关于lock锁

关于lock锁

在 jdk1.5 之后，并发包中新增了 Lock 接口(以及相关实现类)用来实现锁功能，Lock 接口提供了与 synchronized 关键字类似的同步功能，但需要在使用时手动获取锁和释放锁。

lock锁 也叫显示锁 

大家看下这个lock锁:

lock是个接口

 这个接口下面很多锁：

对于lock锁的使用，实现生产者消费者模式的：

package com.toov5.thread;

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

//共享对象
class ResLock {
    public boolean flag = true;
    public String sex;
    public String name;
    public Lock lock = new ReentrantLock();
}
class inputThreadLock extends Thread {
    public ResLock res;

    public inputThreadLock(ResLock res) {
        this.res = res;
    }
    @Override
    public void run() {
        int count = 0;
        while (true) {
            try {
                res.lock.lock();
                if (count == 0) {
                    res.name = "lucy";
                    res.sex = "girl";
                } else {
                    res.name = "Jack";
                    res.sex = "boy";
                }
            count = (count + 1) % 2;
            } catch (Exception e) {
            }finally{
                res.lock.unlock();  //释放锁写在finally里面
            }
        
        }
    }
}
class readThreadLock extends Thread {
    public ResLock res;

    public readThreadLock(ResLock res) {
        this.res = res;
    }
    @Override
    public void run() {
        while (true) {
            try {
                res.lock.lock();
                System.out.println(res.name + "," + res.sex);
                
            } catch (Exception e) {
                e.printStackTrace();
            }finally {
                res.lock.unlock();
            }
            
        }
    }
}
public class LockTest {
    public static void main(String[] args) {
        Res res = new Res();
        inputThread inputThread = new inputThread(res);
        readThread  readThread = new readThread(res);
        inputThread.start();
        readThread.start();
    }    
}

注意 unlock写到finally里面哦

然后lock锁里面的 类似于 notify 和 wait的  Condition

 Condition的功能类似于在传统的线程技术中的,Object.wait()和Object.notify()的功能。

使用方法：

package com.toov5.thread;

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

//共享对象
class ResLock {
    public boolean flag = true;
    public String sex;
    public String name;
    public Lock lock = new ReentrantLock();
    public Condition condition  = lock.newCondition();
}
class inputThreadLock extends Thread {
    public ResLock res;

    public inputThreadLock(ResLock res) {
        this.res = res;
    }
    @Override
    public void run() {
        if (res.flag) {
            try {
                res.condition.await();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        int count = 0;
        while (true) {
            
            try {
                res.lock.lock();
                if (count == 0) {
                    res.name = "lucy";
                    res.sex = "girl";
                } else {
                    res.name = "Jack";
                    res.sex = "boy";
                }
            count = (count + 1) % 2;
            res.flag=true;
            res.condition.signal();
            } catch (Exception e) {
            }finally{
                res.lock.unlock();  //释放锁写在finally里面
            }
        
        }
    }
}
class readThreadLock extends Thread {
    public ResLock res;

    public readThreadLock(ResLock res) {
        this.res = res;
    }
    @Override
    public void run() {
        while (true) {
            try {
                res.lock.lock();
                if (res.flag) {
                    res.condition.await();
                }
                System.out.println(res.name + "," + res.sex);
                res.condition.signal();
            } catch (Exception e) {
                e.printStackTrace();
            }finally {
                res.lock.unlock();
            }
            
        }
    }
}
public class LockTest {
    public static void main(String[] args) {
        Res res = new Res();
        inputThread inputThread = new inputThread(res);
        readThread  readThread = new readThread(res);
        inputThread.start();
        readThread.start();
    }    
}

执行结果：

Lock与synchronized 关键字的区别

Lock 接口可以尝试非阻塞地获取锁 当前线程尝试获取锁。如果这一时刻锁没有被其他线程获取到，则成功获取并持有锁。
Lock 接口能被中断地获取锁 与 synchronized 不同，获取到锁的线程能够响应中断，当获取到的锁的线程被中断时，中断异常将会被抛出，同时锁会被释放。

Lock 接口在指定的截止时间之前获取锁，如果截止时间到了依旧无法获取锁，则返回。

 

synchronize重量级锁  不可控制 释放锁  遇到异常 或者代码执行完毕后 释放锁

lock轻量级  可控释放锁 更灵活一些  lock是1.5出来的 比synchronize晚 弥补了一些不足 还有读写锁 重入锁 功能要强大一些