yaclty/Java-Interview-Guide
1
0
Fork 0
mirror of https://github.com/Snailclimb/JavaGuide synced 2025-06-25 02:27:10 +08:00
Code Issues Projects Releases Wiki Activity

[docs update]完善对synchronized关键字的介绍

Browse Source
This commit is contained in:
guide 2022-01-24 09:44:46 +08:00
parent b40c4ebd88
commit 58cf4d48eb
5 changed files with 16 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
docs/java/concurrent/images/interview-questions/synchronized-get-lock-code-block.drawio Normal file
View File

@ -0,0 +1 @@
<mxfile host="Electron" modified="2022-01-24T01:30:38.715Z" agent="5.0 (Macintosh; Intel Mac OS X 10_16_0) AppleWebKit/537.36 (KHTML, like Gecko) draw.io/13.4.5 Chrome/83.0.4103.122 Electron/9.1.0 Safari/537.36" etag="l1tJc7jft47xw4GR_2dM" version="13.4.5" type="device"><diagram id="f1uOqe90rjhexKzs8PuL" name="Page-1">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</diagram></mxfile>

BIN
docs/java/concurrent/images/interview-questions/synchronized-get-lock-code-block.png Normal file
View File

Binary file not shown.
Side by Side

After

Width:  |  Height:  |  Size: 44 KiB

1
docs/java/concurrent/images/interview-questions/synchronized-release-lock-block.drawio Normal file
View File

@ -0,0 +1 @@
<mxfile host="Electron" modified="2022-01-24T01:31:02.213Z" agent="5.0 (Macintosh; Intel Mac OS X 10_16_0) AppleWebKit/537.36 (KHTML, like Gecko) draw.io/13.4.5 Chrome/83.0.4103.122 Electron/9.1.0 Safari/537.36" etag="tG8e46NqnXu62oEqxvIZ" version="13.4.5" type="device"><diagram id="l-JW3fph1e97gRfsgveQ" name="Page-1">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</diagram></mxfile>

BIN
docs/java/concurrent/images/interview-questions/synchronized-release-lock-block.png Normal file
View File

Binary file not shown.
Side by Side

After

Width:  |  Height:  |  Size: 160 KiB

18
docs/java/concurrent/java并发进阶常见面试题总结.md
View File

@ -125,9 +125,7 @@ public class SynchronizedDemo {
![synchronized关键字原理](https://my-blog-to-use.oss-cn-beijing.aliyuncs.com/2019-6/synchronized关键字原理.png)
从上面我们可以看出：
**`synchronized` 同步语句块的实现使用的是 `monitorenter` 和 `monitorexit` 指令，其中 `monitorenter` 指令指向同步代码块的开始位置，`monitorexit` 指令则指明同步代码块的结束位置。**
从上面我们可以看出：**`synchronized` 同步语句块的实现使用的是 `monitorenter` 和 `monitorexit` 指令，其中 `monitorenter` 指令指向同步代码块的开始位置，`monitorexit` 指令则指明同步代码块的结束位置。**
当执行 `monitorenter` 指令时，线程试图获取锁也就是获取 **对象监视器 `monitor`** 的持有权。
@ -137,7 +135,15 @@ public class SynchronizedDemo {
在执行`monitorenter`时，会尝试获取对象的锁，如果锁的计数器为 0 则表示锁可以被获取，获取后将锁计数器设为 1 也就是加 1。
在执行 `monitorexit` 指令后，将锁计数器设为 0，表明锁被释放。如果获取对象锁失败，那当前线程就要阻塞等待，直到锁被另外一个线程释放为止。
![执行 monitorenter 获取锁](./images/interview-questions/synchronized-get-lock-code-block.png)
对象锁的的拥有者线程才可以执行 `monitorexit` 指令来释放锁。在执行 `monitorexit` 指令后，将锁计数器设为 0，表明锁被释放，其他线程可以尝试获取锁。
![执行 monitorexit 释放锁](./images/interview-questions/synchronized-release-lock-block.png)
如果获取对象锁失败，那当前线程就要阻塞等待，直到锁被另外一个线程释放为止。
#### 1.3.2. synchronized 修饰方法的的情况
@ -154,6 +160,8 @@ public class SynchronizedDemo2 {
`synchronized` 修饰的方法并没有 `monitorenter` 指令和 `monitorexit` 指令，取得代之的确实是 `ACC_SYNCHRONIZED` 标识，该标识指明了该方法是一个同步方法。JVM 通过该 `ACC_SYNCHRONIZED` 访问标志来辨别一个方法是否声明为同步方法，从而执行相应的同步调用。
如果是实例方法，JVM 会尝试获取实例对象的锁。如果是静态方法，JVM 会尝试获取当前 class 的锁。
#### 1.3.3.总结
`synchronized` 同步语句块的实现使用的是 `monitorenter` 和 `monitorexit` 指令，其中 `monitorenter` 指令指向同步代码块的开始位置，`monitorexit` 指令则指明同步代码块的结束位置。
@ -164,6 +172,8 @@ public class SynchronizedDemo2 {
相关推荐：[Java锁与线程的那些事 - 有赞技术团队](https://tech.youzan.com/javasuo-yu-xian-cheng-de-na-xie-shi/) 。
🧗🏻进阶一下：学有余力的小伙伴可以抽时间详细研究一下对象监视器 `monitor`。
### 1.4. 说说 JDK1.6 之后的 synchronized 关键字底层做了哪些优化，可以详细介绍一下这些优化吗
JDK1.6 对锁的实现引入了大量的优化，如偏向锁、轻量级锁、自旋锁、适应性自旋锁、锁消除、锁粗化等技术来减少锁操作的开销。