Regex Class Caching Changes between .NET Framework 1.1 and .NET Framework 2.0 [Josh Free]

re: Regex Class Caching Changes between .NET Framework 1.1 and .NET Framework 2.0 [Josh Free]

Nick — Thu, 19 Oct 2006 22:36:32 GMT

Does this also applies when RegexOptions.Compiled is set ? Or are compiled Regex always cached ?

RE: Does this also applies when RegexOptions.Compiled is set ? Or are compiled Regex always cached ?

Josh Free — Thu, 19 Oct 2006 23:24:00 GMT

Nick,

The use of RegexOptions flags does not impact the behavior of the cache. Developers can use the RegexOptions.Compiled flag on either a Regex constructor (to create a Regex instance) or on a static Match method. The Regex object returned from the constructor will not be added to the cache. Remember, the cache does not impact the performance of match operations - it only impacts the performance of regular expression creation.

For instance calling this constructor multiply times will cause the expression to be compiled each time:

Regex r1 = new Regex("abc*", RegexOptions.Compiled);

Regex r2 = new Regex("abc*", RegexOptions.Compiled);

Regex r3 = new Regex("abc*", RegexOptions.Compiled);

However, calling the static method multiple time will use the Regex cache - and subsequent calls may benefit from the cache:

Regex.Match("1234bar", @"(\d*)bar", RegexOptions.Compiled);

For more information on Regex compilation, please refer to the "RegularExpression Compilation" section in the January 2006 edition of MSDN Magazine: http://msdn.microsoft.com/msdnmag/issues/06/01/CLRInsideOut/

re: Regex Class Caching Changes between .NET Framework 1.1 and .NET Framework 2.0 [Josh Free]

nativecpp — Fri, 20 Oct 2006 00:10:03 GMT

Hi Josh,

Thanks for the info. From yr examples, it can be concluded that compiled option is per instance since it compiles 3 times with the same 'abc*', right ?

re: Regex Class Caching Changes between .NET Framework 1.1 and .NET Framework 2.0 [Josh Free]

Kevin Dente — Fri, 20 Oct 2006 00:29:01 GMT

How about the assembly cache used by the XmlSerializer? Has the potential for massive leaks present in 1.1 been addressed in 2.0?

re: Regex Class Caching Changes between .NET Framework 1.1 and .NET Framework 2.0 [Josh Free]

Ratnakar — Fri, 20 Oct 2006 15:41:18 GMT

Can you please comment on the caching and performance of the following piece of Regex code(both for 1.1 and 2.0) where we are using list of patterns in a loop. I doubt any caching is going on here.

string[] allowedFormatsWithTimePattern = new string[] {//list of patterns };

//loop through all the patterns from the array

for(int indx = 0; indx< allowedFormatsWithTimePattern.Length; indx++)

{

Regex r = new Regex(allowedFormatsWithTimePattern[indx], RegexOptions.Compiled);

if(r.IsMatch(toParse))

{

// do something

}

for better performance should we avoid looping as the number of patterns are fairly constant.

re: Regex Class Caching Changes between .NET Framework 1.1 and .NET Framework 2.0 [Josh Free]

Josh Free — Sat, 21 Oct 2006 00:36:43 GMT

Hi Ratnakar,

Yes, you should avoid calling the Regex constructor in the for-loop. Instead of having a string[] of patterns that you use to instantiate Regex objects again and again, why not create the Regex objects just one time, and save them in a Regex[]?

Then you can replace these 2 lines inside your for-loop:

Regex r = new Regex(allowedFormatsWithTimePattern[indx], RegexOptions.Compiled);

if(r.IsMatch(toParse)) { .... }

With this 1 line that uses the Regex[], r:

if(r[indx].IsMatch(toParse)) { .... }

By making this change, you avoid having to compile the regular expression on the fly, each time in the for-loop.

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