Reduce memory usage by caching git objects

Author: Pascal van Buijtene

src/GitVersion.LibGit2Sharp/Git/Branch.cs

@@ -10,16 +10,18 @@ internal sealed class Branch : IBranch
 
     private readonly LibGit2Sharp.Branch innerBranch;
 
-    internal Branch(LibGit2Sharp.Branch branch, LibGit2Sharp.Diff diff)
+    internal Branch(LibGit2Sharp.Branch branch, LibGit2Sharp.Diff diff, GitRepository repo)
     {
+        diff.NotNull();
+        repo.NotNull();
         this.innerBranch = branch.NotNull();
         Name = new(branch.CanonicalName);
 
         var commit = this.innerBranch.Tip;
-        Tip = commit is null ? null : new Commit(commit, diff);
+        Tip = commit is null ? null : repo.GetOrCreate(commit, diff);
 
         var commits = this.innerBranch.Commits;
-        Commits = new CommitCollection(commits, diff);
+        Commits = new CommitCollection(commits, diff, repo);
     }
 
     public ReferenceName Name { get; }

src/GitVersion.LibGit2Sharp/Git/BranchCollection.cs

@@ -8,12 +8,14 @@ internal sealed class BranchCollection : IBranchCollection
     private readonly LibGit2Sharp.BranchCollection innerCollection;
     private readonly Lazy<IReadOnlyCollection<IBranch>> branches;
     private readonly Diff diff;
+    private readonly GitRepository repo;
 
-    internal BranchCollection(LibGit2Sharp.BranchCollection collection, Diff diff)
+    internal BranchCollection(LibGit2Sharp.BranchCollection collection, Diff diff, GitRepository repo)
     {
         this.innerCollection = collection.NotNull();
-        this.branches = new Lazy<IReadOnlyCollection<IBranch>>(() => [.. this.innerCollection.Select(branch => new Branch(branch, diff))]);
+        this.branches = new Lazy<IReadOnlyCollection<IBranch>>(() => [.. this.innerCollection.Select(branch => repo.GetOrCreate(branch, diff))]);
         this.diff = diff.NotNull();
+        this.repo = repo.NotNull();
     }
 
     public IEnumerator<IBranch> GetEnumerator()
@@ -27,7 +29,7 @@ public IBranch? this[string name]
         {
             name = name.NotNull();
             var branch = this.innerCollection[name];
-            return branch is null ? null : new Branch(branch, this.diff);
+            return branch is null ? null : this.repo.GetOrCreate(branch, this.diff);
         }
     }
 

src/GitVersion.LibGit2Sharp/Git/Commit.cs

@@ -14,10 +14,12 @@ internal sealed class Commit : GitObject, ICommit
     private readonly LibGit2Sharp.Commit innerCommit;
     private readonly LibGit2Sharp.Diff repoDiff;
 
-    internal Commit(LibGit2Sharp.Commit innerCommit, LibGit2Sharp.Diff repoDiff) : base(innerCommit)
+    internal Commit(LibGit2Sharp.Commit innerCommit, LibGit2Sharp.Diff repoDiff, GitRepository repo) : base(innerCommit)
     {
+        repoDiff.NotNull();
+        repo.NotNull();
         this.innerCommit = innerCommit.NotNull();
-        this.parentsLazy = new(() => innerCommit.Parents.Select(parent => new Commit(parent, repoDiff)).ToList());
+        this.parentsLazy = new(() => innerCommit.Parents.Select(parent => repo.GetOrCreate(parent, repoDiff)).ToList());
         When = innerCommit.Committer.When;
         this.repoDiff = repoDiff;
     }

src/GitVersion.LibGit2Sharp/Git/CommitCollection.cs

@@ -8,12 +8,14 @@ internal sealed class CommitCollection : ICommitCollection
     private readonly ICommitLog innerCollection;
     private readonly Lazy<IReadOnlyCollection<ICommit>> commits;
     private readonly Diff diff;
+    private readonly GitRepository repo;
 
-    internal CommitCollection(ICommitLog collection, Diff diff)
+    internal CommitCollection(ICommitLog collection, Diff diff, GitRepository repo)
     {
         this.innerCollection = collection.NotNull();
-        this.commits = new Lazy<IReadOnlyCollection<ICommit>>(() => [.. this.innerCollection.Select(commit => new Commit(commit, diff))]);
+        this.commits = new Lazy<IReadOnlyCollection<ICommit>>(() => [.. this.innerCollection.Select(commit => repo.GetOrCreate(commit, diff))]);
         this.diff = diff.NotNull();
+        this.repo = repo.NotNull();
     }
 
     public IEnumerator<ICommit> GetEnumerator()
@@ -36,7 +38,7 @@ public IEnumerable<ICommit> QueryBy(CommitFilter commitFilter)
             SortBy = (LibGit2Sharp.CommitSortStrategies)commitFilter.SortBy
         };
         var commitLog = ((IQueryableCommitLog)this.innerCollection).QueryBy(filter);
-        return new CommitCollection(commitLog, this.diff);
+        return new CommitCollection(commitLog, this.diff, this.repo);
 
         static object? GetReacheableFrom(object? item) =>
             item switch

src/GitVersion.LibGit2Sharp/Git/GitRepository.cs

@@ -1,3 +1,4 @@
+using System.Collections.Concurrent;
 using GitVersion.Extensions;
 using GitVersion.Helpers;
 using LibGit2Sharp;
@@ -8,6 +9,10 @@ internal sealed partial class GitRepository
 {
     private Lazy<IRepository>? repositoryLazy;
 
