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java生产者消费者问题代码分析

發布時間：2023/12/10 编程问答 22 豆豆

生活随笔收集整理的這篇文章主要介紹了 java生产者消费者问题代码分析小編覺得挺不錯的,現在分享給大家,幫大家做個參考.

作者要的是一個生產者生成，接著必須有一個消費者消費，那這不是需要單線程嗎？或者使用1個大小的阻塞隊列。所以只談論問題本身，不談論好不好。

具體代碼：

Java代碼 ?

import?java.util.concurrent.locks.Condition; ??

import?java.util.concurrent.locks.Lock; ??

import?java.util.concurrent.locks.ReentrantLock; ??

//生產/消費者模式 ??

public?class?Basket?{ ??

????Lock?lock?=?new?ReentrantLock(); ??

????//?產生Condition對象 ??

????Condition?produced?=?lock.newCondition(); ??

????Condition?consumed?=?lock.newCondition(); ??

????boolean?available?=?false; ??

????public?void?produce()?throws?InterruptedException?{ ??

????????lock.lock(); ??

????????try?{ ??

????????????if?(available)?{ ??

????????????????produced.await();?//?放棄lock進入睡眠 ??

????????????} ??

????????????System.out.println("Apple?produced."); ??

????????????available?=?true; ??

????????????consumed.signal();?//?發信號喚醒等待這個Condition的線程 ??

????????}?finally?{ ??

????????????lock.unlock(); ??

????????} ??

????} ??

????public?void?consume()?throws?InterruptedException?{ ??

????????lock.lock(); ??

????????try?{ ??

????????????if?(!available)?{ ??

????????????????consumed.await();?//?放棄lock進入睡眠 ??

????????????} ??

????????????/*?吃蘋果?*/??

????????????System.out.println("Apple?consumed."); ??

????????????available?=?false; ??

????????????produced.signal();?//?發信號喚醒等待這個Condition的線程 ??

????????}?finally?{ ??

????????????lock.unlock(); ??

????????} ??

????} ??

}??

import java.util.concurrent.locks.Condition;import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReentrantLock;//生產/消費者模式public class Basket {Lock lock = new ReentrantLock();// 產生Condition對象Condition produced = lock.newCondition();Condition consumed = lock.newCondition();boolean available = false;public void produce() throws InterruptedException {lock.lock();try {if (available) {produced.await(); // 放棄lock進入睡眠}System.out.println("Apple produced.");available = true;consumed.signal(); // 發信號喚醒等待這個Condition的線程} finally {lock.unlock();}}public void consume() throws InterruptedException {lock.lock();try {if (!available) {consumed.await(); // 放棄lock進入睡眠}/* 吃蘋果 */System.out.println("Apple consumed.");available = false;produced.signal(); // 發信號喚醒等待這個Condition的線程} finally {lock.unlock();}}}

Java代碼 ?

import?java.util.concurrent.ExecutorService; ??

import?java.util.concurrent.Executors; ??

//測試用類 ??

public?class?ConditionTester?{ ??

????public?static?void?main(String[]?args)?throws?InterruptedException?{ ??

????????final?Basket?basket?=?new?Basket(); ??

????????//?定義一個producer ??

????????Runnable?producer?=?new?Runnable()?{ ??

????????????public?void?run()?{ ??

????????????????try?{ ??

????????????????????basket.produce(); ??

????????????????}?catch?(InterruptedException?ex)?{ ??

????????????????????ex.printStackTrace(); ??

????????????????} ??

????????????} ??

????????}; ??

????????//?定義一個consumer ??

????????Runnable?consumer?=?new?Runnable()?{ ??

????????????public?void?run()?{ ??

????????????????try?{ ??

????????????????????basket.consume(); ??

????????????????}?catch?(InterruptedException?ex)?{ ??

????????????????????ex.printStackTrace(); ??

????????????????} ??

????????????} ??

????????}; ??

????????//?各產生10個consumer和producer ??

????????ExecutorService?service?=?Executors.newCachedThreadPool(); ??

????????for?(int?i?=?0;?i?<?4;?i++) ??

????????????service.submit(consumer); ??

????????Thread.sleep(2000?*?2); ??

????????for?(int?i?=?0;?i?<?4;?i++) ??

????????????service.submit(producer); ??

????????service.shutdown(); ??

????} ??

