线程学习--（十三）重写锁、读写锁、锁的高级深化

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线程学习--（十三）重写锁、读写锁、锁的高级深化

2024-10-05 21:48:39 212人阅读

一、Concurrent.util常用类

1.CountDownLacth使用：

他经常用于监听某些初始化操作，等初始化执行完毕后，通知主线程继续工作

package thread3;

import java.util.concurrent.CountDownLatch;

public class UseCountDownLatch {
    public static void main(String[] args) {
        
    final CountDownLatch countDown = new CountDownLatch(2);
        
        Thread t1 = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    System.out.println("进入线程t1" + "等待其他线程处理完成...");
                    countDown.await();
                    System.out.println("t1线程继续执行...");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        },"t1");
        
        Thread t2 = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    System.out.println("t2线程进行初始化操作...");
                    Thread.sleep(3000);
                    System.out.println("t2线程初始化完毕，通知t1线程继续...");
                    countDown.countDown();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
        Thread t3 = new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    System.out.println("t3线程进行初始化操作...");
                    Thread.sleep(4000);
                    System.out.println("t3线程初始化完毕，通知t1线程继续...");
                    countDown.countDown();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
        
        t1.start();
        t2.start();
        t3.start();
    }
}

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2.CyclicBarrier使用

假设有一个场景：每个线程代表一个跑步运动员，当运动员都准备好后，才一起出发，只要有一个人没有准备好，大家都等待。

package com.bjsxt.height.concurrent019;
import java.io.IOException;  
import java.util.Random;  
import java.util.concurrent.BrokenBarrierException;  
import java.util.concurrent.CyclicBarrier;  
import java.util.concurrent.ExecutorService;  
import java.util.concurrent.Executors; 
public class UseCyclicBarrier {

    static class Runner implements Runnable {  
        private CyclicBarrier barrier;  
        private String name;  
        
        public Runner(CyclicBarrier barrier, String name) {  
            this.barrier = barrier;  
            this.name = name;  
        }  
        @Override  
        public void run() {  
            try {  
                Thread.sleep(1000 * (new Random()).nextInt(5));  
                System.out.println(name + " 准备OK.");  
                barrier.await();  
            } catch (InterruptedException e) {  
                e.printStackTrace();  
            } catch (BrokenBarrierException e) {  
                e.printStackTrace();  
            }  
            System.out.println(name + " Go!!");  
        }  
    } 
    
    public static void main(String[] args) throws IOException, InterruptedException {  
        CyclicBarrier barrier = new CyclicBarrier(3);  // 3 
        ExecutorService executor = Executors.newFixedThreadPool(3);  
        
        executor.submit(new Thread(new Runner(barrier, "zhangsan")));  
        executor.submit(new Thread(new Runner(barrier, "lisi")));  
        executor.submit(new Thread(new Runner(barrier, "wangwu")));  
  
        executor.shutdown();  
    }  
  
}

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3. Callable和Futured使用

其实就是上篇实现的future模式，jdk给予我们一个实现的封装，使用非常简单

future模式非常适合在处理很耗时很长的业务逻辑进行实现，可以有效地减小系统响应时间，提高系统吞吐量。

package readwritlock;

import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Executor;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.FutureTask;

public class UseFuture implements Callable<String>{
    private String para;
    
    public UseFuture(String para){
        this.para=para;
    }
    
    /**
     * 这里是真实的业务逻辑，其执行可能很慢
     */
    @Override
    public String call() throws Exception {
        Thread.sleep(3000);
        String result=this.para+"处理完成";
        return result;
    }
    
    public static void main(String[] args) {
        
        try {
            String queryStr="query";
            //构造FutureTask，并且传入需要真正进行业务逻辑处理的类，该类一定要实现Callable接口的类
            FutureTask<String> future=new FutureTask<String>(new UseFuture(queryStr));
            //创建一个固定线程的线程池且线程数为1，
            ExecutorService executor=Executors.newFixedThreadPool(1);
            //这里提交任务future，开启线程并执行call方法
            //submit和execute的区别：
            //第一点submit可以传入实现Callable接口的实例对象，
            //第二点是submit方法有返回值
            Future f=executor.submit(future);
            System.out.println("请求完毕");
            System.out.println(future.get()); //获取成功返回null值（任务处理完成返回）
            System.out.println(f.get()); //获取返回结果
            
            executor.shutdown();
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (ExecutionException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

