3 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，以下方式都是基于这两种模型来实现的。我们来基于一道常见的面试题目来分析
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
3.1 synchronized方案
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| public class TestVolatile {
public static void main(String[] args) {
DemoClass demoClass = new DemoClass();
new Thread(()->{
for (int i=0;i<5;i++){
demoClass.increment();
}
}).start();
new Thread(()->{
for (int i = 0; i < 5; i++) {
demoClass.decrement();
}
}).start();
}
}
class DemoClass{
private int number = 0;
public synchronized void increment(){
try {
while (number !=0 ){
this.wait();
}
number ++;
System.out.println("---"+Thread.currentThread().getName()+"加1的结果为："+number+"---");
notifyAll();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
public synchronized void decrement(){
try {
while (number ==0 ){
this.wait();
}
number --;
System.out.println("---"+Thread.currentThread().getName()+"减1的结果为："+number+"---");
notifyAll();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
|
3.2 Lock方案
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| class DemoClass{
private int number = 0;
private Lock lock = new ReentrantLock();
private Condition condition = lock.newCondition();
public void increment(){
try {
lock.lock();
while (number !=0){
condition.await();
}
number ++;
System.out.println("---"+Thread.currentThread().getName()+"加1的结果为："+number+"---");
condition.signalAll();
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void decrement(){
try {
lock.lock();
while (number ==0){
condition.await();
}
number --;
System.out.println("---"+Thread.currentThread().getName()+"减1的结果为："+number+"---");
condition.signalAll();
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
}
|
3.4 线程间定制化通信
3.4.1 案例介绍
==问题：A线程打印五次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
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| class DemoClass{
private String CODE = "A";
private Lock lock = new ReentrantLock();
private Condition conditionA = lock.newCondition();
private Condition conditionB = lock.newCondition();
private Condition conditionC = lock.newCondition();
public void printA(){
try {
lock.lock();
if (!CODE.equals("A")){
conditionA.await();
}
for (int i = 0; i < 5; i++) {
System.out.println("A");
}
CODE = "B";
conditionB.signalAll();
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void printB(){
try {
lock.lock();
if (!CODE.equals("B")){
conditionB.await();
}
for (int i = 0; i < 10; i++) {
System.out.println("B");
}
CODE = "C";
conditionC.signalAll();
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
public void printC(){
try {
lock.lock();
if (!CODE.equals("C")){
conditionC.await();
}
for (int i = 0; i < 15; i++) {
System.out.println("C");
}
CODE = "A";
conditionA.signalAll();
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
}
|
sychronized实现同步的基础：Java中的每一个对象都可以作为锁，具体表现为以下三种方式。
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