并发阶段任务中的阶段切换
这个方法默认实现如下：如果注册的参与者数量为0就返回true,否则就返回false。但是我们可以通过继承Phaser类覆盖这个方法。
package com.packtpub.java7.concurrency.chapter3.recipe6.task;
import java.util.concurrent.Phaser;
/**
* Implements a subclass of the Phaser class. Overrides the onAdvance method to control
* the change of phase
*
*/
public class MyPhaser extends Phaser {
/**
* This method is called when the last register thread calls one of the advance methods
* in the actual phase
* @param phase Actual phase
* @param registeredParties Number of registered threads
* @return false to advance the phase, true to finish
*/
@Override
protected boolean onAdvance(int phase, int registeredParties) {
switch (phase) {
case 0:
return studentsArrived();
case 1:
return finishFirstExercise();
case 2:
return finishSecondExercise();
case 3:
return finishExam();
default:
return true;
}
}
/**
* This method is called in the change from phase 0 to phase 1
* @return false to continue with the execution
*/
private boolean studentsArrived() {
System.out.printf("Phaser: The exam are going to start. The students are ready.\n");
System.out.printf("Phaser: We have %d students.\n",getRegisteredParties());
return false;
}
/**
* This method is called in the change from phase 1 to phase 2
* @return false to continue with the execution
*/
private boolean finishFirstExercise() {
System.out.printf("Phaser: All the students has finished the first exercise.\n");
System.out.printf("Phaser: It's turn for the second one.\n");
return false;
}
/**
* This method is called in the change form phase 2 to phase 3
* @return false to continue with the execution
*/
private boolean finishSecondExercise() {
System.out.printf("Phaser: All the students has finished the second exercise.\n");
System.out.printf("Phaser: It's turn for the third one.\n");
return false;
}
/**
* This method is called in the change from phase 3 to phase 4
* @return true. There are no more phases
*/
private boolean finishExam() {
System.out.printf("Phaser: All the students has finished the exam.\n");
System.out.printf("Phaser: Thank you for your time.\n");
return true;
}
}
package com.packtpub.java7.concurrency.chapter3.recipe6.task;
import java.util.Date;
import java.util.concurrent.Phaser;
import java.util.concurrent.TimeUnit;
/**
* This class implements an student in the exam
*
*/
public class Student implements Runnable {
/**
* Phaser to control the execution
*/
private Phaser phaser;
/**
* Constructor of the class. Initialize its objects
* @param phaser Phaser to control the execution
*/
public Student(Phaser phaser) {
this.phaser=phaser;
}
/**
* Main method of the student. It arrives to the exam and does three exercises. After each
* exercise, it calls the phaser to wait that all the students finishes the same exercise
*/
public void run() {
System.out.printf("%s: Has arrived to do the exam. %s\n",Thread.currentThread().getName(),new Date());
phaser.arriveAndAwaitAdvance();
System.out.printf("%s: Is going to do the first exercise. %s\n",Thread.currentThread().getName(),new Date());
doExercise1();
System.out.printf("%s: Has done the first exercise. %s\n",Thread.currentThread().getName(),new Date());
phaser.arriveAndAwaitAdvance();
System.out.printf("%s: Is going to do the second exercise. %s\n",Thread.currentThread().getName(),new Date());
doExercise2();
System.out.printf("%s: Has done the second exercise. %s\n",Thread.currentThread().getName(),new Date());
phaser.arriveAndAwaitAdvance();
System.out.printf("%s: Is going to do the third exercise. %s\n",Thread.currentThread().getName(),new Date());
doExercise3();
System.out.printf("%s: Has finished the exam. %s\n",Thread.currentThread().getName(),new Date());
phaser.arriveAndAwaitAdvance();
}
/**
* Does an exercise is to wait a random time
*/
private void doExercise1() {
try {
Long duration=(long)(Math.random()*10);
TimeUnit.SECONDS.sleep(duration);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
/**
* Does an exercise is wait a random time
*/
private void doExercise2() {
try {
Long duration=(long)(Math.random()*10);
TimeUnit.SECONDS.sleep(duration);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
/**
* Does an exercise is wait a random time
*/
private void doExercise3() {
try {
