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fix race condition for test MulticlassTreeFeaturizedLRTest #4950

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Merged
frank-dong-ms-zz merged 3 commits into from
Mar 18, 2020
Merged

fix race condition for test MulticlassTreeFeaturizedLRTest #4950

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d2e0b1e
fix race condition for test MulticlassTreeFeaturizedLRTest
frank-dong-ms-zz Mar 18, 2020
4a84d18
add necessary comments
frank-dong-ms-zz Mar 18, 2020
5780a31
enhance comments
frank-dong-ms-zz Mar 18, 2020
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9 changes: 8 additions & 1 deletion src/Microsoft.ML.FastTree/TreeEnsembleFeaturizer.cs
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Expand Up @@ -735,14 +735,17 @@ private static IDataView AppendFloatMapper<TInput>(IHostEnvironment env, IChanne
bool identity;
var converter = Conversions.Instance.GetStandardConversion<TInput, ulong>(type, dstType, out identity);
var isNa = Conversions.Instance.GetIsNAPredicate<TInput>(type);
ulong temp = 0;

ValueMapper<TInput, Single> mapper;
if (seed == 0)
{
mapper =
(in TInput src, ref Single dst) =>
{
//Attention: This method is called from multiple threads.
//Do not move the temp variable outside this method.
//If you do, the variable is shared between the threads and results in a race condition.
ulong temp = 0;
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@harishsk harishsk Mar 18, 2020 •
edited by frank-dong-ms-zz
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Very nice find! :-) Can you please add some comments about this change? Otherwise some future developer might want to "optimize" this and move it back.

Also, this pattern deserves more investigation. Do we have other mappers that are using variables set outside the mapper function definition? #Resolved

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@frank-dong-ms-zz frank-dong-ms-zz Mar 18, 2020

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Yes, sure, I will add comments on this.

In reply to: 394130751 [](ancestors = 394130751)

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@frank-dong-ms-zz frank-dong-ms-zz Mar 18, 2020

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@sharwell do you have any tool recommendation to detect similar race condition issue either static code analyze or run time detection?

In reply to: 394131983 [](ancestors = 394131983,394130751)

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@frank-dong-ms-zz frank-dong-ms-zz Mar 18, 2020

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No similar issue found from other mappers but mapper are not only function used in multi-threading condition and it is impossible to view for all similar issue.

In reply to: 394130751 [](ancestors = 394130751)

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@sharwell sharwell Mar 18, 2020 •
edited by frank-dong-ms-zz
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I'm not aware of such a tool. It would be easier to write a more targeted tool that identified variables captured by a lambda so they could be reviewed for cases like this. #Resolved

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@frank-dong-ms-zz frank-dong-ms-zz Mar 18, 2020

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Got it, thanks

In reply to: 394334398 [](ancestors = 394334398)

if (isNa(in src))
{
dst = Single.NaN;
Expand All @@ -759,6 +762,10 @@ private static IDataView AppendFloatMapper<TInput>(IHostEnvironment env, IChanne
mapper =
(in TInput src, ref Single dst) =>
{
//Attention: This method is called from multiple threads.
//Do not move the temp variable outside this method.
//If you do, the variable is shared between the threads and results in a race condition.
ulong temp = 0;
if (isNa(in src))
{
dst = Single.NaN;
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