}

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5.ReentrantLock(重入锁)

重入锁，在需要进行同步的代码部分加上锁定，但不要忘记最后一定要释放锁定，不然会造成永远无法释放，其他线程永远进不来的结果

package com.bjsxt.height.lock020;

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

public class UseReentrantLock {
    
    private Lock lock = new ReentrantLock();
    
    public void method1(){
        try {
            lock.lock();
            System.out.println("当前线程:" + Thread.currentThread().getName() + "进入method1..");
            Thread.sleep(1000);
            System.out.println("当前线程:" + Thread.currentThread().getName() + "退出method1..");
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            
            lock.unlock();
        }
    }
    
    public void method2(){
        try {
            lock.lock();
            System.out.println("当前线程:" + Thread.currentThread().getName() + "进入method2..");
            Thread.sleep(2000);
            System.out.println("当前线程:" + Thread.currentThread().getName() + "退出method2..");
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            
            lock.unlock();
        }
    }
    
    public static void main(String[] args) {

        final UseReentrantLock ur = new UseReentrantLock();
        Thread t1 = new Thread(new Runnable() {
            @Override
            public void run() {
                ur.method1();
                ur.method2();
            }
        }, "t1");

        t1.start();
        try {
            Thread.sleep(10);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        //System.out.println(ur.lock.getQueueLength());
    }
    
    
}

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还记得我们在使用synchronized的时候，如果需要多线程间进行写作工作则需要Object的wait()和notify(),notifyAll() 方法进行配合合作，

那么同样，我们在使用lock的时候，可以使用一个新的等待通知的类，他就是Condition。这个condition一定是针对具体某一把锁的。也就是只有锁的基础上才会产生Condition

package com.bjsxt.height.lock020;

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

public class UseCondition {

    private Lock lock = new ReentrantLock();
    private Condition condition = lock.newCondition();
    
    public void method1(){
        try {
            lock.lock();
            System.out.println("当前线程：" + Thread.currentThread().getName() + "进入等待状态..");
            Thread.sleep(3000);
            System.out.println("当前线程：" + Thread.currentThread().getName() + "释放锁..");
            condition.await();    // Object wait
            System.out.println("当前线程：" + Thread.currentThread().getName() +"继续执行...");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
    
    public void method2(){
        try {
            lock.lock();
            System.out.println("当前线程：" + Thread.currentThread().getName() + "进入..");
            Thread.sleep(3000);
            System.out.println("当前线程：" + Thread.currentThread().getName() + "发出唤醒..");
            condition.signal();        //Object notify
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
    
    public static void main(String[] args) {
        
        final UseCondition uc = new UseCondition();
        Thread t1 = new Thread(new Runnable() {
            @Override
            public void run() {
                uc.method1();
            }
        }, "t1");
        Thread t2 = new Thread(new Runnable() {
            @Override
            public void run() {
                uc.method2();
            }
        }, "t2");
        t1.start();

        t2.start();
    }
    
    
    
}

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多Condition

我们可以通过一个Lock对象产生多个Condition进行多线程间的交互，非常的灵活，可以使得部分需要唤醒的线程唤醒，其他线程则继续等待通知。

package com.bjsxt.height.lock020;

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

public class UseManyCondition {

    private ReentrantLock lock = new ReentrantLock();
    private Condition c1 = lock.newCondition();
    private Condition c2 = lock.newCondition();
    
    public void m1(){
        try {
            lock.lock();
            System.out.println("当前线程：" +Thread.currentThread().getName() + "进入方法m1等待..");
            c1.await();
            System.out.println("当前线程：" +Thread.currentThread().getName() + "方法m1继续..");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
    
    public void m2(){
        try {
            lock.lock();
            System.out.println("当前线程：" +Thread.currentThread().getName() + "进入方法m2等待..");
            c1.await();
            System.out.println("当前线程：" +Thread.currentThread().getName() + "方法m2继续..");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
    
