读写锁
ReadWriteLock
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
/**
* 独占锁(写锁)一次只能被一个线程占有
* 共享锁(读锁)多个线程可以同时占有
* ReadWriteLock
* 读-读 可以共存
* 读-写 不能共存
* 写-写 必能共存
*/
public class ReadWriteLockDemo {
public static void main(String[] args) {
// MyCache myCache = new MyCache();
MyCacheLock myCache = new MyCacheLock();
// 写入
for (int i = 1; i <= 5; i++) {
// lambda 表达式无法访问到外部的变量,我们只能通过final变量来进行一个中间转换
final int temp = i;
new Thread(()->{
myCache.put(temp+"",temp+"");
},String.valueOf(i)).start();
}
for (int i = 1; i <= 5; i++) {
final int temp = i;
new Thread(()->{
myCache.get(temp+"");
},String.valueOf(i)).start();
}
}
}
// 加锁的
class MyCacheLock {
// volatile 写入缓存时会有锁总线程的操作,不可能在写入的过程中间被读取
private volatile Map<String,Object> map = new HashMap<>();
// private Lock lock = new ReentrantLock();
// 使用读写锁:更加细粒度的控制
private ReadWriteLock readWriteLock = new ReentrantReadWriteLock();
//存,写入的时候,只希望同时有一个线程写
public void put(String key,Object value) {
// lock.lock();
readWriteLock.writeLock().lock();
try {
System.out.println(Thread.currentThread().getName()+"写入"+key);
map.put(key,value);
System.out.println(Thread.currentThread().getName()+"写入OK");
} catch (Exception e) {
e.printStackTrace();
} finally {
readWriteLock.writeLock().unlock();
}
}
//取,读的时候所有人都可以读
public void get(String key) {
readWriteLock.readLock().lock();
try {
System.out.println(Thread.currentThread().getName()+"读取"+key);
Object o = map.get(key);
System.out.println(Thread.currentThread().getName()+"读取OK");
} catch (Exception e) {
e.printStackTrace();
} finally {
readWriteLock.readLock().unlock();
}
}
}
/**
* 自定义缓存
*/
class MyCache {
// volatile 写入缓存时会有锁总线程的操作,不可能在写入的过程中间被读取
private volatile Map<String,Object> map = new HashMap<>();
//存,写
public void put(String key,Object value) {
System.out.println(Thread.currentThread().getName()+"写入"+key);
map.put(key,value);
System.out.println(Thread.currentThread().getName()+"写入OK");
}
//取
public void get(String key) {
System.out.println(Thread.currentThread().getName()+"读取"+key);
Object o = map.get(key);
System.out.println(Thread.currentThread().getName()+"读取OK");
}
}
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