thread.sleep(100);
					} catch (InterruptedException e) {
						e.printStackTrace();
					}
				}
			}
		}).start();
	}
}

5、实现一个重入锁

public class MyLock implements Lock {
	private boolean isLocked = false;//是否锁住
	private Thread lockBy = null;//拿到锁的线程
	private int lockCount = 0;//锁的数量

	@Override
	public synchronized void lock() {
		Thread currentThread = Thread.currentThread(); // 当前线程
		while (isLocked && currentThread != lockBy)//锁住了并且线程不等于当前线程
			try {
				wait();
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
		isLocked = true;
		lockBy = currentThread;
		lockCount ++; // 1   2  3拿到锁的数量想加
	}
	
	@Override
	public synchronized void unlock() {
		if(lockBy == Thread.currentThread()) {
			lockCount --;  //2  1  0
			if(lockCount == 0) {//释放所有锁之后
				notify();
				isLocked = false;
			}
		}
	}

	@Override
	public void lockInterruptibly() throws InterruptedException {
		
	}

	@Override
	public boolean tryLock() {
		return false;
	}

	@Override
	public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {
		return false;
	}

	@Override
	public Condition newCondition() {
		return null;
	}
}

public class Demo {
	MyLock lock = new MyLock();
	public void a() {
		lock.lock();
		System.out.println("a");
		b();
		lock.unlock();
	}
	public void b() {
		lock.lock();
		System.out.println("b");
		c();
		lock.unlock();
	}
	public void c() {
		lock.lock();
		System.out.println("c");
		lock.unlock();
	}
	public static void main(String[] args) {
		Demo d = new Demo();
		new Thread(new Runnable() {
			@Override
			public void run() {
				d.a();
			}
		}).start();
		new Thread(new Runnable() {
			@Override
			public void run() {
				d.b();
			}
		}).start();
	}
}