Long duration=(long)(Math.random()*10);
TimeUnit.SECONDS.sleep(duration);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
package com.packtpub.java7.concurrency.chapter3.recipe6.core;
import com.packtpub.java7.concurrency.chapter3.recipe6.task.MyPhaser;
import com.packtpub.java7.concurrency.chapter3.recipe6.task.Student;
/**
* Main class of the example
*
*/
public class Main {
/**
* Main method of the example
* @param args
*/
public static void main(String[] args) {
// Creates the Phaser
MyPhaser phaser=new MyPhaser();
// Creates 5 students and register them in the phaser
Student students[]=new Student[5];
for (int i=0; i<students.length; i++){
students[i]=new Student(phaser);
phaser.register();
}
// Create 5 threads for the students and start them
Thread threads[]=new Thread[students.length];
for (int i=0; i<students.length; i++) {
threads[i]=new Thread(students[i],"Student "+i);
threads[i].start();
}
// Wait for the finalization of the threads
for (int i=0; i<threads.length; i++) {
try {
threads[i].join();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
// Check that the Phaser is in the Terminated state
System.out.printf("Main: The phaser has finished: %s.\n",phaser.isTerminated());
}
}
工作原理
这个范例模拟了有三道试题的考试过程。所有的学生必须昨晚第一道题才可以开始做第二题。为了实现同步，我们使用了Phaser类，并且通过继承Phaser类和覆盖onAdvance()方法，实现自己的Phaser。
控制台运行结果
Student 0: Has arrived to do the exam. Wed Apr 30 09:53:13 CST 2014
Student 1: Has arrived to do the exam. Wed Apr 30 09:53:13 CST 2014
Student 2: Has arrived to do the exam. Wed Apr 30 09:53:13 CST 2014
Student 4: Has arrived to do the exam. Wed Apr 30 09:53:13 CST 2014
Student 3: Has arrived to do the exam. Wed Apr 30 09:53:13 CST 2014
Phaser: The exam are going to start. The students are ready.
Phaser: We have 5 students.
Student 3: Is going to do the first exercise. Wed Apr 30 09:53:13 CST 2014
Student 4: Is going to do the first exercise. Wed Apr 30 09:53:13 CST 2014
Student 2: Is going to do the first exercise. Wed Apr 30 09:53:13 CST 2014
Student 1: Is going to do the first exercise. Wed Apr 30 09:53:13 CST 2014
Student 0: Is going to do the first exercise. Wed Apr 30 09:53:13 CST 2014
Student 3: Has done the first exercise. Wed Apr 30 09:53:16 CST 2014
Student 0: Has done the first exercise. Wed Apr 30 09:53:19 CST 2014
Student 2: Has done the first exercise. Wed Apr 30 09:53:20 CST 2014
Student 1: Has done the first exercise. Wed Apr 30 09:53:20 CST 2014
Student 4: Has done the first exercise. Wed Apr 30 09:53:21 CST 2014
Phaser: All the students has finished the first exercise.
Phaser: It's turn for the second one.
Student 4: Is going to do the second exercise. Wed Apr 30 09:53:21 CST 2014
Student 0: Is going to do the second exercise. Wed Apr 30 09:53:21 CST 2014
Student 3: Is going to do the second exercise. Wed Apr 30 09:53:21 CST 2014
Student 1: Is going to do the second exercise. Wed Apr 30 09:53:21 CST 2014
Student 2: Is going to do the second exercise. Wed Apr 30 09:53:21 CST 2014
Student 0: Has done the second exercise. Wed Apr 30 09:53:22 CST 2014
Student 4: Has done the second exercise. Wed Apr 30 09:53:22 CST 2014
Student 3: Has done the second exercise. Wed Apr 30 09:53:26 CST 2014
Student 2: Has done the second exercise. Wed Apr 30 09:53:26 CST 2014
Student 1: Has done the second exercise. Wed Apr 30 09:53:26 CST 2014
Phaser: All the students has finished the second exercise.
Phaser: It's turn for the third one.
Student 1: Is going to do the third exercise. Wed Apr 30 09:53:26 CST 2014
Student 0: Is going to do the third exercise. Wed Apr 30 09:53:26 CST 2014
Student 3: Is going to do the third exercise. Wed Apr 30 09:53:26 CST 2014
Student 2: Is going to do the third exercise. Wed Apr 30 09:53:26 CST 2014
Student 2: Has finished the exam. Wed Apr 30 09:53:26 CST 2014
Student 4: Is going to do the third exercise. Wed Apr 30 09:53:26 CST 2014
Student 4: Has finished the exam. Wed Apr 30 09:53:32 CST 2014
Student 1: Has finished the exam. Wed Apr 30 09:53:32 CST 2014
Student 0: Has finished the exam. Wed Apr 30 09:53:34 CST 2014
Student 3: Has finished the exam. Wed Apr 30 09:53:34 CST 2014
Phaser: All the students has finished the exam.
Phaser: Thank you for your time.
Main: The phaser has finished: true.