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多线程15-线程案例
1. 案例一
现有的程序代码模拟产生了16个日志对象,并且需要运行16秒才能打印完这些日志,请在程序中增加4个线程去调用parseLog()方法来分别打印这16个日志对象,
程序只需要运行4秒即可打印完这些日志对象,代码如下:
package read; public class Test { public static void main(String[] args){ System.out.println("begin:"+(System.currentTimeMillis()/1000)); for(int i=0;i<16;i++){ //这行代码不能改动 final String log = ""+(i+1);//这行代码不能改动 { Test.parseLog(log); } } } //parseLog方法内部的代码不能改动 public static void parseLog(String log){ System.out.println(log+":"+(System.currentTimeMillis()/1000)); try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } } }
解答:
package read;import java.util.concurrent.ArrayBlockingQueue;import java.util.concurrent.BlockingQueue;import java.util.concurrent.ExecutorService;import java.util.concurrent.Executors; public class Test { public static void main(String[] args) throws Exception{ ExecutorService threadPool = Executors.newFixedThreadPool(4) ; final BlockingQueue<String> queue = new ArrayBlockingQueue<String>(16) ; //队列长度为16 for(int i = 1 ;i<=4 ;i++){ Runnable runnable = new Runnable() { public void run() { try { for(int i = 0 ;i<4;i++) Test.parseLog(queue.take()) ; if(queue.size()==0){ System.out.println("end:"+(System.currentTimeMillis()/1000)); } } catch (InterruptedException e) { e.printStackTrace(); } } }; threadPool.execute(runnable) ; } System.out.println("begin:"+(System.currentTimeMillis()/1000)); for(int i=0;i<16;i++){ //这行代码不能改动 final String log = ""+(i+1);//这行代码不能改动 { // Test.parseLog(log); queue.put(log) ; } } } //parseLog方法内部的代码不能改动 public static void parseLog(String log){ System.out.println(log+":"+(System.currentTimeMillis()/1000)); try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } } }
2.案例二
现成程序中的Test类中的代码在不断地产生数据,然后交给TestDo.doSome()方法去处理,就好像生产者在不断地产生数据,消费者在不断消费数据。请将程序改造成有10个线程来消费生成者产生
数据,这些消费者都调用TestDo.doSome()方法去进行处理,故每个消费者都需要一秒才能处理完,程序应保证这些消费者线程依次有序地消费数据,只有上一个消费者消费完后,下一个消费者才能消
费数据,下一个消费者是谁都可以,但要保证这些消费者线程拿到的数据是有顺序的
package queue; public class Test { public static void main(String[] args) { System.out.println("begin:"+(System.currentTimeMillis()/1000)); for(int i=0;i<10;i++){ //这行不能改动 String input = i+""; //这行不能改动 String output = TestDo.doSome(input); System.out.println(Thread.currentThread().getName()+ ":" + output); } } } //不能改动此TestDo类 class TestDo { public static String doSome(String input){ try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } String output = input + ":"+ (System.currentTimeMillis() / 1000); return output; } }
解答:
package queue;import java.util.concurrent.Semaphore;import java.util.concurrent.SynchronousQueue;public class Test { public static void main(String[] args) { final Semaphore semaphore = new Semaphore(1); final SynchronousQueue<String> queue = new SynchronousQueue<String>(); for(int i=0;i<10;i++){ new Thread(new Runnable(){ @Override public void run() { try { semaphore.acquire(); String input = queue.take(); String output = TestDo.doSome(input); System.out.println(Thread.currentThread().getName()+ ":" + output); semaphore.release(); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } } }).start(); } System.out.println("begin:"+(System.currentTimeMillis()/1000)); for(int i=0;i<10;i++){ //这行不能改动 String input = i+""; //这行不能改动 try { queue.put(input); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } } }}//不能改动此TestDo类class TestDo { public static String doSome(String input){ try { Thread.sleep(1000); } catch (InterruptedException e) { e.printStackTrace(); } String output = input + ":"+ (System.currentTimeMillis() / 1000); return output; }}
