JUC学习笔记(三)_线程间通信线程间通信的模型有两种:共享内存和消息传递,以下方式都是基本这两种模型来实现的。我们来基本一道面试常见的题目来分析


1、线程间通信

线程间通信的模型有两种:共享内存和消息传递,以下方式都是基本这两种模型来实现的。我们来基本一道面试常见的题目来分析

场景---两个线程,一个线程对当前数值加 1,另一个线程对当前数值减 1,要求用线程间通信

1.1、synchronized 方案

public class ThreadDemo1 {

public static void main(String[] args) {
Share share = new Share();

new Thread(() -> {
for (int i = 0; i < 10; i++) {
try {
share.increment();
} catch (Exception e) {
e.printStackTrace();
}
}
}, "AA").start();

new Thread(() -> {
for (int i = 0; i < 10; i++) {
try {
share.decrement();
} catch (Exception e) {
e.printStackTrace();
}
}
}, "BB").start();
}

}

class Share {

private int num = 0;

public synchronized void increment() throws Exception {
while (num != 0) {
this.wait();
}
num++;
System.out.println(Thread.currentThread().getName() + "::" + num);
this.notifyAll();

}

public synchronized void decrement() throws Exception {
while (num != 1) {
this.wait();
}
num--;
System.out.println(Thread.currentThread().getName() + "::" + num);
this.notifyAll();
}
}

1.2、Lock方案

public class ThreadDemo2 {

public static void main(String[] args) {
Share2 share = new Share2();

new Thread(() -> {
for (int i = 0; i < 10; i++) {
try {
share.increment();
} catch (Exception e) {
e.printStackTrace();
}
}
}, "AA").start();

new Thread(() -> {
for (int i = 0; i < 10; i++) {
try {
share.decrement();
} catch (Exception e) {
e.printStackTrace();
}
}
}, "BB").start();
}

}

class Share2 {

private Lock lock = new ReentrantLock();
private Condition condition = lock.newCondition();

private int num = 0;

public void increment() throws Exception {
lock.lock();
try {
while (num != 0) {
condition.await();
}
num++;
System.out.println(Thread.currentThread().getName() + "::" + num);
condition.signalAll();
} finally {
lock.unlock();
}

}

public void decrement() throws Exception {
lock.lock();
try {
while (num != 1) {
condition.await();
}
num--;
System.out.println(Thread.currentThread().getName() + "::" + num);
condition.signalAll();
} finally {
lock.unlock();
}
}
}

1.3、线程间定制化通信

1.3.1、案例介绍

问题: A 线程打印 5 次 A,B 线程打印 10 次 B,C 线程打印 15 次 C,按照此顺序循环 10 轮

1.3.2、实现流程

public class ThreadDemo3 {

public static void main(String[] args) {
ShareResource shareResource = new ShareResource();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
shareResource.print5(i);
} catch (Exception e) {
}
}
},"AA").start();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
shareResource.print10(i);
} catch (Exception e) {
}
}
},"BB").start();
new Thread(()->{
for (int i = 0; i < 10; i++) {
try {
shareResource.print15(i);
} catch (Exception e) {
}
}
},"CC").start();
}
}

class ShareResource {
// 定义标志位
private int flag = 1;
// 创建Lock锁
private Lock lock = new ReentrantLock();
private Condition c1 = lock.newCondition();
private Condition c2 = lock.newCondition();
private Condition c3 = lock.newCondition();

public void print5(int loop) throws Exception {
lock.lock();
try {
// 判断。防止虚假唤醒
while (flag != 1) {
// 等待
c1.await();
}
for (int i = 0; i < 5; i++) {
System.out.println(Thread.currentThread().getName() + "::" + loop);
}
// 修改标志位
flag = 2;
// 通知
c2.signal();
} finally {
lock.unlock();
}
}

public void print10(int loop) throws Exception {
lock.lock();
try {
while (flag != 2) {
c2.await();
}
for (int i = 0; i < 10; i++) {
System.out.println(Thread.currentThread().getName() + "::" + loop);
}
flag = 3;
c3.signal();
} finally {
lock.unlock();
}
}

public void print15(int loop) throws Exception {
lock.lock();
try {
while (flag != 3) {
c3.await();
}
for (int i = 0; i < 15; i++) {
System.out.println(Thread.currentThread().getName() + "::" + loop);
}
flag = 1;
c1.signal();
} finally {
lock.unlock();
}
}
}

JUC学习笔记(三)_共享内存_02