架构师养成记--14.重入锁ReentrantLock 和 读写锁 ReentrantReadWriteLock

ReentrantLock

有嗅探锁定和多路分支等功能，其实就是synchronized，wait，notify的升级。

this锁定当前对象不方便，于是就有了用new Object()来作为锁的解决方案，后面jdk干脆就提供了一个Lock类。

伪代码：

Lock lock = new ReentrantLock();//新建一个lock

Condition condition = lock.newCondition();//获取条件

method1(){

　　try{

　　　　lock.lock();

　　　　代码块；

　　　　lock.unlock();

　　　　后续代码块；

　　}

}

method2(){

　　try{

　　　　lock.lock();

　　　　代码块；

　　　　lock.signal();

　　}

}

单condition操作：

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..");
            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();
    }
    
    
    
}

执行结果：

 
解释：线程1调用method1方法，线程2调用同一对象的method2方法，线程1先启动，线程1获取锁，进入method1的代码块，线程2也启动了，单是线程2被锁定，直到线程1发出lock.unlock()了，线程1才将锁释放，这时线程2获取锁，执行method2的代码块，线程2发出lock.signal(); 线程1才继续执行后续代码块。

 多condition操作：

import java.util.concurrent.locks.Condition;
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
        
    }
    
    
    
}

执行结果：

解释：t1、t2线程都是用第一个condition c1，t3线程用第二个condition c2，t4线程发出c1.signalAll() 唤醒t1和t2线程，t5发出c2.signal()唤醒t3线程。

ReentrantReadWriteLock

读写分离锁，读读共享、写写互斥、读写互斥。

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();
    }
}

解释：t1和t2都是读，是共享的，可同时获得readLock同时进入read方法执行。t1是读和t3是写，是互斥的，只有t1执行完t3才能执行。t3、t4都是写，是互斥的，只有等t3执行完t4才能继续。