根据b站UP主狂神说JUC课程所写的个人学习笔记 视频地址：https://www.bilibili.com/video/BV1B7411L7tE?from=search&seid=14761503393031794075
锁是什么？如何判断锁的是谁
4.生产者和消费者问题
synchronized版本 wait notify
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 num = 0;
//+1
public synchronized void increment() throws InterruptedException {
if (num !=0){
//等待
this.wait();
}
num ++;
System.out.println(Thread.currentThread().getName()+"=>"+num);
//通知其他线程我加完毕了
this.notifyAll();
}
//-1
public synchronized void decrement() throws InterruptedException {
if (num ==0){
//等待
this.wait();
}
num --;
System.out.println(Thread.currentThread().getName()+"=>"+num);
//通知其他线程我减完毕了
this.notifyAll();
}
}
问题存在A B C D 4个线程
防止虚假唤醒问题把if改为while
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();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.increment();
} 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 num = 0;
//+1
public synchronized void increment() throws InterruptedException {
while (num !=0){
//等待
this.wait();
}
num ++;
System.out.println(Thread.currentThread().getName()+"=>"+num);
//通知其他线程我加完毕了
this.notifyAll();
}
//-1
public synchronized void decrement() throws InterruptedException {
while (num ==0){
//等待
this.wait();
}
num --;
System.out.println(Thread.currentThread().getName()+"=>"+num);
//通知其他线程我减完毕了
this.notifyAll();
}
}
JUC版的生产者和消费者问题
通过lock可以找到condition
代码实现
public class B {
public static void main(String[] args) {
Data2 data = new Data2();
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();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
data.increment();
} 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 Data2{
private int num = 0;
Lock lock = new ReentrantLock();
Condition condition = lock.newCondition();
//+1
public void increment() throws InterruptedException {
try {
lock.lock();
//业务代码
while (num !=0){
//等待
condition.await(); //等待
}
num ++;
System.out.println(Thread.currentThread().getName()+"=>"+num);
//通知其他线程我加完毕了
condition.signalAll();//唤醒全部
} catch (Exception e) {
e.printStackTrace();
}finally {
lock.unlock();
}
}
//-1
public void decrement() throws InterruptedException {
try {
lock.lock();
while (num ==0){
//等待
condition.await();
}
num --;
System.out.println(Thread.currentThread().getName()+"=>"+num);
//通知其他线程我减完毕了
condition.signalAll();
} catch (Exception e) {
e.printStackTrace();
}finally {
lock.unlock();
}
}
}
Condition实现精准通知唤醒
public class C {
public static void main(String[] args) {
Data3 data = new Data3();
new Thread(()->{
for (int i = 0; i < 10; i++) {
data.printA();
}
},"A").start();
new Thread(()->{
for (int i = 0; i < 10; i++) {
data.printB();
}
},"B").start();
new Thread(()->{
for (int i = 0; i < 10; i++) {
data.printC();
}
},"C").start();
}
}
class Data3{
private Lock lock = new ReentrantLock();
private Condition condition1 = lock.newCondition();
private Condition condition2 = lock.newCondition();
private Condition condition3 = lock.newCondition();
private int num = 1;
public void printA(){
lock.lock();
try {
while (num!=1){
condition1.await();
}
System.out.println(Thread.currentThread().getName()+"AAA");
num = 2;
condition2.signal();
} catch (Exception e) {
e.printStackTrace();
}finally {
lock.unlock();
}
}
public void printB(){
lock.lock();
try {
while (num!=2){
condition2.await();
}
System.out.println(Thread.currentThread().getName()+"BBB");
num =3;
condition3.signal();
} catch (Exception e) {
e.printStackTrace();
}finally {
lock.unlock();
}
}
public void printC(){
lock.lock();
try {
while (num!=3){
condition3.await();
}
System.out.println(Thread.currentThread().getName()+"CCC");
num = 1;
condition1.signal();
} catch (Exception e) {
e.printStackTrace();
}finally {
lock.unlock();
}
}
}