+    private readonly ConcurrentDictionary<string, Branch> cachedBranches = new();
+    private readonly ConcurrentDictionary<string, Commit> cachedCommits = new();
+    private readonly ConcurrentDictionary<string, Tag> cachedTags = new();
+
     private IRepository RepositoryInstance
     {
         get
@@ -20,12 +25,12 @@ private IRepository RepositoryInstance
     public string WorkingDirectory => RepositoryInstance.Info.WorkingDirectory;
     public bool IsHeadDetached => RepositoryInstance.Info.IsHeadDetached;
     public bool IsShallow => RepositoryInstance.Info.IsShallow;
-    public IBranch Head => new Branch(RepositoryInstance.Head, RepositoryInstance.Diff);
+    public IBranch Head => GetOrCreate(RepositoryInstance.Head, RepositoryInstance.Diff);
 
-    public ITagCollection Tags => new TagCollection(RepositoryInstance.Tags, RepositoryInstance.Diff);
+    public ITagCollection Tags => new TagCollection(RepositoryInstance.Tags, RepositoryInstance.Diff, this);
     public IReferenceCollection Refs => new ReferenceCollection(RepositoryInstance.Refs);
-    public IBranchCollection Branches => new BranchCollection(RepositoryInstance.Branches, RepositoryInstance.Diff);
-    public ICommitCollection Commits => new CommitCollection(RepositoryInstance.Commits, RepositoryInstance.Diff);
+    public IBranchCollection Branches => new BranchCollection(RepositoryInstance.Branches, RepositoryInstance.Diff, this);
+    public ICommitCollection Commits => new CommitCollection(RepositoryInstance.Commits, RepositoryInstance.Diff, this);
     public IRemoteCollection Remotes => new RemoteCollection(RepositoryInstance.Network.Remotes);
 
     public void DiscoverRepository(string? gitDirectory)
@@ -48,7 +53,7 @@ public void DiscoverRepository(string? gitDirectory)
             var first = (Commit)commit;
             var second = (Commit)otherCommit;
             var mergeBase = RepositoryInstance.ObjectDatabase.FindMergeBase(first, second);
-            return mergeBase == null ? null : new Commit(mergeBase, RepositoryInstance.Diff);
+            return mergeBase == null ? null : GetOrCreate(mergeBase, RepositoryInstance.Diff);
         });
     }
 
@@ -58,6 +63,26 @@ public int UncommittedChangesCount()
         return retryAction.Execute(GetUncommittedChangesCountInternal);
     }
 
+    public Branch GetOrCreate(LibGit2Sharp.Branch innerBranch, Diff repoDiff)
+    {
+        if (innerBranch.Tip is null)
+        {
+            return new Branch(innerBranch, repoDiff, this);
+        }
+
+        var cacheKey = $"{innerBranch.CanonicalName}|{innerBranch.Tip.Sha}|{innerBranch.RemoteName}";
+        return cachedBranches.GetOrAdd(cacheKey, new Branch(innerBranch, repoDiff, this));
+    }
+
+    public Commit GetOrCreate(LibGit2Sharp.Commit innerCommit, Diff repoDiff) =>
+        cachedCommits.GetOrAdd(innerCommit.Sha, new Commit(innerCommit, repoDiff, this));
+
+    public Tag GetOrCreate(LibGit2Sharp.Tag innerTag, Diff repoDiff)
+    {
+        var cacheKey = $"{innerTag.CanonicalName}|{innerTag.Target.Sha}";
+        return cachedTags.GetOrAdd(cacheKey, new Tag(innerTag, repoDiff, this));
+    }
+
     public void Dispose()
     {
         if (this.repositoryLazy is { IsValueCreated: true }) RepositoryInstance.Dispose();

src/GitVersion.LibGit2Sharp/Git/Tag.cs

@@ -11,12 +11,14 @@ internal sealed class Tag : ITag
     private readonly LibGit2Sharp.Tag innerTag;
     private readonly Diff diff;
     private readonly Lazy<ICommit?> commitLazy;
+    private readonly GitRepository repo;
 
-    internal Tag(LibGit2Sharp.Tag tag, Diff diff)
+    internal Tag(LibGit2Sharp.Tag tag, Diff diff, GitRepository repo)
     {
         this.innerTag = tag.NotNull();
         this.commitLazy = new(PeeledTargetCommit);
         this.diff = diff.NotNull();
+        this.repo = repo.NotNull();
         Name = new(this.innerTag.CanonicalName);
     }
 
@@ -35,7 +37,7 @@ internal Tag(LibGit2Sharp.Tag tag, Diff diff)
             target = annotation.Target;
         }
 
-        return target is LibGit2Sharp.Commit commit ? new Commit(commit, this.diff) : null;
+        return target is LibGit2Sharp.Commit commit ? this.repo.GetOrCreate(commit, this.diff) : null;
     }
 
     public override bool Equals(object? obj) => Equals(obj as ITag);

src/GitVersion.LibGit2Sharp/Git/TagCollection.cs

@@ -6,10 +6,12 @@ internal sealed class TagCollection : ITagCollection
 {
     private readonly Lazy<IReadOnlyCollection<ITag>> tags;
 
-    internal TagCollection(LibGit2Sharp.TagCollection collection, LibGit2Sharp.Diff diff)
+    internal TagCollection(LibGit2Sharp.TagCollection collection, LibGit2Sharp.Diff diff, GitRepository repo)
     {
-        collection = collection.NotNull();
-        this.tags = new Lazy<IReadOnlyCollection<ITag>>(() => [.. collection.Select(tag => new Tag(tag, diff))]);
+        collection.NotNull();
+        diff.NotNull();
+        repo.NotNull();
+        this.tags = new Lazy<IReadOnlyCollection<ITag>>(() => [.. collection.Select(tag => repo.GetOrCreate(tag, diff))]);
     }
 
     public IEnumerator<ITag> GetEnumerator()