【发布时间】：2014-05-03 19:37:48
【问题描述】：
我遇到了一个多线程程序的问题。
我需要模拟很多人试图在同一时间预订同一航班，不使用任何锁。
所以我创建了一个 ExecutorService 并用它来池线程，这样我就可以同时进行许多尝试。
但问题是，程序在打印出所有结果之前就到达了终点，它只是坐在那里并永远运行。我试图进入所有其他使用数据库连接的类，并简单地手动关闭它们。没有运气。
package dbassignment4;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Future;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.RejectedExecutionException;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;
/**
*
* @author Vipar
*/
public class Master{
private static final int POOL_SIZE = 50;
public static boolean planeIsBooked = false;
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
int success = 0;
int seatNotReserved = 0;
int seatNotReservedByCustomerID = 0;
int reservationTimeout = 0;
int seatIsOccupied = 0;
int misc = 0;
HelperClass.clearAllBookings("CR9");
Thread t = new Thread(new DBMonitor("CR9"));
long start = System.nanoTime();
//HelperClass.clearAllBookings("CR9");
ExecutorService pool = new ThreadPoolExecutor(
POOL_SIZE, POOL_SIZE,
0L,
TimeUnit.MILLISECONDS,
new LinkedBlockingQueue<Runnable>(POOL_SIZE));
int threadsStarted = 0;
List<Future<Integer>> results = new ArrayList<>();
long id = 1;
t.start();
while(planeIsBooked == false) {
try {
Future<Integer> submit = pool.submit(new UserThread(id));
results.add(submit);
} catch (RejectedExecutionException ex) {
misc++;
continue;
}
threadsStarted++;
id++;
}
pool.shutdownNow();
int count = 0;
for(Future<Integer> i : results) {
try {
switch(i.get()) {
case 0:
// Success
success++;
break;
case -1:
// Seat is not Reserved
seatNotReserved++;
break;
case -2:
// Seat is not Reserved by Customer ID
seatNotReservedByCustomerID++;
break;
case -3:
// Reservation Timeout
reservationTimeout++;
break;
case -4:
// Seat is occupied
seatIsOccupied++;
break;
default:
misc++;
// Everything else fails
break;
}
} catch (ExecutionException | InterruptedException ex) {
misc++;
}
count++;
System.out.println("Processed Future Objects: " + count);
// HERE IS WHERE IT LOOPS
}
下面是它不会立即执行的其余代码：
long end = System.nanoTime();
long time = end - start;
System.out.println("Threads Started: " + threadsStarted);
System.out.println("Successful Bookings: " + success);
System.out.println("Seat Not Reserved when trying to book: " + seatNotReserved);
System.out.println("Reservations that Timed out: " + reservationTimeout);
System.out.println("Reserved by another ID when trying to book: " + seatNotReservedByCustomerID);
System.out.println("Bookings that were occupied: " + seatIsOccupied);
System.out.println("Misc Errors: " + misc);
System.out.println("Execution Time (Seconds): " + (double) (time / 1000000000));
}
}
你能发现问题吗？我在代码停止运行的地方添加了注释。
【问题讨论】：
-
永远永远这样做：
planeIsBooked == false。planeIsBooked == (true == false)更具可读性。或planeIsBooked == (1 == 2 == true)。你明白了。 -
为什么要关闭池？
-
我没有看到你停止
Thread t。还要使用Executors中的工厂方法，而不是构造函数。 -
@salyh 你好，我是最初想提交问题的人，但是我今天问的太多了。基本上我们关闭了游泳池，因为我们现在实现了预订飞机上每个座位的目标。
-
Further
planeIsBooked不是volatile，因此如果您从其他线程更新它，此更改将不可见。基本上，这段代码都是错的……
标签： java multithreading ojdbc