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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.
using System.Collections.Immutable;
using System.Threading;
using System.Threading.Tasks;
using Microsoft.CodeAnalysis.Host;
using Microsoft.CodeAnalysis.Host.Mef;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Roslyn.Utilities;
namespace Microsoft.CodeAnalysis.SemanticModelReuse;
internal readonly struct SemanticModelReuseInfo(SemanticModel previousNonSpeculativeSemanticModel, SemanticModel currentSemanticModel, SyntaxNode bodyNode, VersionStamp topLevelSementicVersion)
{
/// <summary>
/// The original <em>non-speculative</em> semantic model we retrieved for this document at some point.
/// </summary>
public readonly SemanticModel PreviousNonSpeculativeSemanticModel = previousNonSpeculativeSemanticModel;
/// <summary>
/// The current semantic model we retrieved <see cref="SemanticModel"/> for the <see cref="BodyNode"/>. Could
/// be speculative or non-speculative.
/// </summary>
public readonly SemanticModel CurrentSemanticModel = currentSemanticModel;
/// <summary>
/// The current method body we retrieved the <see cref="CurrentSemanticModel"/> for.
/// </summary>
public readonly SyntaxNode BodyNode = bodyNode;
/// <summary>
/// The top level version of the project when we retrieved <see cref="SemanticModel"/>. As long as this is the
/// same we can continue getting speculative models to use.
/// </summary>
public readonly VersionStamp TopLevelSemanticVersion = topLevelSementicVersion;
}
internal partial class SemanticModelReuseWorkspaceServiceFactory : IWorkspaceServiceFactory
{
private sealed class SemanticModelReuseWorkspaceService : ISemanticModelReuseWorkspaceService
{
private readonly Workspace _workspace;
/// <summary>
/// A mapping from a document id to the last semantic model we produced for it, along with the top level
/// semantic version that that semantic model corresponds to. We can continue reusing the semantic model as
/// long as no top level changes occur.
/// <para>
/// In general this dictionary will only contain a single key-value pair. However, in the case of linked
/// documents, there will be a key-value pair for each of the independent document links that a document
/// has.
/// </para>
/// <para>
/// A <see langword="null"/> value simply means we haven't cached any information for that particular id.
/// </para>
/// </summary>
private ImmutableDictionary<DocumentId, SemanticModelReuseInfo?> _semanticModelMap = ImmutableDictionary<DocumentId, SemanticModelReuseInfo?>.Empty;
public SemanticModelReuseWorkspaceService(Workspace workspace)
{
_workspace = workspace;
_workspace.WorkspaceChanged += (_, e) =>
{
// if our map points at documents not in the current solution, then we want to clear things out.
// this way we don't hold onto semantic models past, say, the c#/vb solutions closing.
var map = _semanticModelMap;
if (map.IsEmpty)
return;
var solution = e.NewSolution;
foreach (var (docId, _) in map)
{
if (!solution.ContainsDocument(docId))
{
_semanticModelMap = ImmutableDictionary<DocumentId, SemanticModelReuseInfo?>.Empty;
return;
}
}
};
}
public async ValueTask<SemanticModel> ReuseExistingSpeculativeModelAsync(Document document, SyntaxNode node, CancellationToken cancellationToken)
{
var reuseService = document.GetRequiredLanguageService<ISemanticModelReuseLanguageService>();
// See if we're asking about a node actually in a method body. If so, see if we can reuse the
// existing semantic model. If not, return the current semantic model for the file.
var bodyNode = reuseService.TryGetContainingMethodBodyForSpeculation(node);
if (bodyNode == null)
return await document.GetRequiredSemanticModelAsync(cancellationToken).ConfigureAwait(false);
// We were in a method body. Compute the updated map that will contain the appropriate semantic model
// for this document.
