使用synchronized实现一个Lock代码详解
刚看到这个题目的时候无从下手，因为觉得synchronized和lock在加锁的方式上有很大不同，比如，看看正常情况下synchronized时如何加锁的。
方式一：
public synchronized void a(){
//TODO
}
方式二：
public void b(){
synchronized(this){
//TODO
}
}
从这两种方式来看，锁都是加在｛｝之间的，我们再来看看Lock是如何做的呢:
public void c() {
lock.lock();
try {
// TODO
} finally {
lock.unlock();
}
}
这种方式的锁是加在lock()和unlock()之间的，所以要想实现一个lock功能，就要想怎么实现这样两个方法，lock()和unlock()方法，先定义一个框架如下所示：
public void lock(){
}
public void unlock(){
}
然后要想怎么用synchronized去实现这两个方法。
现在其实只是稍微清楚了一点思路，但是还不知道怎么去填充这两个方法，这是后再来分析一下Lock的加锁有什么特点，再来看看这段代码：
public void c() {
lock.lock();
//When current thread get the lock, other thread has to wait
try {
//current thread get in the lock, other thread can not get in
// TODO
}
finally {
lock.unlock();
//current thread release the lock
}
}
这段代码我只是加了一点注释，别的什么都没有做，是不是帮助理解这段代码，看看出现频率最高的词是什么，是currentthread，那么我们去填充lock()和unlock()方法的时候是不是注意要抓住currentthread这个关键字就可以找到解决方案呢？答案是肯定的。
接着分析，使用synchronized的时候如何让线程等待呢？是用wait()方法。怎么让线程唤醒呢，是用notify()方法。那么就要在lock()方法中使用wait()方法，在unlock()方法中使用notify()方法。那么我们在使用wait()和notify()的时候是有一个条件的，想想我们应该使用什么作为条件呢？
我们应该使用当前锁是否被占用作为判断条件，如果锁被占用，currentthread等待，想想我们在使用synchronized的时候是不是一直使用的这个条件，答案也是肯定的。
再来分析一下什么时候释放锁，使用什么作为条件，想想如果线程A拿到了锁，线程B能释放吗？当然不能，如果B能释放就违反了原则，当然不能。肯定是A线程的锁只能A来释放。所以判断条件就是判断持有锁的线程是不是currentthread，如果是的话，可以释放，不是的话当然不能。
现在来看看完整的代码：
package test.lock;
import java.util.Random;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadFactory;
public class NaiveLock {
private static final long NONE = -1;
private long owner = NONE;
private Boolean isLooked() {
return owner != NONE;
}
public synchronized void lock() {
long currentThreadId = Thread.currentThread().getId();
if (owner == currentThreadId) {
throw new IllegalStateException("Lock has been acquired by current thread");
}
while (this.isLooked()) {
System.out.println(String.format("thread %s is waitting lock", currentThreadId));
try {
wait();
}
catch (InterruptedException e) {
e.printStackTrace();
}
}
owner = currentThreadId;
System.out.println(String.format("Lock is acquired by thread %s", owner));
}
public synchronized void unlock() {
if (!this.isLooked() || owner != Thread.currentThread().getId()) {
throw new IllegalStateException("Only Lock owner can unlock the lock");
}
System.out.println(String.format("thread %s is unlocking", owner));
System.out.println();
owner = NONE;
notify();
}
public static void main(String[] args) {
final NaiveLock lock = new NaiveLock();
ExecutorService executor = Executors.newFixedThreadPool(20, new ThreadFactory() {
private ThreadGroup group = new ThreadGroup("test thread group");
{
group.setDaemon(true);
}
@Override
public Thread newThread(Runnable r) {
return new Thread(group, r);
}
}
);
for (int i = 0; i < 20; i++) {
executor.submit(new Runnable() {
@Override
public void run() {
lock.lock();
System.out.println(String.format("thread %s is running...", Thread.currentThread().getId()));
try {
Thread.sleep(new Random().nextint(1000));
}
catch (InterruptedException e) {
e.printStackTrace();
}
lock.unlock();
}
}
);
}
}
}
运行一下看看结果：
