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。
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
3.1 synchronized方案
使用 wait(); notify();
java
public class TestMain {
/**
● 交替加减
*/
public static void main(String[] args){
DemoClass demoClass = new DemoClass();
new Thread(() ->{
for (int i = 0; i < 5; i++) {
demoClass.increment();
}
}, "线程 A").start();
new Thread(() ->{
for (int i = 0; i < 5; i++) {
demoClass.decrement();
}
}, "线程 B").start();
}
}
java
class DemoClass{
//加减对象
private int number = 0;
/**
* 加 1
*/
public synchronized void increment() {
try {
while (number != 0){
this.wait();
}
number++;
System.out.println(currentThread().getName() + "加一成功,值为:" + number);
//唤醒其他的线程
notifyAll();
}catch (Exception e){
e.printStackTrace();
}
}
/**
* 减一
*/
public synchronized void decrement(){
try {
while (number != 1){
this.wait();
}
number--;
System.out.println(currentThread().getName() + "减一成功,值为:" + number);
notifyAll();
}catch (Exception e){
e.printStackTrace();
}
}
} 3.2 Lock 方案
使用 Condition condition.await(); condition.signal();
java
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
class DemoClass{
// 加减对象
private int number = 0;
// 声明锁
private Lock lock = new ReentrantLock();
// 声明钥匙
private Condition condition = lock.newCondition();
/**
* 加 1
*/
public void increment() {
try {
lock.lock(); // 加锁
while (number != 0){
condition.await(); //等待
}
number++;
System.out.println(currentThread().getName() + "加一成功,值为:" + number);
// 通知其他等待的线程
condition.signalAll();
}catch (Exception e){
e.printStackTrace();
}finally {
lock.unlock(); //释放锁
}
}
/**
* 减一
*/
public void decrement(){
try {
lock.lock();
while (number != 1){
condition.await();
}
number--;
System.out.println(currentThread().getName() + "减一成功,值为:" + number);
condition.signalAll();
}catch (Exception e){
e.printStackTrace();
}finally {
lock.unlock();
}
}
}
java
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
class DemoClass{
//通信对象:0--打印 A 1---打印 B 2----打印 C
private int number = 0;
//声明锁
private Lock lock = new ReentrantLock();
//声明钥匙 A
private Condition conditionA = lock.newCondition();
//声明钥匙 B
private Condition conditionB = lock.newCondition();
//声明钥匙 C
private Condition conditionC = lock.newCondition();
}3.4 线程间定制化通信
3.4.1 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
3.4.2 实现流程
代码如下：
java
// 标志位 AA 1 BB 2 CC 3
private int number = 1;
Lock lock = new ReentrantLock();
private Condition conditionA = lock.newCondition();
private Condition conditionB = lock.newCondition();
private Condition conditionC = lock.newCondition();
// 5 次
public void printA(int j){
try {
lock.lock();
while (number != 1){
conditionA.await();
}
System.out.println(currentThread().getName() + "输出 A,第" + j + " 轮开始");
// 输出 5 次 A
for (int i = 0; i < 5; i++) {
System.out.println("A");
}
// 修改标志位
number = 2;
//唤醒 B
conditionB.signal();
} catch (Exception e){
e.printStackTrace();
} finally {
lock.unlock();
}
}
// 10 次
public void printB(int j){
try {
lock.lock();
while (number != 2){
conditionB.await();
}
System.out.println(currentThread().getName() + "输出 B,第" + j + " 轮开始");
//输出 10 次 B
for (int i = 0; i < 10; i++) {
System.out.println("B");
}
// 修改标志位
number = 3;
//唤醒 C
conditionC.signal();
} catch (Exception e){
e.printStackTrace();
}finally {
lock.unlock();
}
}
// 15 次
public void printC(int j){
try {
lock.lock();
while (number != 3){
conditionC.await();
}
System.out.println(currentThread().getName() + "输出 C,第" + j + " 轮开始");
//输出 15 次 C
for (int i = 0; i < 15; i++) {
System.out.println("C");
}
System.out.println("-----------------------------------------");
// 修改标志位
number = 1;
//唤醒 A
conditionA.signal();
} catch (Exception e){
e.printStackTrace();
} finally {
lock.unlock();
}
} 测试类
java
/**
● 关键字实现线程交替加减
*/
public class TestVolatile {
/**
● 交替加减
● @param args
*/
public static void main(String[] args){
DemoClass demoClass = new DemoClass();
new Thread(() ->{
for (int i = 1; i <= 10; i++) {
demoClass.printA(i);
}
}, "A 线程").start();
new Thread(() ->{
for (int i = 1; i <= 10; i++) {
demoClass.printB(i);
}
}, "B 线程").start();
new Thread(() ->{
for (int i = 1; i <= 10; i++) {
demoClass.printC(i);
}
}, "C 线程").start();
}
}