//
// In terms of concurrency we the map so that we can operate on it independently of other threads. When
// we compute the final map, we'll grab the semantic model out of it to return (which must be correct
// since we're the thread that created that map). Then, we overwrite the instance map with our final
// map. This map may be stomped on by another thread, but that's fine. We don't have any sort of
// ordering requirement. We just want someone to win and place the new map so that it's there for the
// next caller (which is likely to use the same body node).
var originalMap = _semanticModelMap;
// If we already have a cached *real* semantic model for this body, then just provide that. Note: this
// is also a requirement as you cannot speculate on a semantic model using a node from that same
// semantic model.
if (originalMap.TryGetValue(document.Id, out var reuseInfoOpt) &&
reuseInfoOpt.HasValue &&
reuseInfoOpt.Value.PreviousNonSpeculativeSemanticModel.SyntaxTree == bodyNode.SyntaxTree)
{
return reuseInfoOpt.Value.PreviousNonSpeculativeSemanticModel;
}
var updatedMap = await ComputeUpdatedMapAsync(originalMap, document, bodyNode, cancellationToken).ConfigureAwait(false);
// Grab the resultant semantic model and then overwrite the existing map. We return the semantic model
// from the map *we* computed so that we're isolated from other threads writing to the map stored in the
// field.
var info = updatedMap[document.Id]!.Value;
var semanticModel = info.CurrentSemanticModel;
Interlocked.CompareExchange(ref _semanticModelMap, updatedMap, originalMap);
return semanticModel;
}
private static async Task<ImmutableDictionary<DocumentId, SemanticModelReuseInfo?>> ComputeUpdatedMapAsync(
ImmutableDictionary<DocumentId, SemanticModelReuseInfo?> map, Document document, SyntaxNode bodyNode, CancellationToken cancellationToken)
{
var linkedIds = document.GetLinkedDocumentIds();
// Get the current top level version for this document's project. If it has changed, then we cannot
// reuse any existing cached data for it. This also ensures that we can do things like find the same
// method body node prior to an edit just by counting it's top-level index in the file.
var topLevelSemanticVersion = await document.Project.GetDependentSemanticVersionAsync(cancellationToken).ConfigureAwait(false);
// If we are able to reuse a semantic model, then ensure that this is now the semantic model we're now
// pointing at for this document.
var reuseInfo = await TryReuseCachedSemanticModelAsync(
map, document, bodyNode, topLevelSemanticVersion, cancellationToken).ConfigureAwait(false);
if (reuseInfo != null)
return map.SetItem(document.Id, reuseInfo.Value);
// Otherwise, we couldn't reuse that doc's cached info. Create a fresh map with that doc's real
// semantic model value in it. Note: we still reuse the values stored with the other links for that
// doc as they may still be valid to use.
var semanticModel = await document.GetRequiredSemanticModelAsync(cancellationToken).ConfigureAwait(false);
var builder = ImmutableDictionary.CreateBuilder<DocumentId, SemanticModelReuseInfo?>();
// Note: we are intentionally storing the semantic model instance in the speculative location as well.
builder.Add(document.Id, new SemanticModelReuseInfo(semanticModel, semanticModel, bodyNode, topLevelSemanticVersion));
foreach (var linkedId in linkedIds)
{
// Reuse the existing cached data for any links we have as well
var linkedReuseInfo = map.TryGetValue(linkedId, out var info) ? info : null;
builder.Add(linkedId, linkedReuseInfo);
}
return builder.ToImmutable();
}
private static async Task<SemanticModelReuseInfo?> TryReuseCachedSemanticModelAsync(
ImmutableDictionary<DocumentId, SemanticModelReuseInfo?> map,
Document document,
SyntaxNode bodyNode,
VersionStamp topLevelSemanticVersion,
CancellationToken cancellationToken)
{
// if this is asking about a doc we don't know about, we can't reuse anything.
if (!map.ContainsKey(document.Id))
return null;
// see if this doc matches the docs we're caching information for.
if (!map.TryGetValue(document.Id, out var reuseInfoOpt) || !reuseInfoOpt.HasValue)
return null;
var reuseInfo = reuseInfoOpt.Value;
// can only reuse the cache if nothing top level changed.
if (reuseInfo.TopLevelSemanticVersion != topLevelSemanticVersion)
return null;
// If multiple callers are asking for the exact same body, they can share the exact same semantic model.
// This is valuable when several clients (like completion providers) get called at the same time on the
// same method body edit.
if (reuseInfo.BodyNode == bodyNode)
return reuseInfo;
var reuseService = document.GetRequiredLanguageService<ISemanticModelReuseLanguageService>();
var semanticModel = await reuseService.TryGetSpeculativeSemanticModelAsync(reuseInfo.PreviousNonSpeculativeSemanticModel, bodyNode, cancellationToken).ConfigureAwait(false);
if (semanticModel == null)
return null;
return new SemanticModelReuseInfo(reuseInfo.PreviousNonSpeculativeSemanticModel, semanticModel, bodyNode, topLevelSemanticVersion);
}
}
}
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