生产者和消费者问题
生产者和消费者问题
面试：单例模式，排序算法，生产者和消费者，死锁
Synchronized版
Synchronized 加锁 ； wait 等待； notify 唤醒；
/**
* 线程之间的週信题：生产者和消赏者问题！等待唤，知唤
* 线程交替执行 A B操作问一个变量num=0
* A 生产num+1
* B 消费num-1
*/public class Test01 { 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();
}
}//等待，业务，通知class Data{ private int num = 0; //+1
public synchronized void increment() throws InterruptedException { if(num != 0){ //等待线程
this.wait();
}
num++; //通知其他线程，+1完毕
System.out.println(Thread.currentThread().getName() + "->" + num); this.notifyAll();
} //-1
public synchronized void decrement() throws InterruptedException { if(num == 0){ //等待线程
this.wait();
}
num--; //通知其他线程，-1完毕
System.out.println(Thread.currentThread().getName() + "->" + num); this.notifyAll();
}
}问题存在，现在是A，B线程，没有发现问题，如果有A,B,C,D四个线程，多一个加减线程，就会出现问题
问题原因：
线程会出现虚假唤醒的情况，线程等待应出现在while循环中，不是if判断中
public class Test01 { 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.decrement();
} 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();
}
}//等待，业务，通知class Data{ private int num = 0; //+1
public synchronized void increment() throws InterruptedException { while(num != 0){ //等待线程
this.wait();
}
num++; //通知其他线程，+1完毕
System.out.println(Thread.currentThread().getName() + "->" + num); this.notifyAll();
} //-1
public synchronized void decrement() throws InterruptedException { while(num == 0){ //等待线程
this.wait();
}
num--; //通知其他线程，-1完毕
System.out.println(Thread.currentThread().getName() + "->" + num); this.notifyAll();
}
}JUC版的生产者和消费者问题
通过Lock 找到 Condition
Lock lock = new ReentrantLock(); Condition condition = lock.newCondition();//加锁lock.lock();//释放锁lock.unlock();//等待线程condition.await();//通知其他线程condition.signalAll();
public class Test01 { /**
* 线程之间的週信题：生产者和消赏者问题！等待唤，知唤
* 线程交替执行 A B操作问一个变量num=0
* A num+1
* B num-1
*/
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.decrement();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, "C").start(); new Thread(() -> { for (int i = 0; i < 10; i++) { try {
data.increment();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, "D").start();
}
}//等待，业务，通知class Data { private int num = 0;
Lock lock = new ReentrantLock();
Condition condition = lock.newCondition(); //+1
public void increment() throws InterruptedException {
lock.lock(); try { while (num != 0) { //等待线程
condition.await();
}
num++; //通知其他线程，+1完毕
System.out.println(Thread.currentThread().getName() + "->" + num);
condition.signalAll();
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
} //-1
public void decrement() throws InterruptedException {
lock.lock(); try { while (num == 0) { //等待线程
condition.await();
}
num--; //通知其他线程，-1完毕
System.out.println(Thread.currentThread().getName() + "->" + num);
condition.signalAll();
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
}//随机分布A->1B->0A->1B->0A->1B->0A->1B->0A->1B->0A->1B->0A->1B->0A->1B->0A->1B->0A->1B->0D->1C->0D->1任何一个新的技术，绝对不是仅仅只是覆盖了原来的技术，优势和补充！
Condition 精准的通知和唤醒线程：可以有序执行线程
public class Test01 { /**
* Condition 精准的通知和唤醒线程A B C
*/
public static void main(String[] args) {
Data data = new Data(); new Thread(() -> { for (int i = 0; i < 10; i++) { try {
data.note1();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, "A").start(); new Thread(() -> { for (int i = 0; i < 10; i++) { try {
data.note2();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, "B").start(); new Thread(() -> { for (int i = 0; i < 10; i++) { try {
data.note3();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}, "C").start();
}
}//等待，业务，通知class Data { private int num = 1;
Lock lock = new ReentrantLock();
Condition condition1 = lock.newCondition();
Condition condition2 = lock.newCondition();
Condition condition3 = lock.newCondition(); public void note1() throws InterruptedException {
lock.lock(); try { while (num != 1) { //等待线程
condition1.await();
}
System.out.println(Thread.currentThread().getName() + "->" + num);
num = 2; //唤醒指定的人 B
condition2.signal();
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
} public void note2() throws InterruptedException {
lock.lock(); try { while (num != 2) { //等待线程
condition2.await();
}
System.out.println(Thread.currentThread().getName() + "->" + num); //唤醒指定的人 C
num = 3;
condition3.signal();
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
} public void note3() throws InterruptedException {
lock.lock(); try { while (num != 3) { //等待线程
condition3.await();
}
System.out.println(Thread.currentThread().getName() + "->" + num); //唤醒指定的人 A
num = 1;
condition1.signal();
} catch (Exception e) {
e.printStackTrace();
} finally {
lock.unlock();
}
}
}//线程顺序执行，比如生产线 ： 下单 -》 支付 -》交易 -》物流A->1B->2C->3A->1B->2C->3A->1B->2C->3A->1B->2C->3来源
生产者和消费者问题 - saxon宋 - 博客园
来源https://www.cnblogs.com/saxonsong/p/14727157.html