Java 中的锁 ReentrantLock
Java juc 锁 About 1,757 words特性
可重入、互斥(读写互斥、写写互斥、读读互斥),只能有一个线程进行操作。
默认是非公平锁,可通过构造函数指定是否是公平锁。非公平锁性能略微好一些,主要是第一个持有锁的线程解锁后,若AQS
的双向链表中有等待抢锁的线程时,不从双向链表中取,而是直接给新来的抢锁线程获得。
代码示例
public class ReentrantLockDemo {
static Lock lock = new ReentrantLock();
public static void main(String[] args) {
new Thread(() -> {
lock.lock();
// 加几次放几次
lock.lock();
try {
System.out.println(LocalDateTime.now() + " " + Thread.currentThread().getName() + "----------外层");
lock.lock();
try {
System.out.println(LocalDateTime.now() + " " + Thread.currentThread().getName() + "---------内层");
} finally {
lock.unlock();
}
} finally {
try {
TimeUnit.SECONDS.sleep(3);
} catch (InterruptedException e) {
e.printStackTrace();
}
lock.unlock();
lock.unlock();
}
}, "t1").start();
new Thread(() -> {
lock.lock();
try {
System.out.println(LocalDateTime.now() + " " + Thread.currentThread().getName() + "----------外层");
lock.lock();
try {
System.out.println(LocalDateTime.now() + " " + Thread.currentThread().getName() + "---------内层");
} finally {
lock.unlock();
}
} finally {
lock.unlock();
}
}, "t2").start();
}
}
输出:
2021-03-27T20:24:26.263 t1----------外层
2021-03-27T20:24:26.263 t1---------内层
2021-03-27T20:24:29.267 t2----------外层
2021-03-27T20:24:29.268 t2---------内层
Views: 1,814 · Posted: 2021-04-07
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