父任务不会等待子任务完成 [英] Parent task does not wait for child task to complete

问题描述

因此​​，这里是我的code

 任务＆LT; INT [] GT;父= Task.Run（（）=＆GT;
{
    变种结果=新INT [3];

    TaskFactory TF =新TaskFactory（TaskCreationOptions.AttachedToParent，TaskContinuationOptions.ExecuteSynchronously）;

    的for（int i = 0; I＆LT; result.Length;我++）
    {
        INT J =;
        tf.StartNew（（）=＆GT;结果[J] = getRandomNumber的（J））;
    }

    返回结果;
}）;

VAR finalTask​​ = parent.ContinueWith（parentTask =＆GT;
{
    的foreach（在parentTask.Result变种I）
    {
        Console.WriteLine（ⅰ）;
    }
}）;

finalTask​​.Wait（）;
 

基本上我创建3 工作■哪些是工作称为父（我猜）的儿童。我excpect父任务等待所有三个子任务来完成。在此之后， finalTask​​ 将等待，因为 finalTask​​.Wait（执行）; 此statemant。但事情并没有发生预期。我的意思是在应用程序退出之前，任何 getRandomNumber的的要求完成。的code。在这里有些部分是从书里面说，这些家长的任务应该等待子任务来完成，这显然是没有发生复制。我失去了一些东西呢？

这是什么getRandomNumber的呢

 公共静态INT getRandomNumber的（INT二）
{
    随机兰特=新的随机（）;

    的for（int i = 0; I＆LT; 10亿;我++）{} //模仿一些工作

    返回rand.Next（1000）;
}
 

这code做同样的事情

 任务＆LT; INT [] GT;父= Task.Run（（）=＆GT;
{
    变种结果=新INT [3];

    的for（int i = 0; I＆LT; result.Length;我++）
    {
        INT J =;
        新的任务（（）=＆GT;结果[J] = getRandomNumber的（J），TaskCreationOptions.AttachedToParent）。开始（）;
    }

    返回结果;
}）;
 

解决方案

此行​​为是由于您使用的 Task.Run 的方法，即禁止儿童工作被附加到父：

  

在运行法是一种简单的替代方式的<一个href="http://msdn.microsoft.com/en-us/library/system.threading.tasks.taskfactory.startnew%28v=vs.110%29.aspx"><$c$c>StartNew方法。它创建了一个任务[其] <一个href="http://msdn.microsoft.com/en-us/library/system.threading.tasks.task.creationoptions%28v=vs.110%29.aspx"><$c$c>CreationOptions属性值是<一个href="http://msdn.microsoft.com/en-us/library/system.threading.tasks.taskcreationoptions%28v=vs.110%29.aspx"><$c$c>TaskCreationOptions.DenyChildAttach.

要解决，只需从

改变你的第一线

 任务＆LT; INT [] GT;父= Task.Run（（）=＆GT;
 

到

 任务＆LT; INT [] GT;父= Task.Factory.StartNew（（）=＆GT;
 

So here is my code

Task<int[]> parent = Task.Run(() =>
{
    var result = new int[3];

    TaskFactory tf = new TaskFactory(TaskCreationOptions.AttachedToParent, TaskContinuationOptions.ExecuteSynchronously);

    for (int i = 0; i < result.Length; i++)
    {
        int j = i;
        tf.StartNew(() => result[j] = GetRandomNumber(j));
    }

    return result;
});

var finalTask = parent.ContinueWith(parentTask =>
{
    foreach (var i in parentTask.Result)
    {
        Console.WriteLine(i);   
    }
});

finalTask.Wait();

Basically I create 3 Tasks which are children of Task called parent (I guess). I excpect parent task to wait for all three child tasks to complete. After that the finalTask would be waited to execute because of finalTask.Wait(); this statemant. But things do not happen as expected. I mean the application exits before the any of GetRandomNumber calls finishes. Some part of the code in here is copied from book which stated that those parent task should wait for child task to complete which apparently is not happening. Am I missing something here ?

this is what GetRandomNumber does

public static int GetRandomNumber(int ii)
{
    Random rand = new Random();

    for (int i = 0; i < 1000000000; i++) { } // imitate some jobs

    return rand.Next(1000);
}

This code does the same thing

Task<int[]> parent = Task.Run(() =>
{
    var result = new int[3];

    for (int i = 0; i < result.Length; i++)
    {
        int j = i;
        new Task(() => result[j] = GetRandomNumber(j), TaskCreationOptions.AttachedToParent).Start();
    }

    return result;
});

解决方案

This behaviour is due to your use of the Task.Run method, which forbids child tasks from being attached to the parent:

The Run method is a simpler alternative to the StartNew method. It creates a task [whose] CreationOptions property value is TaskCreationOptions.DenyChildAttach.

To resolve, simply change your first line from

Task<int[]> parent = Task.Run(() =>

to

Task<int[]> parent = Task.Factory.StartNew(() =>

这篇关于父任务不会等待子任务完成的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！