Question

我有一个命令行应用程序。它运行循环说100次，并在循环中使用线程调度任务。我正在使用ExecutorService，因此任何时候都有4个线程在运行。

循环结束后，我想打印摘要消息。例如。完成所有100项任务所需的时间。当我逐步完成代码时，调试器直接进入摘要部分，但其他任务仍在运行。我理解这是因为每个线程都是自己运行的。那么如何在所有线程完成后才打印消息？

ExecutorService exec = Executors.newFixedThreadPool(4);

long startTime = System.currentTimeMillis();

for (int i = 0; i < 100; i++) {

    Runnable requestHandler = new Runnable() {
        @Override
        public void run() {
            try {
                // call task function in here
            } catch (Exception ex) {
            }
        }
    };
    exec.execute(requestHandler);
}

exec.shutdown();

long endTime = System.currentTimeMillis();

LOGGER.info("******************SUMMARY******************");
LOGGER.info("Time taken : " + ((endTime - startTime)/1000) + " seconds, " 
                            + ((endTime - startTime)/1000/60) + " minutes");

Answer 1

从主线程中，您可以创建另一个线程来执行从声明exec到exec.shutdown();的所有操作。创建此线程后，将主线程放到wait。在新主题的操作结束时（在exec.shutdown();之后），您应该notify它。

Answer 2

请参阅为简洁而复制的http://download.oracle.com/javase/6/docs/api/java/util/concurrent/ExecutorService.html示例

 void shutdownAndAwaitTermination(ExecutorService pool) {
   pool.shutdown(); // Disable new tasks from being submitted
   try {
     // Wait a while for existing tasks to terminate
     if (!pool.awaitTermination(60, TimeUnit.SECONDS)) {
       pool.shutdownNow(); // Cancel currently executing tasks
       // Wait a while for tasks to respond to being cancelled
       if (!pool.awaitTermination(60, TimeUnit.SECONDS))
           System.err.println("Pool did not terminate");
     }
   } catch (InterruptedException ie) {
     // (Re-)Cancel if current thread also interrupted
     pool.shutdownNow();
     // Preserve interrupt status
     Thread.currentThread().interrupt();
   }
 }

Answer 3

基本上你需要等到ExecutorService isTerminated()方法返回true。您可以使用awaitTermination()作为目的。

Answer 4

The solution for you based on your code:

ExecutorService exec = Executors.newFixedThreadPool(4);
long start = System.currentTimeMillis();
//Your code
exec.shutdown();
while(true) {
  if(exec.isTerminated()) {
    long end = System.currentTimeMillis();
    System.out.println("Time : " + (end - start));  
    break;
  }

Check this out! It works!

完成所有线程（池中）后如何打印摘要消息？

4 个答案: