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    <p>If you can post the email that's causing the problem (perhaps anonymized in some way), that will give us more information, but I'm <em>thinking</em> the problem is this little guy right here:</p> <pre><code>([-.]\\w+)*\\.\\w+([-.]\\w+)* </code></pre> <p>To understand the problem, let's break that into groups:</p> <pre><code>([-.]\\w+)* \\.\\w+ ([-.]\\w+)* </code></pre> <p>The strings that will match <code>\\.\\w+</code> are a <strong>subset</strong> of those that will match <code>[-.]\\w+</code>. So if part of your input looks like <code>foo.bar.baz.blah.yadda.com</code>, your regex engine has no way of knowing which group is supposed to match it. Does that make sense? So the first <code>([-.]\\w+)*</code> could match <code>.bar.baz.blah</code>, then the <code>\\.\\w+</code> could match <code>.yadda</code>, then the last <code>([-.]\\w+)*</code> could match <code>.com</code>...</p> <p>...<strong>OR</strong> the first clause could match <code>.bar.baz</code>, the second could match <code>.blah</code>, and the last could match <code>.yadda.com</code>. Since it doesn't know which one is right, it will keep trying different combinations. It should stop eventually, but that could still take a long time. This is called "catastrophic backtracking".</p> <p>This issue is compounded by the fact that you're using <a href="http://www.regular-expressions.info/brackets.html" rel="nofollow">capturing groups</a> rather than non-capturing groups; i.e. <code>([-+.]\\w+)</code> instead of <code>(?:[-+.]\\w+)</code>. That causes the engine to try and separate and save whatever matches inside the parentheses for later reference. But as I explained above, it's ambiguous which group each substring belongs in.</p> <p>You might consider replacing everything after the @ with something like this:</p> <pre><code>\\w[-\\w]*\\.[-.\\w]+ </code></pre> <p>That could use some refinement to make it more specific, but you get the general idea. Hope I explained all this well enough; grouping and backreferences are kind of tough to describe.</p> <h3>EDIT:</h3> <p>Looking back at your pattern, there's a deeper issue here, still related to the backtracking/ambiguity problem I mentioned. The clause <code>\\w+([-.]\\w+)*</code> is ambiguous all by itself. Splitting it into parts, we have:</p> <pre><code>\\w+ ([-.]\\w+)* </code></pre> <p>Suppose you have a string like <code>foobar</code>. Where does the <code>\\w+</code> end and the <code>([-.]\\w+)*</code> begin? How many repetitions of <code>([-.]\\w+)</code> are there? Any of the following could work as matches:</p> <pre><code>f(oobar) foo(bar) f(o)(oba)(r) f(o)(o)(b)(a)(r) foobar etc... </code></pre> <p>The regex engine doesn't know which is important, so it will try them all. This is the same problem I pointed out above, but it means you have it in multiple places in your pattern. </p> <p>Even worse, <code>([-.]\\w+)*</code> is <em>also</em> ambiguous, because of the <code>+</code> after the <code>\\w</code>. How many groups are there in <code>blah</code>? I count 16 possible combinations: <code>(blah)</code>, <code>(b)(lah)</code>, <code>(bl)(ah)</code>...</p> <p>The amount of different possible combinations is going to be huge, even for a relatively small input, so your engine is going to be in overdrive. I would definitely simplify it if I were you. </p>
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    1. PORegex MatchCollection obj hangs\"Function evuluation timed out" after Regex.Matches
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    1. USJustin Morgan
    1. USJustin Morgan
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    1. COThanks, will try too change that. Regarding which email causing the problem, I can't see that. The MatchCollection objects members isn't "acceessible". And I tried different patterns(see update in my post), and all seems to hang... "catastrophic backtracking":D
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      1. USJohan Helsén
    2. CO@Johan Helsén - Looking at the source code of that page, I see six email addresses. I suspect that if you tried *any* page with six email addresses in it, the program would hang because of the resource intensity of your regex. By the way, see my edit.
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    3. COThanks for your explanation. As you notice by viewing the regex I have, I have alot to learn.
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