# juc-study
**Repository Path**: ilovemo/juc-study
## Basic Information
- **Project Name**: juc-study
- **Description**: juc高并发编程学习代码
- **Primary Language**: Java
- **License**: GPL-2.0
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No
## Statistics
- **Stars**: 1
- **Forks**: 0
- **Created**: 2020-05-16
- **Last Updated**: 2020-12-19
## Categories & Tags
**Categories**: Uncategorized
**Tags**: None
## README
# 多线程进阶---JUC并发编程
## 1.Lock锁（重点）
> 传统 Synchronizd
```java
package com.godfrey.demo01;
/**
* description : 模拟卖票
*
* @author godfrey
* @since 2020-05-14
*/
public class SaleTicketDemo01 {
public static void main(String[] args) {
Ticket ticket = new Ticket();
new Thread(() -> {
for (int i = 0; i < 60; i++) {
ticket.sale();
}
}, "A").start();
new Thread(() -> {
for (int i = 0; i < 60; i++) {
ticket.sale();
}
}, "B").start();
new Thread(() -> {
for (int i = 0; i < 60; i++) {
ticket.sale();
}
}, "C").start();
}
}
//资源类OOP
class Ticket {
private int number = 50;
public synchronized void sale() {
if (number > 0) {
System.out.println(Thread.currentThread().getName() + "卖出了第" + (50 - (--number)) + "票，剩余：" + number);
}
}
}
```
> Synchronized(本质：队列+锁)和Lock区别
1. Synchronized 是内置关键字，Lock 是一个Java类
2. Synchronized 无法判断锁的状态，Lock 可以判断是否获取到了锁
3. Synchronized 会自动释放锁，Lock 必须手动释放！如果不释放锁，**死锁**
4. Synchronized 线程1（获得锁，阻塞）、线程2（等待，傻傻的等）；Lock 锁就不一定会等待下去（tryLock）
5. Synchronized 可重入锁，不可中断，非公平；Lock 可重入锁 ，可以判断锁，非公平（可以自己设置）；
6. Synchronized 适合锁少量的代码同步问题，Lock 适合锁大量的同步代码！
> 锁是什么，如何判断锁的是谁
## 2.线程之间通信问题：生成者消费者问题
> Synchronized版生产者消费者问题
```java
package proc;
/**
* description : 生产者消费者问题
*
* @author godfrey
* @since 2020-05-14
*/
public class A {
public static void main(String[] args) {
Data data = new Data();
new Thread(() -> {
for (int i = 0; i < 10; i++) {
try {
data.increment();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, "A").start();
new Thread(() -> {
for (int i = 0; i < 10; i++) {
try {
data.decrement();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, "B").start();
}
}
// 判断等待，业务，通知
class Data {
private int number = 0;
//+1
public synchronized void increment() throws InterruptedException {
if (number != 0) {
//等待
this.wait();
}
number++;
System.out.println(Thread.currentThread().getName() + "==>" + number);
//通知其他线程，我+1完毕了
this.notifyAll();
}
//-1
public synchronized void decrement() throws InterruptedException {
if (number == 0) {
//等待
this.wait();
}
number--;
System.out.println(Thread.currentThread().getName() + "==>" + number);
//通知其他线程，我-1完毕了
this.notifyAll();
}
}
```
> Lock接口
公平锁：十分公平：可以先来后到
**非公平锁：十分不公平：可以插队 （默认）**
```java
package com.godfrey.demo01;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* description : 模拟卖票
*
* @author godfrey
* @since 2020-05-14
*/
public class SaleTicketDemo02 {
public static void main(String[] args) {
Ticket ticket = new Ticket();
new Thread(() -> { for (int i = 0; i < 40; i++) ticket.sale(); }, "A").start();
new Thread(() -> { for (int i = 0; i < 40; i++) ticket.sale(); }, "B").start();
new Thread(() -> { for (int i = 0; i < 40; i++) ticket.sale(); }, "C").start();
}
}
//Lock
class Ticket2 {
private int number = 30;
Lock lock = new ReentrantLock();
public synchronized void sale() {
lock.lock();
try {
if (number > 0) {
System.out.println(Thread.currentThread().getName() + "卖出了第" + (50 - (number--)) + "票，剩余：" + number);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
}
```
> 问题存在，ABCD四个线程！怎么解决？
if ==>while
```java
package com.godfrey.proc;
/**
* description : Synchronized版生成者消费者问题
*
* @author godfrey
* @since 2020-05-14
*/
public class A {
public static void main(String[] args) {
Data data = new Data();
new Thread(() -> {
for (int i = 0; i < 10; i++) {
try {
data.increment();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, "A").start();
new Thread(() -> {
for (int i = 0; i < 10; i++) {
try {
data.increment();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, "B").start();
new Thread(() -> {
for (int i = 0; i < 10; i++) {
try {
data.decrement();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, "C").start();
new Thread(() -> {
for (int i = 0; i < 10; i++) {
try {
data.decrement();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, "D").start();
}
}
// 判断等待，业务，通知
class Data {
private int number = 0;
//+1
public synchronized void increment() throws InterruptedException {
while (number != 0) {
//等待
this.wait();
}
number++;
System.out.println(Thread.currentThread().getName() + "==>" + number);
//通知其他线程，我+1完毕了
this.notifyAll();
}
//-1
public synchronized void decrement() throws InterruptedException {
while (number == 0) {
//等待
this.wait();
}
number--;
System.out.println(Thread.currentThread().getName() + "==>" + number);
//通知其他线程，我-1完毕了
this.notifyAll();
}
}
```
> JUC版的生产者和消费者问题
通过Lock
