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Reduce ImmutableDictionary allocations in CreateCompilationTrackerMap #70319

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merged 3 commits into from
Oct 12, 2023
Merged

Reduce ImmutableDictionary allocations in CreateCompilationTrackerMap #70319

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77b4ead
Reduce ImmutableDictionary allocations in CreateCompilationTrackerMap
ToddGrun Oct 10, 2023
2ac7cd4
Use ArrayBuilder instead of allocating a new list each time
ToddGrun Oct 10, 2023
fe911b1
Forgot to add the using around the ArrayBuilder call
ToddGrun Oct 10, 2023
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21 changes: 18 additions & 3 deletions src/Workspaces/Core/Portable/Workspace/Solution/SolutionState.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1549,12 +1549,27 @@ private static ProjectDependencyGraph CreateDependencyGraph(

private ImmutableDictionary<ProjectId, ICompilationTracker> CreateCompilationTrackerMap(ProjectId changedProjectId, ProjectDependencyGraph dependencyGraph)
{
var builder = ImmutableDictionary.CreateBuilder<ProjectId, ICompilationTracker>();
if (_projectIdToTrackerMap.Count == 0)
return _projectIdToTrackerMap;

using var _ = ArrayBuilder<KeyValuePair<ProjectId, ICompilationTracker>>.GetInstance(_projectIdToTrackerMap.Count, out var newTrackerInfo);
var allReused = true;
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@jasonmalinowski jasonmalinowski Oct 10, 2023 •
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Are we better off just doing a loop first checking the dependency graph CanReuse() for each of the entries, and if so just bailing entirely? Otherwise here we're still allocating the builder only to throw it away if that case happens.

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From what I've seen, pretty much everything about ImmutableDictionarys are slow, so I figured it was just better to make a single pass through it. The intent here is that the ArrayBuilder won't actually allocate normally, so the only real allocation that will happen is if the ImmutableDictionary really needs to be created.

foreach (var (id, tracker) in _projectIdToTrackerMap)
builder.Add(id, CanReuse(id) ? tracker : tracker.Fork(tracker.ProjectState, translate: null));
{
var localTracker = tracker;
if (!CanReuse(id))
{
localTracker = tracker.Fork(tracker.ProjectState, translate: null);
allReused = false;
}

return builder.ToImmutable();
newTrackerInfo.Add(new KeyValuePair<ProjectId, ICompilationTracker>(id, localTracker));
}

if (allReused)
return _projectIdToTrackerMap;

return ImmutableDictionary.CreateRange(newTrackerInfo);

// Returns true if 'tracker' can be reused for project 'id'
bool CanReuse(ProjectId id)
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