blocks|key|971103|text|如果您认为sum+%2B=+ComplicatedFunction实际上是由一系列操作组成，那么可以这样说：|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|971104|r1+<-+Load+current+value+of+sum
r2+<-+ComplicatedFunction(...)
r1+<-+r1+%2B+r2|code-block|syntax|javascript|971105|所以现在我们随机交错两个(或更多)并行的实例。一个线程可能持有一个陈旧的sum“旧值”，它用它来执行它的计算，其结果被写回到某个修改后的sum版本之上。这是一个经典的竞争条件，因为根据交织的方式，一些结果会以一种不确定的方式丢失。|971106|entityMap^0|5|Q|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|R|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|S|8|@]|D|@]|E|$]]|$1|M|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|N|$]]

If you think about that <code>sum += ComplicatedFunction</code>as being actually composed of a bunch of operations, say:

<pre><code>r1 &lt;- Load current value of sum
r2 &lt;- ComplicatedFunction(...)
r1 &lt;- r1 + r2
</code></pre>

So now we randomly interleave two (or more) parallel instances of this. One thread may be holding a stale "old value" of sum which it uses to perform its computation, the result of which it writes back over top of some modified version of sum. It's a classic race condition, because some results are getting lost in a nondeterministic way based on how the interleaving is done.

blocks|key|1185531|text|或者，您可以使用.Net中正确定义的并行聚合操作。以下是代码|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1185532|++++++++object+locker+=+new+object();
++++++++double+sum=+0.0;
++++++++Parallel.ForEach(mArray,
++++++++++++++++++++++++()+=>+0.0,+++++++++++++++++//+Initialize+the+local+value.
++++++++++++++++++++++++(i,+state,+localResult)+=>+localResult+%2B+ComplicatedFunction(i),+localTotal+=>+++//+Body+delegate+which+returns+the+new+local+total.+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++//+Add+the+local+value
++++++++++++++++++++++++++++{
++++++++++++++++++++++++++++++++lock+(locker)+sum4%2B=+localTotal;
++++++++++++++++++++++++++++}++++//+to+the+master+value.
++++++++++++++++++++++++);|code-block|syntax|javascript|1185533|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/linq/aggregation-operations^0|8|4|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

Or you can use Parallel Aggregation Operations, as properly defined in <a href="https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/concepts/linq/aggregation-operations" rel="nofollow noreferrer">.Net</a>. Here is the code

<pre><code> object locker = new object();
 double sum= 0.0;
 Parallel.ForEach(mArray,
 () =&gt; 0.0, // Initialize the local value.
 (i, state, localResult) =&gt; localResult + ComplicatedFunction(i), localTotal =&gt; // Body delegate which returns the new local total. // Add the local value
 {
 lock (locker) sum4+= localTotal;
 } // to the master value.
 );
</code></pre>

I have a <code>foreach</code> loop that I am parallelizing and I noticed something odd. The code looks like

<pre><code>double sum = 0.0;

Parallel.ForEach(myCollection, arg =&gt;
{
 sum += ComplicatedFunction(arg);
});

// Use sum variable below
</code></pre>

When I use a regular <code>foreach</code> loop I get different results. There may be something deeper down inside the <code>ComplicatedFunction</code> but it is possible that the <code>sum</code> variable is being unexpectantly affected by the parallelization?

Different summation results with Parallel.ForEach

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我有一个正在并行化的foreach循环，我注意到了一些奇怪的事情。代码看起来像这样double sum = 0.0;Parallel.ForEach(myCollection, arg =>{     sum += ComplicatedFunction(arg);});// Use sum variable belo...

问与Parallel.ForEach的不同求和结果
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