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秒杀多线程第十一篇 读者写者问题（续）
java实现：
本问题的关键是读者写者之间的同步问题，尤其使用java来操作。
1.等待读者，使用CountDownLatch mReaderLatch， 但是CountDownLatch只能使用一次，所以需要每次都new 一个。
或者可以考虑使用semaphore代替，但是semaphore需要acquire（READ_THREAD_SIZE）才能等待所有读者线程结束。
2.等待写入操作。使用semaphore来控制， mWriteSema.release(READ_THREAD_SIZE);表示读者都可以同时操作。
关键代码如下：
public void waitReaderEnd() { //多个read End,using countdownlatch try { mReaderLatch.await(); mReaderLatch = new CountDownLatch(READ_THREAD_SIZE); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } } public void singalWriteEnd(){ mWriteSema.release(READ_THREAD_SIZE); } public void waitWriteEnd(){ try { mWriteSema.acquire(); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } } public void singalReadEnd(){ mReaderLatch.countDown(); } public void initReadNone(){ try { mWriteSema.acquire(READ_THREAD_SIZE); for(int i=0;i<READ_THREAD_SIZE;i++) { mReaderLatch.countDown(); } } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } }
详细代码如下：
package com.multithread.readwrite;import java.util.ArrayList;import java.util.LinkedList;import java.util.List;import java.util.Queue;import java.util.concurrent.BrokenBarrierException;import java.util.concurrent.CountDownLatch;import java.util.concurrent.CyclicBarrier;import java.util.concurrent.Executor;import java.util.concurrent.Executors;import java.util.concurrent.Semaphore;import com.multithread.main.ExampleInterface;import com.multithread.prosumer.ProducerThread;/** * 1.写者要等待所有读者读完才能继续写入。 * 2.所有读者要等待写者写完才能继续读取。 * 3.读者这件可以共享读取文件。 * * * * */public class ReaderWriterExample extends ExampleInterface { public static final int READ_THREAD_SIZE = 4; public static final int BUFFER_LENGTH = 100; public List<Integer> g_productor = new ArrayList<Integer>(); public CountDownLatch mReaderLatch = new CountDownLatch(READ_THREAD_SIZE); public Semaphore mWriteSema = new Semaphore(READ_THREAD_SIZE); public boolean bStopFlag = false; public CountDownLatch mLatchDown = new CountDownLatch(1+READ_THREAD_SIZE); public CountDownLatch mLatchStart = new CountDownLatch(1+READ_THREAD_SIZE); @Override public void startDemo() { // TODO Auto-generated method stub try { initReadNone(); bStopFlag = false; Executor mEcecutor = Executors.newFixedThreadPool(1+READ_THREAD_SIZE); mEcecutor.execute(new WriteThread(this,"Writer")); for(int i=1;i<=READ_THREAD_SIZE;i++) { mEcecutor.execute(new ReadThread(this,"Reader"+i)); } mLatchStart.await(); System.out.println("All Thread is runnning"); mLatchDown.await(); System.out.println("All Thread is Down"); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } } public void waitReaderEnd() { //多个read End,using countdownlatch try { mReaderLatch.await(); mReaderLatch = new CountDownLatch(READ_THREAD_SIZE); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } } public void singalWriteEnd(){ mWriteSema.release(READ_THREAD_SIZE); } public void waitWriteEnd(){ try { mWriteSema.acquire(); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } } public void singalReadEnd(){ mReaderLatch.countDown(); } public void initReadNone(){ try { mWriteSema.acquire(READ_THREAD_SIZE); for(int i=0;i<READ_THREAD_SIZE;i++) { mReaderLatch.countDown(); } } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } }}
package com.multithread.readwrite;public class ReadThread extends Thread { ReaderWriterExample mRwExample = null; String name = null; boolean flag = true; public ReadThread(ReaderWriterExample re,String name) { mRwExample = re; this.name = name; } @Override public void run() { mRwExample.mLatchStart.countDown(); while(flag) { //等待写入结束 mRwExample.waitWriteEnd(); //读取文件，直到本次末尾 //check 文件写入操作是否已经彻底结束，结束read线程。 int mReadLength = mRwExample.g_productor.size(); String mReadStr = ""; if(mReadLength>0) { for(Integer a:mRwExample.g_productor) { mReadStr+=String.format("%x", a); } System.out.println(name+"读取数据："+mReadStr); } if(mRwExample.bStopFlag) { flag = false; } //通知本次读者结束。 mRwExample.singalReadEnd(); } System.out.println(name+"读取数据结束"); mRwExample.mLatchDown.countDown(); } }
package com.multithread.readwrite;public class WriteThread extends Thread { ReaderWriterExample mRwExample = null; String name = null; int iFlag = 0; public WriteThread(ReaderWriterExample re,String name) { mRwExample = re; this.name = name; } @Override public void run() { mRwExample.mLatchStart.countDown(); int index = 0; while(index<ReaderWriterExample.BUFFER_LENGTH) { //等待所有读者结束读取操作。 mRwExample.waitReaderEnd(); int mWriteLength = (int) (Math.random()*9)+1;//1-10; if(mWriteLength >(ReaderWriterExample.BUFFER_LENGTH - index)) { mWriteLength = ReaderWriterExample.BUFFER_LENGTH - index; } //写入数据到文件最后 //check 写入数据到最后。 mRwExample.g_productor.clear(); int mParam = 0; String writeline = ""; for(int i=0;i<mWriteLength;i++) { mParam = (int) (Math.random()*14)+1;//0-E mRwExample.g_productor.add(mParam); writeline+= String.format("%1$x", mParam); } index = index +mWriteLength; System.out.println(name+"写入数据："+writeline+"\t 当前index："+index); if(index>=ReaderWriterExample.BUFFER_LENGTH) { mRwExample.bStopFlag = true; } //通知写入操作结束，可以读取。 mRwExample.singalWriteEnd(); iFlag++; } System.out.println(name+"线程操作结束"); mRwExample.mLatchDown.countDown(); } }
秒杀多线程第十一篇 读者写者问题（续）
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