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Reduce allocations in TaskExecutionHost #11804

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Reduce allocations in TaskExecutionHost #11804

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326071c
Reduce allocations in TaskExecutionHost
Erarndt May 7, 2025
cf381f3
Update TaskExecutionHost.cs
SimaTian May 9, 2025
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22 changes: 20 additions & 2 deletions src/Build/BackEnd/TaskExecutionHost/TaskExecutionHost.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,7 @@

using TaskItem = Microsoft.Build.Execution.ProjectItemInstance.TaskItem;
using Task = System.Threading.Tasks.Task;
using Microsoft.Build.Collections;

#nullable disable

Expand Down Expand Up @@ -1423,9 +1424,26 @@ private void GatherTaskItemOutputs(bool outputTargetIsItem, string outputTargetN

static IEnumerable<KeyValuePair<string, string>> EnumerateMetadata(IDictionary customMetadata)
{
foreach (DictionaryEntry de in customMetadata)
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@SimaTian SimaTian May 9, 2025 •
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What is the penalty for using the interface here please? Is it boxing in this case or something else?
(e.g. from what I read, we use specialized iterations based on type, so I assume there is something to be gained, hence the boxing question)

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The goal here is to avoid boxing the struct enumerator of these collections. In sufficiently hot paths, the allocations can really add up.

if (customMetadata is CopyOnWriteDictionary<string> copyOnWriteDictionary)
{
yield return new KeyValuePair<string, string>((string)de.Key, EscapingUtilities.Escape((string)de.Value));
foreach (KeyValuePair<string, string> kvp in copyOnWriteDictionary)
{
yield return new KeyValuePair<string, string>(kvp.Key, EscapingUtilities.Escape(kvp.Value));
}
}
else if (customMetadata is Dictionary<string, string> dictionary)
{
foreach (KeyValuePair<string, string> kvp in dictionary)
{
yield return new KeyValuePair<string, string>(kvp.Key, EscapingUtilities.Escape(kvp.Value));
}
}
else
{
foreach (DictionaryEntry de in customMetadata)
{
yield return new KeyValuePair<string, string>((string)de.Key, EscapingUtilities.Escape((string)de.Value));
}
}
}
}
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