Lock is acquired by thread 8 thread 8 is running... thread 27 is waitting lock thread 26 is waitting lock thread 25 is waitting lock thread 24 is waitting lock thread 23 is waitting lock thread 22 is waitting lock thread 21 is waitting lock thread 20 is waitting lock thread 19 is waitting lock thread 18 is waitting lock thread 17 is waitting lock thread 16 is waitting lock thread 15 is waitting lock thread 14 is waitting lock thread 13 is waitting lock thread 12 is waitting lock thread 11 is waitting lock thread 10 is waitting lock thread 9 is waitting lock thread 8 is unlocking Lock is acquired by thread 27 thread 27 is running... thread 27 is unlocking Lock is acquired by thread 26 thread 26 is running... thread 26 is unlocking Lock is acquired by thread 25 thread 25 is running... thread 25 is unlocking Lock is acquired by thread 24 thread 24 is running... thread 24 is unlocking Lock is acquired by thread 23 thread 23 is running... thread 23 is unlocking Lock is acquired by thread 22 thread 22 is running... thread 22 is unlocking Lock is acquired by thread 21 thread 21 is running... thread 21 is unlocking Lock is acquired by thread 20 thread 20 is running... thread 20 is unlocking Lock is acquired by thread 19 thread 19 is running... thread 19 is unlocking Lock is acquired by thread 18 thread 18 is running... thread 18 is unlocking Lock is acquired by thread 17 thread 17 is running... thread 17 is unlocking Lock is acquired by thread 16 thread 16 is running... thread 16 is unlocking Lock is acquired by thread 15 thread 15 is running... thread 15 is unlocking Lock is acquired by thread 14 thread 14 is running... thread 14 is unlocking Lock is acquired by thread 13 thread 13 is running... thread 13 is unlocking Lock is acquired by thread 12 thread 12 is running... thread 12 is unlocking Lock is acquired by thread 11 thread 11 is running... thread 11 is unlocking Lock is acquired by thread 10 thread 10 is running... thread 10 is unlocking Lock is acquired by thread 9 thread 9 is running... thread 9 is unlocking
如果把for循环改成30次，再看一下结果：
Lock is acquired by thread 8 thread 8 is running... thread 27 is waitting lock thread 26 is waitting lock thread 25 is waitting lock thread 24 is waitting lock thread 23 is waitting lock thread 22 is waitting lock thread 21 is waitting lock thread 20 is waitting lock thread 19 is waitting lock thread 18 is waitting lock thread 17 is waitting lock thread 16 is waitting lock thread 15 is waitting lock thread 14 is waitting lock thread 13 is waitting lock thread 12 is waitting lock thread 11 is waitting lock thread 10 is waitting lock thread 9 is waitting lock thread 8 is unlocking Lock is acquired by thread 27 thread 27 is running... thread 8 is waitting lock thread 27 is unlocking Lock is acquired by thread 27 thread 27 is running... thread 26 is waitting lock thread 27 is unlocking Lock is acquired by thread 27 thread 27 is running... thread 25 is waitting lock thread 27 is unlocking Lock is acquired by thread 24 thread 24 is running... thread 27 is waitting lock thread 24 is unlocking Lock is acquired by thread 23 thread 23 is running... thread 24 is waitting lock thread 23 is unlocking Lock is acquired by thread 22 thread 22 is running... thread 23 is waitting lock thread 22 is unlocking Lock is acquired by thread 22 thread 22 is running... thread 21 is waitting