    public void m3(){
        try {
            lock.lock();
            System.out.println("当前线程：" +Thread.currentThread().getName() + "进入方法m3等待..");
            c2.await();
            System.out.println("当前线程：" +Thread.currentThread().getName() + "方法m3继续..");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
    
    public void m4(){
        try {
            lock.lock();
            System.out.println("当前线程：" +Thread.currentThread().getName() + "唤醒..");
            c1.signalAll();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
    
    public void m5(){
        try {
            lock.lock();
            System.out.println("当前线程：" +Thread.currentThread().getName() + "唤醒..");
            c2.signal();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
    
    public static void main(String[] args) {
        
        
        final UseManyCondition umc = new UseManyCondition();
        Thread t1 = new Thread(new Runnable() {
            @Override
            public void run() {
                umc.m1();
            }
        },"t1");
        Thread t2 = new Thread(new Runnable() {
            @Override
            public void run() {
                umc.m2();
            }
        },"t2");
        Thread t3 = new Thread(new Runnable() {
            @Override
            public void run() {
                umc.m3();
            }
        },"t3");
        Thread t4 = new Thread(new Runnable() {
            @Override
            public void run() {
                umc.m4();
            }
        },"t4");
        Thread t5 = new Thread(new Runnable() {
            @Override
            public void run() {
                umc.m5();
            }
        },"t5");
        
        t1.start();    // c1
        t2.start();    // c1
        t3.start();    // c2
        

        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        t4.start();    // c1
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        t5.start();    // c2
        
    }
    
    
    
}

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6.ReentrantReadWriteLock（读写锁）

读写锁ReentrantReadWriteLock,其核心就是实现读写分离的锁。在高并发访问下，尤其是读多写少的情况下，性能要远高于重入锁。

之前学synchronized,ReentrantLock时，我们知道，同一时间，只能有一个线程进行访问被锁定的代码，那么读写锁则不同，其本质分成两个锁，即读锁、写锁，在读锁下，多线程可以并发的进行访问，但是在写锁的时候，只能一个一个的顺序访问

口诀：读读共享，写写互斥，读写互斥

package com.bjsxt.height.lock021;

import java.util.concurrent.locks.ReentrantReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock.ReadLock;
import java.util.concurrent.locks.ReentrantReadWriteLock.WriteLock;

public class UseReentrantReadWriteLock {

    private ReentrantReadWriteLock rwLock = new ReentrantReadWriteLock();
    private ReadLock readLock = rwLock.readLock();
    private WriteLock writeLock = rwLock.writeLock();
    
    public void read(){
        try {
            readLock.lock();
            System.out.println("当前线程:" + Thread.currentThread().getName() + "进入...");
            Thread.sleep(3000);
            System.out.println("当前线程:" + Thread.currentThread().getName() + "退出...");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            readLock.unlock();
        }
    }
    
    public void write(){
        try {
            writeLock.lock();
            System.out.println("当前线程:" + Thread.currentThread().getName() + "进入...");
            Thread.sleep(3000);
            System.out.println("当前线程:" + Thread.currentThread().getName() + "退出...");
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            writeLock.unlock();
        }
    }
    
    public static void main(String[] args) {
        
        final UseReentrantReadWriteLock urrw = new UseReentrantReadWriteLock();
        
        Thread t1 = new Thread(new Runnable() {
            @Override
            public void run() {
                urrw.read();
            }
        }, "t1");
        Thread t2 = new Thread(new Runnable() {
            @Override
            public void run() {
                urrw.read();
            }
        }, "t2");
        Thread t3 = new Thread(new Runnable() {
            @Override
            public void run() {
                urrw.write();
            }
        }, "t3");
        Thread t4 = new Thread(new Runnable() {
            @Override
            public void run() {
                urrw.write();
            }
        }, "t4");        
        
//        t1.start();
//        t2.start();
        
//        t1.start(); // R 
//        t3.start(); // W
        
        t3.start();
        t4.start();
        
        
        
        
        
        
        
        
    }
}