Java并发编程-10-在锁中使用多条件-生产者消费者问题

一、在锁中使用条件

一个锁可能关联一个或多个条件，这些条件通过Condition接口声明

目的是允许线程获取锁并且查看等待的某一个条件是否满足，如果不满足就挂起直到某个线程唤醒它们

二、模拟实现

fileMock是一个文件模拟类

Buffer是一个数据缓冲区

一个或者多个生产者读取fileMock的所有数据行，并且使用insert()方法将读取的数据行插入到缓冲区

三、注意

1、与锁绑定的所有条件对象都是通过Lock接口的newCondiction()方法创建的。

2、在使用条件的时候，必须获取这个条件绑定的锁，所以带条件的代码必须在调用Lock对象的Lock()方法和unlock()方法之间

3、当线程调用条件await()方法时，它将自动释放这个条件绑定的锁，其它线程才可以获取这个锁并且执行相同的操作，或者执行这个锁保护的另一个临界区代码

4、当一个线程调用了对象的signal()或者signallAll()方法后，一个或多个在该条件上挂起的线程将被唤醒

四、condition接口

测试代码：

package com.concurrent.threadSynchronize;import java.util.LinkedList;import java.util.concurrent.locks.Condition;import java.util.concurrent.locks.ReentrantLock;/** * 数据缓冲区类 *  * @author Nicholas *  * 被生产者和消费者共享 */public class Buffer {private LinkedList<String> buffer; // 存放共享数据private int maxSize; // buffer的长度private ReentrantLock reentrantLock; // 对修改buffer的代码块进行控制private Condition lines; // 两个condition属性private Condition space;private boolean pendingLines; // 判断缓冲区是否还有数据public Buffer(int maxSize) {this.maxSize = maxSize;buffer = new LinkedList<>();reentrantLock = new ReentrantLock();lines = reentrantLock.newCondition();space = reentrantLock.newCondition();pendingLines = true;}/** * 参数是传入的字符串，将字符串写入到缓冲区 * @param line */public void insert(String line) {//首先要获取锁reentrantLock.lock();//然后判断缓冲区是否还有空位try {//缓冲区已满，调用条件space的await()方法等待，知道出现空位while (buffer.size() == maxSize) {space.await();}//将line插入offer的末尾buffer.offer(line);System.out.println(Thread.currentThread().getName()+ "Inserted line " + buffer.size());//调用条件lines的signalAll()方法唤醒所有的线程lines.signalAll();} catch (InterruptedException e) {e.printStackTrace();} finally {reentrantLock.unlock();}}/** * 获取缓冲区的第一个字符串 * @return */public String get() {String line = null;//首先要获取锁reentrantLock.lock();//缓冲区是空的，那么调用条件lines的await()方法等待try {while ((buffer.size() == 0) && (hasPendingLines())) {lines.await();}//缓冲区有数据，那么取出buffer的第一个字符串if (hasPendingLines()) {line = buffer.poll();System.out.println(Thread.currentThread().getName()+ "line read " + buffer.size());//调用条件space的signalAll()方法唤醒所有等待的线程space.signalAll();}} catch (InterruptedException e) {e.printStackTrace();} finally {reentrantLock.unlock();}//将拿到的字符串返回return line;}public boolean hasPendingLines() {return pendingLines || buffer.size() > 0;}public void setPendingLines(boolean pendingLines) {this.pendingLines = pendingLines;}}

package com.concurrent.threadSynchronize;public class FileMock {private String[] context;// 存储文件内容private int index;// 行号//使用随机的字符串初始化public FileMock(int size, int length) {context = new String[size];for (int i = 0; i < size; i++) {StringBuilder stringBuilder = new StringBuilder(length);for (int j = 0; j < length; j++) {int indice = (int) (Math.random() * 255);stringBuilder.append((char) indice);}context[i] = stringBuilder.toString();}index = 0;}/** * 如果文件有可以处理的数据行，则返回true * 负责，返回false * @return */public boolean hasMoreLines() {return index < context.length;}/** * 返回属性index指定的行内容，并将index自动增加1 * @return */public String getLine() {if (this.hasMoreLines()) {System.out.println("Mock : " + (context.length - index));return context[index++];}return null;}}

package com.concurrent.threadSynchronize;import java.util.Random;public class Consumer implements Runnable {private Buffer buffer;public Consumer(Buffer buffer) {this.buffer = buffer;}@Overridepublic void run() {while (buffer.hasPendingLines()) {String line = buffer.get();processLine(line);}}public void processLine(String line) {try {Random random = new Random();Thread.sleep(random.nextInt(100));} catch (InterruptedException e) {e.printStackTrace();}}}

package com.concurrent.threadSynchronize;public class Producer implements Runnable {private FileMock fileMock;private Buffer buffer;public Producer(FileMock fileMock, Buffer buffer) {this.fileMock = fileMock;this.buffer = buffer;}@Overridepublic void run() {buffer.setPendingLines(true);while (fileMock.hasMoreLines()) {String line = fileMock.getLine();buffer.insert(line);}buffer.setPendingLines(false);}}

package com.concurrent.threadSynchronize;public class Main {public static void main(String[] args) {FileMock fileMock = new FileMock(100, 10);Buffer buffer = new Buffer(20);Producer producer = new Producer(fileMock, buffer);Thread threadProducer = new Thread(producer, "Producer");Consumer[] consumer = new Consumer[3];Thread[] threadConsumer = new Thread[3];for (int i = 0; i < 3; i++) {consumer[i] = new Consumer(buffer);threadConsumer[i] = new Thread(consumer[i], "Consumer " + i);}threadProducer.start();for (int i = 0; i < 3; i++) {threadConsumer[i].start();}}}