3.案例三
现有程序同时启动了4个线程去调用TestDo.doSome(key, value)方法,由于TestDo.doSome(key, value)方法内的代码是先暂停1秒,然后再输出以秒为单位的当前时间值,所以,会打印出4个相同的时间值,如下所示:
4:4:1258199615
1:1:1258199615
3:3:1258199615
1:2:1258199615
请修改代码,如果有几个线程调用TestDo.doSome(key, value)方法时,传递进去的key相等(equals比较为true),则这几个线程应互斥排队输出结果,即当有两个线程的key都是"1"时,它们中的一个要比另外其他线程晚1秒输出结果,如下所示:
4:4:1258199615
1:1:1258199615
3:3:1258199615
1:2:1258199616
总之,当每个线程中指定的key相等时,这些相等key的线程应每隔一秒依次输出时间值(要用互斥),如果key不同,则并行执行(相互之间不互斥)。原始代码如下:
package syn; //不能改动此Test类 public class Test extends Thread{ private TestDo testDo; private String key; private String value; public Test(String key,String key2,String value){ this.testDo = TestDo.getInstance(); /*常量"1"和"1"是同一个对象,下面这行代码就是要用"1"+""的方式产生新的对象, 以实现内容没有改变,仍然相等(都还为"1"),但对象却不再是同一个的效果*/ this.key = key+key2; this.value =http://www.mamicode.com/ value; } public static void main(String[] args) throws InterruptedException{ Test a = new Test("1","","1"); Test b = new Test("1","","2"); Test c = new Test("3","","3"); Test d = new Test("4","","4"); System.out.println("begin:"+(System.currentTimeMillis()/1000)); a.start(); b.start(); c.start(); d.start(); } public void run(){ testDo.doSome(key, value); } } class TestDo { private TestDo() {} private static TestDo _instance = new TestDo(); public static TestDo getInstance() { return _instance; } public void doSome(Object key, String value) { // 以大括号内的是需要局部同步的代码,不能改动! { try { Thread.sleep(1000); System.out.println(key+":"+value + ":" + (System.currentTimeMillis() / 1000)); } catch (InterruptedException e) { e.printStackTrace(); } } } }
解答:
package syn;import java.util.ArrayList;import java.util.Iterator;import java.util.concurrent.CopyOnWriteArrayList;//不能改动此Test类 public class Test extends Thread{ private TestDo testDo; private String key; private String value; public Test(String key,String key2,String value){ this.testDo = TestDo.getInstance(); /*常量"1"和"1"是同一个对象,下面这行代码就是要用"1"+""的方式产生新的对象, 以实现内容没有改变,仍然相等(都还为"1"),但对象却不再是同一个的效果*/ this.key = key+key2; /* a = "1"+""; b = "1"+""*/ this.value =http://www.mamicode.com/ value; } public static void main(String[] args) throws InterruptedException{ Test a = new Test("1","","1"); Test b = new Test("1","","2"); Test c = new Test("3","","3"); Test d = new Test("4","","4"); System.out.println("begin:"+(System.currentTimeMillis()/1000)); a.start(); b.start(); c.start(); d.start(); } public void run(){ testDo.doSome(key, value); }}class TestDo { private TestDo() {} private static TestDo _instance = new TestDo(); public static TestDo getInstance() { return _instance; } //private ArrayList keys = new ArrayList(); private CopyOnWriteArrayList keys = new CopyOnWriteArrayList(); public void doSome(Object key, String value) { Object o = key; if(!keys.contains(o)){ keys.add(o); }else{ for(Iterator iter=keys.iterator();iter.hasNext();){ try { Thread.sleep(20); } catch (InterruptedException e) { // TODO Auto-generated catch block e.printStackTrace(); } Object oo = iter.next(); if(oo.equals(o)){ o = oo; break; } } } synchronized(o) // 以大括号内的是需要局部同步的代码,不能改动! { try { Thread.sleep(1000); System.out.println(key+":"+value + ":" + (System.currentTimeMillis() / 1000)); } catch (InterruptedException e) { e.printStackTrace(); } } }}