ReentrantReadWriteLock類為讀寫鎖。 讀寫鎖也有兩個(gè)鎖，一個(gè)是讀操作相關(guān)的鎖，稱為共享鎖； 另一個(gè)是寫操作相關(guān)的鎖，也叫排他鎖。 也就是多個(gè)讀鎖之間不互斥，讀鎖與寫鎖互斥，寫鎖與寫鎖互斥。

一個(gè)線程擁有了對(duì)象A的寫鎖，在釋放寫鎖前其他線程無(wú)法獲得A的讀鎖、寫鎖，因此其他線程此時(shí)無(wú)法讀寫；
一個(gè)線程擁有了對(duì)象A的讀鎖，在釋放前其他線程可以獲得A的讀鎖但無(wú)法獲得A的寫鎖，因此其他線程此時(shí)可以讀不可以寫。
不加讀鎖的話其他線程是可以讀，但也可以寫，這時(shí)就可能導(dǎo)致數(shù)據(jù)不一致了

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讀鎖共享

? ?使用lock.readLock()讀鎖可以提高程序運(yùn)行效率，允許多個(gè)線程同時(shí)執(zhí)行l(wèi)ock()方法后面的代碼

import java.util.concurrent.locks.ReentrantReadWriteLock;public class Service {private ReentrantReadWriteLock lock = new ReentrantReadWriteLock();public void read(){try {lock.readLock().lock();System.out.println("獲得讀鎖"+Thread.currentThread().getName()+" "+System.currentTimeMillis());Thread.sleep(10000);} catch (InterruptedException e) {e.printStackTrace();}finally {lock.readLock().unlock();}} }public class ThreadA extends Thread{private Service service = new Service();public ThreadA(Service service){super();this.service = service;}@Overridepublic void run(){service.read();} }public class ThreadB extends Thread{private Service service = new Service();public ThreadB(Service service){super();this.service = service;}@Overridepublic void run(){service.read();} }public class Run {public static void main(String[] args) {Service service = new Service();ThreadA a = new ThreadA(service);ThreadB b = new ThreadB(service);a.setName("A");b.setName("B");a.start();b.start();} }

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寫鎖互斥

? 使用寫鎖代碼lock.writeLock()的效果就是同一時(shí)間只允許一個(gè)線程執(zhí)行l(wèi)ock()方法后面的代碼

import java.util.concurrent.locks.ReentrantReadWriteLock;public class Service {private ReentrantReadWriteLock lock = new ReentrantReadWriteLock();public void writeLock(){try {lock.writeLock().lock();System.out.println("進(jìn)入寫鎖:"+Thread.currentThread().getName()+" 時(shí)間:"+System.currentTimeMillis());Thread.sleep(10000);} catch (InterruptedException e) {e.printStackTrace();}finally{lock.writeLock().unlock();}} }public class ThreadA extends Thread{private Service service;public ThreadA(Service service){super();this.service = service;}@Overridepublic void run(){service.writeLock();} }public class ThreadB extends Thread{private Service service;public ThreadB(Service service){super();this.service = service;}@Overridepublic void run(){service.writeLock();} }public class Run {public static void main(String[] args){Service s = new Service();ThreadA a = new ThreadA(s);ThreadB b = new ThreadB(s);a.setName("A");b.setName("B");a.start();b.start();} }

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