[hpetriffer]

Summary

Closing a large solution blocked the UI thread for minutes. Classic projects stayed at "0 of x projects" in the close dialog; SDK projects hung after "Closed solution".

XSolution.Close() closed each project, and every close removed that project from the references of all other projects. Each removed reference saved the reference list through the AssemblyReferences property, which runs ResolveReferences() and re-reads assemblies from disk. The database was already closed at that point, so all of this work was thrown away.

 XSolution.Close()
   XDatabase.CloseDatabase()
+  _projects.Clear()                       // list emptied first
   foreach project
-    project.UnLoad()
     project.Close()
       XSolution.Remove(project)
-        foreach otherProject
-          otherProject.RemoveProjectReference()
-            RemoveAssemblyReference()
-              SaveAssemblyReferencesToDatabase()
-                AssemblyReferences  -> ResolveReferences() -> XAssembly.Read()
+        returns at once (_projects is empty)
       UnLoad()

SaveAssemblyReferencesToDatabase() now passes the _AssemblyReferences field, so saving never triggers reference resolution.

Unloading or removing a single project still goes through XSolution.Remove() with the full reference cleanup.

Evidence

Intellisense log, time the code model needs on solution close:

• Before (installed builds): RadixWfSDK.slnx (SDK, 110 projects, X# 3.1.0.0 in VS 18, closed ~2 minutes after opening): XSolution.Close() ran for more than 3 minutes after "Closed solution", with 26,000+ "Database is not open" calls on the UI thread. RadixWf.sln (98 classic projects, X# 3.0.x): 1–10 s normally, 13 and 17 minutes in two sessions.
  After (this branch, VS 2022 experimental instance, both solutions closed 1–2 minutes after loading): RadixWfSDK.slnx 3.8 s, RadixWf.sln 2.1 s. In both, nearly all of that time is SaveToDisk + VACUUM of the database; no XSolution.Remove() calls and no database access after the database was closed.

Merge Danger

Door: two-way

Blast Radius: solution-close

Only the code path for closing the whole solution changes. Not addressed here: CPS background threads still resolve references while the database is being closed, which logs InvalidOperationException and NullReferenceException in AssemblyReader.AddType. That race existed before this change and does not block the UI thread.

🤖 Generated with Claude Code

[RobertvanderHulst]

Great catch. This really makes a difference!