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Avoid using regex when unnecessary in ScriptWriter #18348

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merged 5 commits into from Oct 26, 2022
Merged

Avoid using regex when unnecessary in ScriptWriter #18348

merged 5 commits into from Oct 26, 2022

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daxian-dbw
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@daxian-dbw daxian-dbw commented Oct 21, 2022 •
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PR Summary

The Regex.IsMatch in GetDotNetType is pretty expensive. Actually, in most cases, we can use simpler checks to get what we need. Handle those common cases so as to avoid regular expression checks when possible.

PR Context

It's reported from MS internal team the GetDotNetType method call results in tons of regular expression creations, taking up a lot of CPU usage.

PR Checklist

@daxian-dbw daxian-dbw closed this Oct 21, 2022
@daxian-dbw daxian-dbw reopened this Oct 21, 2022
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This PR has 26 quantified lines of changes. In general, a change size of upto 200 lines is ideal for the best PR experience!

Quantification details 

Label      : Extra Small
Size       : +19 -7
Percentile : 10.4%

Total files changed: 1

Change summary by file extension:
.cs : +19 -7

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iSazonov
iSazonov reviewed Oct 26, 2022
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src/System.Management.Automation/cimSupport/cmdletization/ScriptWriter.cs
// Now we have to fall back to the expensive regular expression matching, because 'PSType'
// could be a composite type like 'Nullable<enum_name>' or 'Dictionary<enum_name, object>',
// but we don't want the case where the enum name is part of another type's name.
matchFound = Regex.IsMatch(psType, $@"\b{Regex.Escape(e.EnumName)}\b");
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nit: we could build single regex pattern as enumName1 | enumName2 | ... | enumName№ - I believe one Regex is more faster than many. I mean we build the pattern in the loop and move the Regex out the loop.

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Yeah, it could reduce the number of regex's created for the match, which would help a lot if regex matching were a must-have.

In this case, the common cases handled above will cover nearly all scenarios practically, so I think we just keep it simple when it comes to regex matching.

@daxian-dbw daxian-dbw merged commit 8b82fa3 into PowerShell:master Oct 26, 2022
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@daxian-dbw daxian-dbw deleted the regex branch October 26, 2022 16:50
@daxian-dbw daxian-dbw assigned daxian-dbw and unassigned TravisEz13 Oct 26, 2022
@daxian-dbw daxian-dbw added CL-General Indicates that a PR should be marked as a general cmdlet change in the Change Log CL-Performance Indicates that a PR should be marked as a performance improvement in the Change Log and removed CL-General Indicates that a PR should be marked as a general cmdlet change in the Change Log labels Oct 26, 2022
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