多把锁
一间大屋子有两个功能:睡觉、学习,互不相干。现在小南要学习,小女要睡觉,但如果只用一间屋子(一个对象锁)的话,那么并发度很低. 解决方法是准备多个房间(多个对象锁)
@Slf4j(topic = "c.test27:")
public class Test27 {
public static void main(String[] args) {
BigRoom bigRoom = new BigRoom();
new Thread(() -> {
try {
bigRoom.study();
} catch (InterruptedException e) {
e.printStackTrace();
}
}, "小南").start();
new Thread(() -> {
try {
bigRoom.sleep();
} catch (InterruptedException e) {
e.printStackTrace();
}
}, "小女").start();
}
}
//共享资源
class BigRoom {
public void sleep() throws InterruptedException {
synchronized (this) {
log.debug("sleeping 2 小时");
TimeUnit.SECONDS.sleep(2);
}
}
public void study() throws InterruptedException {
synchronized (this) {
log.debug("study 1 小时");
TimeUnit.SECONDS.sleep(1);
}
}
}
改进后
- 将锁的粒度细分
- 好处,是可以增强并发度
- 坏处,如果一个线程需要同时获得多把锁,就容易发生死锁
class BigRoom {
private final Object studyRoom = new Object();
private final Object bedRoom = new Object();
public void sleep() throws InterruptedException {
synchronized (bedRoom) {
log.debug("sleeping 2 小时");
TimeUnit.SECONDS.sleep(2);
}
}
public void study() throws InterruptedException {
synchronized (studyRoom) {
log.debug("study 1 小时");
TimeUnit.SECONDS.sleep(1);
}
}
}