JAVA學習筆記-Semaphore和CountDownLatch實例

Semaphore和CountDownLatch實例

直接上代碼，記錄一下Java併發學習中的線程同步輔助類Semaphore和CountDownLatch使用

package com.petecc.platform.foodsafe.concurrent.semaphore;

import java.util.Random;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**   
 * @Description 信號量Semaphore測試
 * @author tanw   
 * @date 2015年11月15日 下午8:42:05
 */
public class Main {

    public static void main(String[] args) {
        int THREAD_SIZE = 10;

        //線程結束批示,CountDownLatch只准進入一次，一旦內部計數器到達0，只能重新new
        CountDownLatch endLatch = new CountDownLatch(THREAD_SIZE);

        Printer printer = new Printer();

        Thread[] threads = new Thread[10];

        for(int i=0; i<threads.length;i++){
            threads[i] = new Thread(new PrintJob(printer,endLatch),"PrintJob"+i);
        }

        for(int i=0; i<threads.length;i++){
            threads[i].start();
        }

        try {
            endLatch.await();//等待所有線程結束
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        System.out.println("It is end in MAIN thread!");
    }

}

class PrintJob implements Runnable{
    private Printer printer;
    private CountDownLatch endLatch;

    public PrintJob(Printer printer,CountDownLatch endLatch) {
        super();
        this.printer = printer;
        this.endLatch = endLatch;
    }

    @Override
    public void run() {
        String printObj = "doc"+new Random().nextInt(1000);
        printer.printJob(printObj);
        endLatch.countDown();//完成任務
        System.out.printf("%s end print job, endLatch getCount()=%d\n",Thread.currentThread().getName(),endLatch.getCount());
    }

}

class Printer{

    private Semaphore semaphore;    //信號量
    private boolean[] freePrinters; //所有可用的打印機
    private Lock printlock;

    public Printer(){
        semaphore = new Semaphore(3);
        freePrinters = new boolean[3];
        for(int i=0; i<freePrinters.length; i++){
            freePrinters[i] = true;
        }
        printlock = new ReentrantLock();
    }

    public void printJob(Object obj){
        try {
            semaphore.acquire();

            int printerIdx = getValidPrinter();
            System.out.printf("\t\t%s use PRINTER %d print %s\n",Thread.currentThread().getName(),
                    printerIdx,obj.toString());

            long duration = new Random().nextInt(5);
            TimeUnit.SECONDS.sleep(duration);

            System.out.printf("\t\t%s finish print job in duration %d second\n",Thread.currentThread().getName(),duration);

            freePrinters[printerIdx] = true;
        } catch (InterruptedException e) {
            e.printStackTrace();
        }finally{
            semaphore.release();
        }
    }

    public int getValidPrinter(){
        int ret = -1;
        try{
            printlock.lock();
            for(int i=0; i<freePrinters.length; i++){
                if(freePrinters[i]){
                    ret = i;
                    freePrinters[i] = false;

                    break;
                }
            }
        }catch(Exception e){
            e.printStackTrace();
        }finally{
            printlock.unlock();
        }
        return ret;
    }
}