Java におけるマルチスレッド スタベーション現象の問題と解決策

package readerWriter; public class File { private String name; public File(String name) { this.name=name; } }

package readerWriter; public class Pool { private int readerNumber=0; private int writerNumber=0; private boolean waittingWriten; public boolean isWaittingWriten() { return waittingWriten; } public void setWaittingWriten(boolean waittingWriten) { this.waittingWriten = waittingWriten; } public File getFile() { return file; } public void setFile(File file) { this.file = file; } File file; public Pool(File file) { this.file=file; } public int getReaderNumber() { return readerNumber; } public void setReaderNumber(int readerNumber) { this.readerNumber = readerNumber; } public int getWriterNumber() { return writerNumber; } public void setWriterNumber(int writerNumber) { this.writerNumber = writerNumber; } }

package readerWriter; public class Reader implements Runnable{ private String id; private Pool pool; public Reader(String id,Pool pool) { this.id=id; this.pool=pool; } @Override public void run() { // TODO Auto-generated method stub while(!Thread.currentThread().interrupted()){ synchronized(pool){ while(pool.getWriterNumber()>0 || pool.isWaittingWriten()==true)//当线程正在写或者 //有线程正在等待写，则禁止读线程继续读 { try { pool.wait(); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } } { pool.setReaderNumber(pool.getReaderNumber()+1); } } System.out.println(id+" "+"is reading...."); try { Thread.sleep(1000); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } synchronized(pool) { pool.setReaderNumber(pool.getReaderNumber()-1); System.out.println(id+" "+"is existing the reader...."); if(pool.getReaderNumber()==0) pool.notifyAll(); } try { Thread.sleep(1000); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } // pool.notifyAll(); } } }

package readerWriter; public class Writer implements Runnable{ private Pool pool; String id; public Writer(String id,Pool pool) { this.id=id; this.pool=pool; } @Override public void run() { // TODO Auto-generated method stub while(!Thread.currentThread().interrupted()){ synchronized(pool){ if(pool.getReaderNumber()>0) pool.setWaittingWriten(true); else pool.setWaittingWriten(false); //当线程正在被读或者被写或者有线程等待读 while(pool.getWriterNumber()>0 || pool.getReaderNumber()>0) { try { pool.wait(); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } } pool.setWaittingWriten(false); //这个策略还算公平 { pool.setWriterNumber(pool.getWriterNumber()+1); } } System.out.println(id+" "+"is writing...."); try { Thread.sleep(1000); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } // synchronized(pool) { pool.setWriterNumber(pool.getWriterNumber()-1); System.out.println(id+" "+"is existing the writer...."); pool.notifyAll(); } /* try { Thread.sleep(1000); //System.out.println("writer sleeping over"); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } */ } } }

package readerWriter; public class Main { public static void main(String[] args) { // TODO Auto-generated method stub Pool pool=new Pool(new File("dd file")); for(int i=0;i<2;i++) { Thread writer=new Thread(new Writer("writer "+i,pool)); writer.start(); } for(int i=0;i<5;i++) { Thread reader=new Thread(new Reader("reader "+i,pool)); reader.start(); } } }

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