JUC学习笔记（一）https://www.cnblogs.com/lm66/p/15118407.html
JUC学习笔记（二）https://www.cnblogs.com/lm66/p/15118813.html
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();
}
}
}
