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POBug in parallel tree printing method
 

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  1. POBug in parallel tree printing method
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    <p>Classes:</p> <pre><code>public class Tree { public Node RootNode { get; set; } } public class Node { public int Key { get; set; } public object Value { get; set; } public Node ParentNode { get; set; } public List&lt;Node&gt; Nodes { get; set; } } </code></pre> <p>Methods:</p> <p>This method generates a tree.</p> <pre><code>private static int totalNodes = 0; static Tree GenerateTree() { Tree t = new Tree(); t.RootNode = new Node(); t.RootNode.Key = 0; t.RootNode.Nodes = new List&lt;Node&gt;(); Console.WriteLine(t.RootNode.Key); List&lt;Node&gt; rootNodes = new List&lt;Node&gt;(); rootNodes.Add(t.RootNode); while (totalNodes &lt;= 100000) { List&lt;Node&gt; newRootNodes = new List&lt;Node&gt;(); foreach (var rootNode in rootNodes) { for (int j = 0; j &lt; 3; j++) { totalNodes++; Console.Write(string.Format(" {0}({1}) ", totalNodes, rootNode.Key)); Node childNode = new Node() {Key = totalNodes, Nodes = new List&lt;Node&gt;(), ParentNode = t.RootNode}; rootNode.Nodes.Add(childNode); newRootNodes.Add(childNode); } Console.Write(" "); } Console.WriteLine(); rootNodes = newRootNodes; } return t; } </code></pre> <p>This method is supposed to print a tree, but node is null in some case:</p> <pre><code> static void PrintTreeParallel(Node rootNode) { List&lt;Node&gt; rootNodes = new List&lt;Node&gt;(); List&lt;Node&gt; newRootNodes = new List&lt;Node&gt;(); rootNodes.Add(rootNode); Console.WriteLine(rootNode.Key); while (rootNodes.Count &gt; 0) { newRootNodes = new List&lt;Node&gt;(); Parallel.ForEach(rootNodes, node =&gt; { if (node != null) { Console.Write(string.Format(" {0} ", node.Key)); if (node.Nodes != null) Parallel.ForEach(node.Nodes, newRoot =&gt; { newRootNodes.Add(newRoot); }); } else { //HOW CAN WE GET HERE????? Debugger.Break(); Console.WriteLine(rootNodes.Count); } }); Console.WriteLine(); rootNodes = newRootNodes; } } </code></pre> <p>Execute:</p> <pre><code> static void Main(string[] args) { var t = GenerateTree(); Console.WriteLine("Tree generated"); PrintTreeParallel(t.RootNode); Console.WriteLine("Tree printed paral"); Console.ReadLine(); } </code></pre> <p>Question:</p> <p><strong>What's wrong here?</strong> Why node is null in some case? And it happens only when there are a lot of generated nodes. For ex if there would be only 10 nodes everything is OK.</p>
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    1. This table or related slice is empty.
    1. PTQuestion
    1. USElastep
    1. USElastep
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    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
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      1. PTAnswer
    2. PO
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    3. PO
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    1. VO
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      1. POBug in parallel tree printing method
      1. USElastep
      1. VTFavorite
    2. VO
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      1. POBug in parallel tree printing method
      1. This table or related slice is empty.
      1. VTUpMod
    1. COList<T> is not threadsafe.
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      1. USJan
    2. COOk, but where's the bug? What happens? Can you, please, explain?
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      1. POBug in parallel tree printing method
      1. USElastep
 

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