12-Java5读写锁技术的妙用
只要有写就要互斥，否则就要有问题，如果都是读那么就没问题
都是读就不要锁了，否则影响性能
package cn.itcast.demo.thread;
import java.util.Random;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
public class ReadAndWriteLock {
public static void main(String[] args) {
final BusinessService businessService = new BusinessService();
for (int i=0; i<3; i++) {
// 读
new Thread(new Runnable() {
@Override
public void run() {
while (true) {
businessService.get();
}
}
}).start();
// 写
new Thread(new Runnable() {
@Override
public void run() {
while (true) {
int data = new Random().nextInt(10000);
businessService.put(data);
}
}
}).start();
}
}
}
class BusinessService {
private Object data;
ReadWriteLock rwLock = new ReentrantReadWriteLock();
// 读
public void get() {
rwLock.readLock().lock();
try {
System.out.println("==========================================" +
Thread.currentThread().getName() + " is ready to read data...");
Thread.sleep(1000);
System.out.println(Thread.currentThread().getName() + " has red data: " + this.data);
} catch (Exception e) {
e.printStackTrace();
} finally {
rwLock.readLock().unlock();
}
}
// 写
public void put(Object data) {
rwLock.writeLock().lock();
try {
System.out.println(Thread.currentThread().getName() + " is ready to 【write】...");
Thread.sleep(1000);
this.data = data;
System.out.println(Thread.currentThread().getName() + " has 【wrote】 data: " + this.data);
} catch (Exception e) {
e.printStackTrace();
} finally {
rwLock.writeLock().unlock();
}
}
}
打印结果：
==========================================Thread-0 is ready to read data... ==========================================Thread-2 is ready to read data... ==========================================Thread-4 is ready to read data... Thread-0 has red data: null Thread-4 has red data: null Thread-2 has red data: null Thread-3 is ready to 【write】... Thread-3 has 【wrote】 data: 7204 Thread-3 is ready to 【write】... Thread-3 has 【wrote】 data: 3655 Thread-3 is ready to 【write】... Thread-3 has 【wrote】 data: 5606 Thread-3 is ready to 【write】... Thread-3 has 【wrote】 data: 975 Thread-3 is ready to 【write】... Thread-3 has 【wrote】 data: 9057 Thread-3 is ready to 【write】... Thread-3 has 【wrote】 data: 2011 Thread-3 is ready to 【write】... Thread-3 has 【wrote】 data: 2788 Thread-3 is ready to 【write】... Thread-3 has 【wrote】 data: 2383 Thread-5 is ready to 【write】... Thread-5 has 【wrote】 data: 819 Thread-1 is ready to 【write】... Thread-1 has 【wrote】 data: 1529 Thread-1 is ready to 【write】... Thread-1 has 【wrote】 data: 3665 Thread-1 is ready to 【write】... Thread-1 has 【wrote】 data: 252 ==========================================Thread-0 is ready to read data... ==========================================Thread-4 is ready to read data... ==========================================Thread-2 is ready to read data... Thread-4 has red data: 252 Thread-0 has red data: 252 Thread-2 has red data: 252 Thread-3 is ready to 【write】... Thread-3 has 【wrote】 data: 6139 Thread-3 is ready to 【write】... Thread-3 has 【wrote】 data: 6386 Thread-3 is ready to 【write】... Thread-3 has 【wrote】 data: 9229 Thread-3 is ready to 【write】... Thread-3 has 【wrote】 data: 9532 Thread-3 is ready to 【write】... Thread-3 has 【wrote】 data: 6713 Thread-3 is ready to 【write】... Thread-3 has 【wrote】 data: 7474 Thread-3 is ready to 【write】... Thread-3 has 【wrote】 data: 8841 Thread-3 is ready to 【write】... Thread-3 has 【wrote】 data: 1590 Thread-5 is ready to 【write】... Thread-5 has 【wrote】 data: 3066 Thread-1 is ready to 【write】... Thread-1 has 【wrote】 data: 2454 ==========================================Thread-4 is ready to read data... ==========================================Thread-0 is ready to read data... ==========================================Thread-2 is ready to read data... Thread-2 has red data: 2454 Thread-0 has red data: 2454 Thread-4 has red data: 2454 Thread-3 is ready to 【write】... Thread-3 has 【wrote】 data: 4301 Thread-3 is ready to 【write】... Thread-3 has 【wrote】 data: 6942 Thread-3 is ready to 【write】... Thread-3 has 【wrote】 data: 3463 Thread-3 is ready to 【write】... Thread-3 has 【wrote】 data: 4326 Thread-3 is ready to 【write】... Thread-3 has 【wrote】 data: 127 Thread-3 is ready to 【write】... Thread-3 has 【wrote】 data: 3896 Thread-3 is ready to 【write】... Thread-3 has 【wrote】 data: 7426 Thread-3 is ready to 【write】... Thread-3 has 【wrote】 data: 9235 Thread-5 is ready to 【write】... Thread-5 has 【wrote】 data: 1826 Thread-5 is ready to 【write】... Thread-5 has 【wrote】 data: 512 Thread-5 is ready to 【write】... Thread-5 has 【wrote】 data: 9695 Thread-1 is ready to 【write】... Thread-1 has 【wrote】 data: 5217 Thread-1 is ready to 【write】... Thread-1 has 【wrote】 data: 4643 Thread-1 is ready to 【write】... Thread-1 has 【wrote】 data: 6613 Thread-1 is ready to 【write】... Thread-1 has 【wrote】 data: 7693 Thread-1 is ready to 【write】... Thread-1 has 【wrote】 data: 3476 Thread-1 is ready to 【write】... Thread-1 has 【wrote】 data: 8197 ==========================================Thread-0 is ready to read data... ==========================================Thread-4 is ready to read data... ==========================================Thread-2 is ready to read data... Thread-2 has red data: 8197 Thread-4 has red data: 8197 Thread-0 has red data: 8197 Thread-3 is ready to 【write】... Thread-3 has 【wrote】 data: 4247 Thread-3 is ready to 【write】... Thread-3 has 【wrote】 data: 3827 Thread-5 is ready to 【write】... Thread-5 has 【wrote】 data: 1665 Thread-5 is ready to 【write】... Thread-5 has 【wrote】 data: 5349 Thread-5 is ready to 【write】...
写一个缓存系统的Demo
package cn.itcast.demo.thread;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
public class CacheDemo {
public static void main(String[] args) {
CacheService cacheService = new CacheService();
Object value = cacheService.getData("hello");
System.out.println(value);
}
}
class CacheService {
private Map<String, Object> cache = new HashMap<String, Object>();
private ReadWriteLock rwLock = new ReentrantReadWriteLock();
public Object getData(String key) {
rwLock.readLock().lock();
Object value = null;
try {
value = cache.get(key);
// 多线程并发访问的时候，如果任何一个线程发现数据为空，就不让其他线程再进行读写操作
if (value == null) {
// 不让其他线程读
rwLock.readLock().unlock();
// 同时开启写锁
rwLock.writeLock().lock();
try {
if (value == null) { // 第一个线程进来发现是空，就进行写操作，以后的线程进来发现数据不为空就不进行写操作
System.out.println("查数据库...");
value = "aaaa"; // 实际去查询数据库
}
} catch (Exception e) {
e.printStackTrace();
} finally {
// 关闭写锁
rwLock.writeLock().unlock();
}
// 重新开启读锁
rwLock.readLock().lock();
}
} catch (Exception e) {
e.printStackTrace();
} finally {
rwLock.readLock().unlock();
}
return value;
}
}
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