(有时)词典中不存在给定的键 [英] (Sometimes) The given key was not present in the dictionary

问题描述

我正在使用下面的代码以list参数启动线程，但有时会引发异常:

I am using the code below to start threads with a list parameter but sometimes it throws an exception:

字典中不存在给定的键

The given key was not present in the dictionary

从此行:

Thread MoveThread = new Thread(() => MoveTask(ControllerDictionary[i]));

如何解决该错误?

完整代码:

var ControllerDictionary = ConfigFile.ControllerList.Select((c, i) => new { Controller = c, Index = i })
    .GroupBy(x => x.Index % AppSettings.SimultaneousProcessNumber)
    .Select((g, i) => new { GroupIndex = i, Group = g })
    .ToDictionary(x => x.GroupIndex, x => x.Group.Select(xx => xx.Controller).ToList());

for (int i = 0; i < ControllerDictionary.Count; i++)
{
     Thread MoveThread = new Thread(() => MoveTask(ControllerDictionary[i]));
     MoveThread.Start();

     foreach (var Controller in ControllerDictionary[i])
         Logger.Write(string.Format("{0} is in move thread {1}.", Controller.Ip, (i + 1)),EventLogEntryType.Information, AppSettings.LogInfoMessages);
}

推荐答案

您正在捕获变量 i，而不是其值.因此，当前您可能有多个线程使用相同的索引调用MoveTask ...，有时i的值可能等于ControllerDictionary.Count.

You're capturing the variable i, rather than its value. So currently you could have several threads calling MoveTask using the same index... and sometimes the value of i could be equal to ControllerDictionary.Count.

如果将i的副本放入循环中的变量中，则可以解决此问题，因为在循环的每次迭代中都会获得一个单独的变量:

If you take a copy of i into a variable within the loop, that fixes the problem as you'll get a separate variable on each iteration of the loop:

for (int i = 0; i < ControllerDictionary.Count; i++)
{
    int index = i;
    Thread MoveThread = new Thread(() => MoveTask(ControllerDictionary[index]));
    ... 
}

甚至更好的是，从线程中完全提取ControllerDictionary提取:

Or even better, extract the ControllerDictionary fetch from the thread entirely:

for (int i = 0; i < ControllerDictionary.Count; i++)
{
    var value = ControllerDictionary[i];
    Thread MoveThread = new Thread(() => MoveTask(value));
    ... 
}

此外，还不清楚为什么要使用字典.既然您知道键都在[0, count)范围内，为什么不只使用数组呢?您可以将查询更改为:

Additionally, it's not really clear why you're using a dictionary at all. Given that you know the keys will all be in the range [0, count) why don't you just use an array? You'd change your query to:

var controllerLists = ConfigFile.ControllerList
    .Select((c, i) => new { Controller = c, Index = i })
    .GroupBy(x => x.Index % AppSettings.SimultaneousProcessNumber)
    .Select(g => g.Select(xx => xx.Controller).ToList())
    .ToArray();

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