Backport pull request #17884 from jellyfin/release-12.z

Release a folder's children once its subtree has been scanned

Original-merge: 2f2adae7d99537e53417f6d92aa3d40345a17b99

Merged-by: crobibero <cody@robibe.ro>

Backported-by: Cody Robibero <cody@robibe.ro>

1 files changed, 97 insertions, 0 deletions

diff --git a/tests/Jellyfin.Controller.Tests/Entities/FolderChildCacheTests.cs b/tests/Jellyfin.Controller.Tests/Entities/FolderChildCacheTests.cs
new file mode 100644
index 0000000000..705238317a
--- /dev/null
+++ b/tests/Jellyfin.Controller.Tests/Entities/FolderChildCacheTests.cs
@@ -0,0 +1,97 @@
+using System.Collections.Generic;
+using MediaBrowser.Controller.Entities;
+using Xunit;
+
+namespace Jellyfin.Controller.Tests.Entities;
+
+/// <summary>
+/// Covers <see cref="Folder.ReleaseCachedChildren"/>, which a recursive scan calls as it unwinds so
+/// the folders it walked do not keep the whole item graph of the library alive behind it.
+/// </summary>
+public class FolderChildCacheTests
+{
+    [Fact]
+    public void ReleaseCachedChildren_MakesTheNextAccessReload()
+    {
+        var folder = new TrackingFolder();
+
+        Assert.Empty(folder.Children);
+        Assert.Equal(1, folder.LoadCount);
+
+        // Second access is served from the cache on the instance.
+        Assert.Empty(folder.Children);
+        Assert.Equal(1, folder.LoadCount);
+
+        folder.ReleaseCachedChildren();
+
+        Assert.Empty(folder.Children);
+        Assert.Equal(2, folder.LoadCount);
+    }
+
+    [Fact]
+    public void ReleaseCachedChildren_ReachesEveryLevelBelow()
+    {
+        var leaf = new TrackingFolder();
+        var middle = new TrackingFolder { Source = [leaf] };
+        var root = new TrackingFolder { Source = [middle] };
+
+        // Walk the whole tree, as a recursive scan does, so every level holds its children.
+        Assert.Single(root.Children);
+        Assert.Single(middle.Children);
+        Assert.Empty(leaf.Children);
+        Assert.Equal(1, root.LoadCount);
+        Assert.Equal(1, middle.LoadCount);
+        Assert.Equal(1, leaf.LoadCount);
+
+        root.ReleaseCachedChildren();
+
+        Assert.Single(root.Children);
+        Assert.Single(middle.Children);
+        Assert.Empty(leaf.Children);
+        Assert.Equal(2, root.LoadCount);
+        Assert.Equal(2, middle.LoadCount);
+        Assert.Equal(2, leaf.LoadCount);
+    }
+
+    [Fact]
+    public void ReleaseCachedChildren_LoadsNothingThatIsNotAlreadyHeld()
+    {
+        var leaf = new TrackingFolder();
+        var root = new TrackingFolder { Source = [leaf] };
+
+        root.ReleaseCachedChildren();
+
+        Assert.Equal(0, root.LoadCount);
+        Assert.Equal(0, leaf.LoadCount);
+    }
+
+    [Fact]
+    public void ReleaseCachedChildren_TerminatesOnACycle()
+    {
+        var first = new TrackingFolder();
+        var second = new TrackingFolder { Source = [first] };
+        first.Source = [second];
+
+        Assert.Single(first.Children);
+        Assert.Single(second.Children);
+
+        // Clearing before descending is what stops this from recursing forever.
+        first.ReleaseCachedChildren();
+
+        Assert.Equal(1, first.LoadCount);
+        Assert.Equal(1, second.LoadCount);
+    }
+
+    private sealed class TrackingFolder : Folder
+    {
+        public int LoadCount { get; private set; }
+
+        public IReadOnlyList<BaseItem> Source { get; set; } = [];
+
+        protected override IReadOnlyList<BaseItem> LoadChildren()
+        {
+            LoadCount++;
+            return Source;
+        }
+    }
+}