当所有任务完成时，异步写入appengine blob并完成它

问题描述

我有一个难题。

我遍历一组按日期参数化的URL并获取它们。例如，以下是一个示例：

somewebservice.com?start=01-01-2012&end=01-10-2012

有时，从URL返回的内容会被截断（缺少随机附带的'截断错误'消息），因为我定义了太大的范围，所以我必须将查询分解为两个网址

somewebservice.com?start=01-01-2012&end=01-05-2012

somewebservice.com?start=01-06-2012&end=01-10-2012

我以递归方式执行此操作，直到结果不再被截断，然后我写入一个blob，允许并发写入。

这些URL读取调用/ blob写入中的每一个都在单独的任务队列任务中处理。

问题是，我不能为了我的生活而设计一个方案来知道所有任务何时完成。我尝试过使用分片计数器，但递归使它很难。有人建议我使用Pipeline API，所以我观看了3次Slatkin的演讲。它似乎不适用于递归（但我承认我还没有完全理解这个库）。

有没有办法知道何时完成一组任务队列任务（以及递归产生的子项），以便我可以完成我的blob并对其进行任何操作？ / p>

谢谢，
John

解决方案

这是我所做的。我不得不稍微修改米奇的解决方案，但他肯定会让我朝着正确的方向发展，而不是立即返回未来的价值。

我必须创建一个中间层DummyJob，它接受递归的输出

  public static class DummyJob extends Job1< Void，List< Void>> {
 @Override 
 public Value< Void>运行（List< Void>傻瓜）{
 return null; 
 
 
  

然后，我将DummyJob的输出提交给Blob Finalizer in a waitFor

  List< FutureValue< Void>> dummies = new ArrayList< FutureValue< Void>>（）; 
 for（Interval in：ins）{
 dummies.add（futureCall（new DataFetcher（），immediate（file），immediate（in.getStart（）），
 immediate（in.getEnd （））））; 
} 
 
 FutureValue< Void> fv = futureCall（new DummyJob（），futureList（dummies））; 
 
 return futureCall（new DataWriter（），immediate（file），waitFor（fv））; 
  

谢谢米奇和尼克!!

I have a difficult problem.

I am iterating through a set of URLs parameterized by date and fetching them. For example, here is an example of one:

somewebservice.com?start=01-01-2012&end=01-10-2012

Sometimes, the content returned from the URL gets truncated (missing random results with a 'truncated error' message attached) because I've defined too large a range, so I have to split the query into two URLs

somewebservice.com?start=01-01-2012&end=01-05-2012

somewebservice.com?start=01-06-2012&end=01-10-2012

I do this recursively until the results aren't truncated anymore, and then I write to a blob, which allows concurrent writes.

Each of these URL fetch calls/blob writes is handled in a separate task queue task.

The problem is, I can't for the life of me devise a scheme to know when all the tasks have completed. I've tried using sharded counters, but the recursion makes it difficult. Someone suggested I use the Pipeline API, so I watched the Slatkin talk 3 times. It doesn't appear to work with recursion (but I admit I still don't fully understand the lib).

Is there anyway to know when a set of task queue tasks (and children that get spawned recursively) are completed so I can finalize my blob and do whatever with it?

Thanks,John

解决方案

All right, so here's what I did. I had to modify Mitch's solution just a bit, but he definitely got me in the right direction with the advice to return the future value instead of an immediate one.

I had to create an intermidate DummyJob that takes the output of the recursion

   public static class DummyJob extends Job1<Void, List<Void>> {
      @Override
      public Value<Void> run(List<Void> dummies) {
         return null;
      }
   }

Then, I submit the output of the DummyJob to the Blob Finalizer in a waitFor

List<FutureValue<Void>> dummies = new ArrayList<FutureValue<Void>>();
for (Interval in : ins) {
   dummies.add(futureCall(new DataFetcher(), immediate(file), immediate(in.getStart()),
         immediate(in.getEnd())));
}

FutureValue<Void> fv = futureCall(new DummyJob(), futureList(dummies));

return futureCall(new DataWriter(), immediate(file), waitFor(fv));

Thank you Mitch and Nick!!

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