为什么用Regex.IsMatch检查此字符串会导致CPU达到100％? [英] Why does checking this string with Regex.IsMatch cause CPU to reach 100%?

问题描述

在特定字符串上使用 Regex.IsMatch (C#、. Net 4.5)时，CPU达到100％.

When using Regex.IsMatch (C#, .Net 4.5) on a specific string, the CPU reaches 100%.

字符串:

https://www.facebook.com/CashKingPirates/photos/a.197028616990372.62904.196982426994991/1186500984709792/?type=1&permPage=1

模式:

^http(s)?://([\w-]+.)+[\w-]+(/[\w- ./?%&=])?$

完整代码:

Regex.IsMatch("https://www.facebook.com/CashKingPirates/photos/a.197028616990372.62904.196982426994991/1186500984709792/?type=1&permPage=1",
                @"^http(s)?://([\w-]+.)+[\w-]+(/[\w- ./?%&=])?$");

我发现编辑URL可以防止此问题.修改后的网址:

I found that redacting the URL prevents this problem. Redacted URL:

https://www.facebook.com/CashKingPirates/photos/a.197028616990372.62904.196982426994991/1186500984709792

但是仍然非常有兴趣了解导致这种情况的原因.

But still very interested in understanding what causes this.

推荐答案

正如nu11p01n73R指出的那样，您使用正则表达式进行了大量回溯.这是因为表达式的各个部分都可以匹配相同的事物，这使引擎在找到结果之前必须尝试许多选择.

As nu11p01n73R pointed out, you have a lot backtracking with your regular expression. That’s because parts of your expression can all match the same thing, which gives the engine many choices it has to try before finding a result.

您可以通过更改正则表达式以使各个节更具体来避免这种情况.在您的情况下，原因是您想匹配一个真实的点，但使用了所有匹配字符..您应该将其转义为 \..

You can avoid this by changing the regular expression to make individual sections more specific. In your case, the cause is that you wanted to match a real dot but used the match-all character . instead. You should escape that to \..

这应该已经大大减少了回溯的需要并使其快速:

This should already reduce the backtracking need a lot and make it fast:

^http(s)?://([\w-]+\.)+[\w-]+(/[\w- ./?%&=])?$

如果要实际匹配原始字符串，则需要在字符类的末尾添加一个量词:

And if you want to actually match the original string, you need to add a quantifier to the character class at the end:

^http(s)?://([\w-]+\.)+[\w-]+(/[\w- ./?%&=]+)?$
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