WIP - Fix performance and memory allocation issues in ReadPdhMultiString.#5845
WIP - Fix performance and memory allocation issues in ReadPdhMultiString.#5845jcarino wants to merge 1 commit into
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@jcarino We can not merge the contribution until you sign CLA. |
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Ah, |
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CLA has now been signed. |
| char nextChar = (char)next4; | ||
| if (nextChar == '\0') | ||
| { | ||
| strColl.Add(sb.ToString()); |
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Adding to strColl should occur outside the while loop. The updated logic causes the contents of sb to be dropped on the floor by the break statement when next4 == 0.
Essentially, replace the original allSubstringsWithNulls += (char)next4 statement with sb.Append(nextChar) and move the strColl.Add statement to the original location after the while loop.
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You're right, but adding to strColl only outside the while loop has some memory implications (has to alloc at least one extra string before Split). Can we just add another strColl.Add(sb.ToString()); outside the while to catch whatever is left in sb?
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@dantraMSFT Please clarify - this file is excluded from compilation - is it acceptable to change it without tests? And will we use it later? |
@iSazonov Thanks for bringing it up :) You are right that we don't have a way to officially validate the changes. @TravisEz13, any thoughts? For background: the perf counter cmdlets are disabled due to unsupported APIs. But the files are left in place so that
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We should not make changes that are not tested. I think we can postpone this change until the API is ported in the future. I've seen that CoreFX team still doesn't have a consensus how to do it. Also if we decide to use Windows Compatibility Pack and it will support this API, then we could also include this in the compilation. |
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Not only is it not tested. The file is not being compiled. I don't think we can take any changes to this file except possibly adding a comment to this effect and pointing to the issue to add the CmdLets back using supported APIs. #4306 |
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I think we should close the PR until we compile this code again. |
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@jcarino The consensus is that we cannot take changes to this code at this time. |
PR Summary
String concats in ReadPdhMultiString have been replaced with a StringBuilder to significantly reduce heap allocation and GC.
ReadPdhMultiString reads characters one by one from a pointer location into a string, then splits that string into a string collection (on the null character '\0'). However, it does this through a looped string concat, allocating a new string on the heap for each character read in. This has significant GC implications for large strings. The string concats have been replaced with a string builder, and the strings are split and added to the StringCollection on the fly.
PR Checklist
Note: Please mark anything not applicable to this PR
NA.WIP:to the beginning of the title and remove the prefix when the PR is ready.