生產者-消費者(producer-consumer)問題,也稱作有界緩衝區(bounded-buffer)問題,兩個進程共享一個公共的固定大小的緩衝區。其中一個是生產者,用於將消息放入緩衝區;另外一個是消費者,用於從緩衝區中取出消息。問題出現在當緩衝區已經滿了,而此時生產者還想向其中放入一個新的數據項的情形,其解決方法是讓生產者此時進行休眠,等待消費者從緩衝區中取走了一個或者多個數據後再去喚醒它。同樣地,當緩衝區已經空了,而消費者還想去取消息,此時也可以讓消費者進行休眠,等待生產者放入一個或者多個數據時再喚醒它。
一,首先定義公共資源類,其中的變量number是保存的公共數據。並且定義兩個方法,增加number的值和減少number的值。由於多線程的原因,必須加上synchronized關鍵字,注意while判斷的條件。
- /**
- * 公共資源類
- */
- public class PublicResource {
- private int number = 0;
- /**
- * 增加公共資源
- */
- public synchronized void increace() {
- while (number != 0) {
- try {
- wait();
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- }
- number++;
- System.out.println(number);
- notify();
- }
- /**
- * 減少公共資源
- */
- public synchronized void decreace() {
- while (number == 0) {
- try {
- wait();
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- }
- number--;
- System.out.println(number);
- notify();
- }
- }
二,分別定義生產者線程和消費者線程,並模擬多次生產和消費,即增加和減少公共資源的number值
- /**
- * 生產者線程,負責生產公共資源
- */
- public class ProducerThread implements Runnable {
- private PublicResource resource;
- public ProducerThread(PublicResource resource) {
- this.resource = resource;
- }
- @Override
- public void run() {
- for (int i = 0; i < 10; i++) {
- try {
- Thread.sleep((long) (Math.random() * 1000));
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- resource.increace();
- }
- }
- }
- /**
- * 消費者線程,負責消費公共資源
- */
- public class ConsumerThread implements Runnable {
- private PublicResource resource;
- public ConsumerThread(PublicResource resource) {
- this.resource = resource;
- }
- @Override
- public void run() {
- for (int i = 0; i < 10; i++) {
- try {
- Thread.sleep((long) (Math.random() * 1000));
- } catch (InterruptedException e) {
- e.printStackTrace();
- }
- resource.decreace();
- }
- }
- }
三,模擬多個生產者和消費者操作公共資源的情形,結果須保證是在允許的範圍內。
- public class ProducerConsumerTest {
- public static void main(String[] args) {
- PublicResource resource = new PublicResource();
- new Thread(new ProducerThread(resource)).start();
- new Thread(new ConsumerThread(resource)).start();
- new Thread(new ProducerThread(resource)).start();
- new Thread(new ConsumerThread(resource)).start();
- new Thread(new ProducerThread(resource)).start();
- new Thread(new ConsumerThread(resource)).start();
- }
- }