lock thread 22 is unlocking Lock is acquired by thread 22 thread 22 is running... thread 20 is waitting lock thread 22 is unlocking Lock is acquired by thread 22 thread 22 is running... thread 19 is waitting lock thread 22 is unlocking Lock is acquired by thread 22 thread 22 is running... thread 18 is waitting lock thread 22 is unlocking Lock is acquired by thread 17 thread 17 is running... thread 17 is unlocking Lock is acquired by thread 16 thread 16 is running... thread 16 is unlocking Lock is acquired by thread 15 thread 15 is running... thread 15 is unlocking Lock is acquired by thread 14 thread 14 is running... thread 14 is unlocking Lock is acquired by thread 13 thread 13 is running... thread 13 is unlocking Lock is acquired by thread 12 thread 12 is running... thread 12 is unlocking Lock is acquired by thread 11 thread 11 is running... thread 11 is unlocking Lock is acquired by thread 10 thread 10 is running... thread 10 is unlocking Lock is acquired by thread 9 thread 9 is running... thread 9 is unlocking Lock is acquired by thread 8 thread 8 is running... thread 8 is unlocking Lock is acquired by thread 26 thread 26 is running... thread 26 is unlocking Lock is acquired by thread 25 thread 25 is running... thread 25 is unlocking Lock is acquired by thread 27 thread 27 is running... thread 27 is unlocking Lock is acquired by thread 24 thread 24 is running... thread 24 is unlocking Lock is acquired by thread 23 thread 23 is running... thread 23 is unlocking Lock is acquired by thread 21 thread 21 is running... thread 21 is unlocking Lock is acquired by thread 20 thread 20 is running... thread 20 is unlocking Lock is acquired by thread 19 thread 19 is running... thread 19 is unlocking Lock is acquired by thread 18 thread 18 is running... thread 18 is unlocking
总结
以上就是本文关于使用synchronized实现一个Lock代码详解的全部内容，希望对大家有所帮助。感兴趣的朋友可以继续参阅本站：
Java线程同步Lock同步锁代码示例
Java编程synchronized与lock的区别【推荐】
Java多线程之readwritelock读写分离的实现代码
如有不足之处，欢迎留言指出。感谢朋友们对本站的支持！
-
本文向大家介绍java-synchronized 嵌套使用代码详解，包括了java-synchronized 嵌套使用代码详解的使用技巧和注意事项，需要的朋友参考一下 当synchronized使用过多时，可能会造成死锁，那么死锁到底是怎么一回事呢。先看下面的代码，实现死锁： 以上代码由于 synchronized 的同步造成了死锁，死锁是两个或多个线程同时等待对方的完成，而程序无法继续执行。在解
-
本文向大家介绍详谈Lock与synchronized 的区别，包括了详谈Lock与synchronized 的区别的使用技巧和注意事项，需要的朋友参考一下 1、lock是可中断锁，而synchronized 不是可中断锁 线程A和B都要获取对象O的锁定，假设A获取了对象O锁，B将等待A释放对O的锁定， 如果使用 synchronized ，如果A不释放，B将一直等下去，不能被中断 如果 使用Ree
-
本文向大家介绍详解spring中使用solr的代码实现，包括了详解spring中使用solr的代码实现的使用技巧和注意事项，需要的朋友参考一下 在介绍solr的使用方法之前，我们需要安装solr的服务端集群。基本上就是安装zookeeper,tomcat,jdk,solr，然后按照需要配置三者的配置文件即可。由于本人并没有具体操作过如何进行solr集群的搭建。所以关于如何搭建solr集群，读者可以
-
本文向大家介绍通过实例解析synchronized和lock区别，包括了通过实例解析synchronized和lock区别的使用技巧和注意事项，需要的朋友参考一下 1，原始构成 synchronized是关键字，属于JVM层面，通过wait，notify和notifyAll来调度线程。 Lock是具体类，是api层面的锁。 2，使用方法 synchronized不需要用户手动去释放锁， 当sync
-
本文向大家介绍JS 实现计算器详解及实例代码（一），包括了JS 实现计算器详解及实例代码（一）的使用技巧和注意事项，需要的朋友参考一下 Javascript 实现计算器： 系列文章： JS 实现计算器详解及实例代码（一） Javascript 实现计算器时间功能详解及实例（二） 小型JavaScript计算器 自己寻思出的解决方案，比较笨拙的方法，虽然完成了但是还有不少bug，用的方法也不是最有效
-
本文向大家介绍浅谈Synchronized和Lock的区别，包括了浅谈Synchronized和Lock的区别的使用技巧和注意事项，需要的朋友参考一下 如下所示： Synchronized是内置的java关键字，Lock是一个java类。 Synchronized无法判断是否获取到了锁，Lock可以判断是否获取到了锁。 Synchronized会自动释放锁，Lock必须手动释放锁。 Synchro