多線程和信號量Semaphore

    信號量Semaphore是一個併發工具類，用來控制可同時併發的線程數，其內部維護了一組虛擬許可，通過構造器指定許可的數量，每次線程執行操作時先通過acquire方法獲得許可，執行完畢再通過release方法釋放許可。如果無可用許可，那麼acquire方法將一直阻塞，直到其它線程釋放許可。

 

比如說我們現在要處理一批訂單，（如下單，取消，或者對賬），訂單量比較多，才用多線程處理

先創建一個簡單訂單model示例

package test;

import java.io.Serializable;

/**
 * @Description
 * @Author penn
 * @Date 2019-08-28
 */
public class Order implements Serializable {
    private static final long serialVersionUID = 7592930394427200495L;

    private String orderId;

    private String orderName;

    public String getOrderId() {
        return orderId;
    }

    public void setOrderId(String orderId) {
        this.orderId = orderId;
    }

    public String getOrderName() {
        return orderName;
    }

    public void setOrderName(String orderName) {
        this.orderName = orderName;
    }
}

然後我們通過線程池去處理，最多10個線程，意思是同一時刻，最多10個線程在處理訂單業務

package test;

import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Semaphore;
import java.util.concurrent.TimeUnit;

/**
 * @Description
 * @Author penn
 * @Date 2019-08-28
 */
public class Gtest {
    private static SimpleDateFormat sf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS");

    public static void main(String args[]){

        try{

            ExecutorService executorService = Executors.newFixedThreadPool(10);
            final Semaphore semaphore       = new Semaphore(10);
            List<Order> persons = initData();
            for(Order p : persons){
                executorService.execute(() -> {
                    try {
                        semaphore.acquire();
                        System.out.println(p.getOrderId() + "," + p.getOrderName() + getFormatTimeStr());
                        //業務代碼開始
                        //業務代碼
                        //業務代碼結束
                        semaphore.release();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                });
            }
            executorService.shutdown();
            executorService.awaitTermination(1, TimeUnit.MINUTES);
        }catch (Exception e){
            System.out.println(e.getMessage());
        }
    }

    private static List<Order> initData(){
        List<Order> persons = new ArrayList<>();
        for(int i =0;i<100;i++){
            Order person = new Order();
            person.setOrderId("ID_" + (1000+i));
            person.setOrderName("NAME" + (1000+i));
            persons.add(person);
        }
        return persons;
    }

    public static String getFormatTimeStr() {
        return sf.format(new Date());
    }
}

處理完成後，記得關閉線程池！