java - 我如何检查动态线程是否结束

Question

我有 imageurl 数组，通过 DownloadFromUrl 函数下载，从我的函数调用，我使用线程，我不知道有多少图像 url，对于创建的每个图像下载单独的线程，毕竟我想开始一个 Activity 这些线程结束。

我怎么能得到所有这些线程，线程 sleep 时间越长就不能工作，这不是一个好的程序。我也不能通过静态变量计数计算到线程结束，因为有时图像无法下载或 url 损坏，或者连接未超时，

我现在有点迷茫了，弄清楚这些所有线程都结束的程序是什么？

public void DownloadFromUrl(String DownloadUrl, String fileName) {

               try {
                       File root = android.os.Environment.getExternalStorageDirectory();               

                       File dir = new File (root.getAbsolutePath() + "/"+Imageurl.facebookpage);
                   if(dir.exists()==false) {
                        dir.mkdirs();
                   }

                   URL url = new URL(DownloadUrl); //you can write here any link
                   File file = new File(dir, fileName);



                   /* Open a connection to that URL. */
                   URLConnection ucon = url.openConnection();

                   /*
                    * Define InputStreams to read from the URLConnection.
                    */
                   InputStream is = ucon.getInputStream();
                   BufferedInputStream bis = new BufferedInputStream(is);

                   /*
                    * Read bytes to the Buffer until there is nothing more to read(-1).
                    */
                   ByteArrayBuffer baf = new ByteArrayBuffer(5000);
                   int current = 0;
                   while ((current = bis.read()) != -1) {
                      baf.append((byte) current);
                   }


                   /* Convert the Bytes read to a String. */
                   FileOutputStream fos = new FileOutputStream(file);
                   fos.write(baf.toByteArray());
                   fos.flush();
                   fos.close();
                   LoginActivity.statsofdownload++;

                   Log.d("DownloadManager","file://"+file.getAbsolutePath());

           } catch (IOException e) {
               Imageurl.pagestat="space";
               Log.d("DownloadManager", "Error: " + e);
           }

        }




myfunction()
{
 for(String string : Imageurl.output) {
                            imagea++;
                        final   int ind =imagea;
                        final String ss=string;
                        new Thread(new Runnable() {
                                public void run() {
                                      DownloadFromUrl(ss,"IMAGE"+ind+".jpeg");
                                      File root = android.os.Environment.getExternalStorageDirectory();         




                                   Imageurl.newyearsvalues.add("file://"+root.getAbsolutePath() + "/"+Imageurl.facebookpage+ "/"+"IMAGE"+ind+".jpeg");

                              }
                                }).start();


                    }

//// now need to call an activity but how I will know that these thread all end
}

Answer 1

备选方案 1:将 ExecutorService 与 shutdown() 和 awaitTermination() 一起使用:

ExecutorService taskExecutor = Executors.newFixedThreadPool(noOfParallelThreads);
while(...) {
  taskExecutor.execute(new downloadImage());
}
taskExecutor.shutdown();
try {
  taskExecutor.awaitTermination(Long.MAX_VALUE, TimeUnit.NANOSECONDS);
} catch (InterruptedException e) {
  ...
}

基本上，shutdown() 所做的是阻止 ExecutorService 接受任何更多的线程请求。 awaitTermination() 等待直到 ExecutorService 完成所有线程的执行。

备选方案 2:使用 CountDownLatch:

CountDownLatch latch = new CountDownLatch(totalNumberOfImageDownloadTasks);
ExecutorService taskExecutor = Executors.newFixedThreadPool(noOfParallelThreads);
while(...) {
  taskExecutor.execute(new downloadImage());
}

try {
  latch.await();
} catch (InterruptedException E) {
   // handle
}

并在您的 imageDowloader() 函数中添加一行:

latch.countDown();

这将在每次执行时将 latch 的值递增 1。