}??

import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors;//測試用類 public class ConditionTester {public static void main(String[] args) throws InterruptedException {final Basket basket = new Basket();// 定義一個producerRunnable producer = new Runnable() {public void run() {try {basket.produce();} catch (InterruptedException ex) {ex.printStackTrace();}}};// 定義一個consumerRunnable consumer = new Runnable() {public void run() {try {basket.consume();} catch (InterruptedException ex) {ex.printStackTrace();}}};// 各產生10個consumer和producerExecutorService service = Executors.newCachedThreadPool();for (int i = 0; i < 4; i++)service.submit(consumer);Thread.sleep(2000 * 2);for (int i = 0; i < 4; i++)service.submit(producer);service.shutdown();} }

原因分析：

1、假設前面有2個producer(此時available=true)

1.1、一個在等待lock

1.2、一個await

2、consumer生成內容后，available=false，produced.signal(); 最后lock.unlock();

3.1、因為lock.unlock所以會觸發一個lock獲取到鎖（雖然signal也會觸發等待這個條件的其他線程，但是多線程大家都知道什么時候觸發這是不確定的），如果此時正好是[1.1]那么因為available=false，執行完釋放鎖

3.2、produced.signal()所以會觸發一個await的producer；

解決方案：

只要保證[3.1]還是需要await即可解決問題

所以加一個 AtomicInteger producedAwaitCounter = new AtomicInteger(0); 統計當前等待的生產者，如果當前available=false，但已經有生產者生成了內容，那么先等待消費者消費了再說

? ? ? ? ? ? if (available || producedAwaitCounter.get() > 0) {

? ? ? ? ? ? ? ? producedAwaitCounter.incrementAndGet();

? ? ? ? ? ? ? ? produced.await(); // 放棄lock進入睡眠

? ? ? ? ? ? ? ? producedAwaitCounter.decrementAndGet();

? ? ? ? ? ? }

當然最簡單的是使用：自旋，原理可以自己分析下：

? ? ? ? ? ? while (available) {

? ? ? ? ? ? ? ? produced.await(); // 放棄lock進入睡眠

? ? ? ? ? ? }

Java代碼 ?

package?com.sishuok.es.test; ??

import?java.util.concurrent.atomic.AtomicInteger; ??

import?java.util.concurrent.locks.Condition; ??

import?java.util.concurrent.locks.Lock; ??

import?java.util.concurrent.locks.ReentrantLock; ??

//生產/消費者模式 ??

public?class?Basket?{ ??

????Lock?lock?=?new?ReentrantLock(true); ??

//?產生Condition對象 ??

????Condition?produced?=?lock.newCondition(); ??

????Condition?consumed?=?lock.newCondition(); ??

????boolean?available?=?false; ??

????AtomicInteger?producedAwaitCounter?=?new?AtomicInteger(0); ??

????public?void?produce()?throws?InterruptedException?{ ??

????????lock.lock(); ??

????????try?{ ??

????????????if?(available?||?producedAwaitCounter.get()?>?0)?{ ??

????????????????producedAwaitCounter.incrementAndGet(); ??

????????????????produced.await();?//?放棄lock進入睡眠 ??

????????????????producedAwaitCounter.decrementAndGet(); ??

????????????} ??

????????????System.out.println("Apple?produced."); ??

????????????available?=?true; ??

????????????consumed.signal();?//?發信號喚醒等待這個Condition的線程 ??

????????}?finally?{ ??

????????????lock.unlock(); ??

????????} ??

????} ??

????public?void?consume()?throws?InterruptedException?{ ??

????????lock.lock(); ??

????????try?{ ??

????????????if?(!available)?{ ??

????????????????consumed.await();?//?放棄lock進入睡眠 ??

????????????} ??

????????????/*?吃蘋果?*/??

????????????System.out.println("Apple?consumed."); ??

????????????available?=?false; ??

????????????produced.signal();?//?發信號喚醒等待這個Condition的線程 ??

????????}?finally?{ ??

????????????lock.unlock(); ??

????????} ??

????} ??

}??

package com.sishuok.es.test;import java.util.concurrent.atomic.AtomicInteger; import java.util.concurrent.locks.Condition;import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReentrantLock;//生產/消費者模式public class Basket {Lock lock = new ReentrantLock(true);// 產生Condition對象Condition produced = lock.newCondition();Condition consumed = lock.newCondition();boolean available = false;AtomicInteger producedAwaitCounter = new AtomicInteger(0);public void produce() throws InterruptedException {lock.lock();try {if (available || producedAwaitCounter.get() > 0) {producedAwaitCounter.incrementAndGet();produced.await(); // 放棄lock進入睡眠producedAwaitCounter.decrementAndGet();}System.out.println("Apple produced.");available = true;consumed.signal(); // 發信號喚醒等待這個Condition的線程} finally {lock.unlock();}}public void consume() throws InterruptedException {lock.lock();try {if (!available) {consumed.await(); // 放棄lock進入睡眠}/* 吃蘋果 */System.out.println("Apple consumed.");available = false;produced.signal(); // 發信號喚醒等待這個Condition的線程} finally {lock.unlock();}}}

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