From 02f23141395d5407302cc695374079320ac4c92e Mon Sep 17 00:00:00 2001
From: Alex Mendoza <05alex.mendozaa@gmail.com>
Date: Sat, 27 Jun 2026 16:36:29 +0200
Subject: [PATCH] [SHELL32] Implement LockServer (#9055)

---
 dll/win32/shell32/shell32.cpp                 | 30 ++++++++-
 .../rostests/apitests/shell32/CMakeLists.txt  |  1 +
 .../rostests/apitests/shell32/LockServer.cpp  | 66 +++++++++++++++++++
 modules/rostests/apitests/shell32/testlist.c  |  2 +
 4 files changed, 97 insertions(+), 2 deletions(-)
 create mode 100644 modules/rostests/apitests/shell32/LockServer.cpp

diff --git a/dll/win32/shell32/shell32.cpp b/dll/win32/shell32/shell32.cpp
index 0ae868780d1..ab3209d8481 100644
--- a/dll/win32/shell32/shell32.cpp
+++ b/dll/win32/shell32/shell32.cpp
@@ -209,8 +209,34 @@ HRESULT WINAPI IDefClFImpl::CreateInstance(IUnknown * pUnkOuter, REFIID riid, LP
  */
 HRESULT WINAPI IDefClFImpl::LockServer(BOOL fLock)
 {
-    TRACE("%p->(0x%x), not implemented\n", this, fLock);
-    return E_NOTIMPL;
+    TRACE("%p->(0x%x)\n", this, fLock);
+
+    if (fLock)
+    {
+        if (pcRefDll)
+        {
+            if (*pcRefDll == LONG_MAX)
+                ERR("pcRefDll is pinned, not incrementing\n");
+            else
+                InterlockedIncrement(pcRefDll);
+        }
+        _pAtlModule->Lock();
+    }
+    else
+    {
+        _pAtlModule->Unlock();
+        if (pcRefDll)
+        {
+            if (*pcRefDll == LONG_MAX)
+                ERR("pcRefDll is pinned, not decrementing\n");
+            else if (*pcRefDll > 0)
+                InterlockedDecrement(pcRefDll);
+            else
+                ERR("pcRefDll underflow\n");
+        }
+    }
+
+    return S_OK;
 }
 
 /**************************************************************************
diff --git a/modules/rostests/apitests/shell32/CMakeLists.txt b/modules/rostests/apitests/shell32/CMakeLists.txt
index 596374dafa8..e2f793d26c2 100644
--- a/modules/rostests/apitests/shell32/CMakeLists.txt
+++ b/modules/rostests/apitests/shell32/CMakeLists.txt
@@ -17,6 +17,7 @@ list(APPEND SOURCE
     FindExecutable.cpp
     GetDisplayNameOf.cpp
     GUIDFromString.cpp
+    LockServer.cpp
     Int64ToString.cpp
     IShellFolderViewCB.cpp
     ItemIDList.cpp
diff --git a/modules/rostests/apitests/shell32/LockServer.cpp b/modules/rostests/apitests/shell32/LockServer.cpp
new file mode 100644
index 00000000000..a049117cadb
--- /dev/null
+++ b/modules/rostests/apitests/shell32/LockServer.cpp
@@ -0,0 +1,66 @@
+/*
+ * PROJECT:     ReactOS API tests
+ * LICENSE:     MIT (https://spdx.org/licenses/MIT)
+ * PURPOSE:     Test for LockServer
+ * COPYRIGHT:   Copyright 2026 Alex Mendoza <05alex.mendozaa@gmail.com>
+ */
+
+#include "shelltest.h"
+#include <undocshell.h>
+
+static HRESULT CALLBACK CreateInstanceStub(IUnknown *pUnkOuter, REFIID riid, LPVOID *ppv)
+{
+    *ppv = NULL;
+    return E_NOTIMPL;
+}
+
+static void test_LockServer(void)
+{
+    IClassFactory *pcf = NULL;
+    LONG refDll = 0;
+    HRESULT hr;
+
+    hr = SHCreateDefClassObject(IID_IClassFactory,
+                                (LPVOID*)&pcf,
+                                CreateInstanceStub,
+                                (LPDWORD)&refDll,
+                                IID_IUnknown);
+    ok(hr == S_OK, "SHCreateDefClassObject failed: %08lx\n", hr);
+    ok(pcf != NULL, "pcf is NULL\n");
+    if (!pcf)
+    {
+        skip("pcf is NULL, skipping LockServer tests\n");
+        return;
+    }
+
+    ok(refDll == 1, "Expected refDll == 1 after init, got %ld\n", refDll);
+
+    hr = pcf->LockServer(TRUE);
+    ok(hr == S_OK, "LockServer() failed: %08lx\n", hr);
+    ok(refDll == 2, "Expected refDll == 2 after lock, got %ld\n", refDll);
+
+    hr = pcf->LockServer(FALSE);
+    ok(hr == S_OK, "LockServer() failed: %08lx\n", hr);
+    ok(refDll == 1, "Expected refDll == 1 after unlock, got %ld\n", refDll);
+
+    hr = pcf->LockServer(FALSE);
+    ok(hr == S_OK, "LockServer() failed: %08lx\n", hr);
+    ok(refDll >= 0, "refDll went negative after unlock when not locked: %ld\n", refDll);
+
+    hr = pcf->LockServer(TRUE);
+    ok(hr == S_OK, "LockServer() failed: %08lx\n", hr);
+    hr = pcf->LockServer(TRUE);
+    ok(hr == S_OK, "LockServer() failed: %08lx\n", hr);
+    hr = pcf->LockServer(FALSE);
+    ok(hr == S_OK, "LockServer() failed: %08lx\n", hr);
+    hr = pcf->LockServer(FALSE);
+    ok(hr == S_OK, "LockServer() failed: %08lx\n", hr);
+
+    pcf->Release();
+    ok(refDll == 0, "Expected refDll == 0 after Release, got %ld\n", refDll);
+}
+
+START_TEST(LockServer)
+{
+    test_LockServer();
+}
diff --git a/modules/rostests/apitests/shell32/testlist.c b/modules/rostests/apitests/shell32/testlist.c
index 479dd474ca3..9bf2c1cf66d 100644
--- a/modules/rostests/apitests/shell32/testlist.c
+++ b/modules/rostests/apitests/shell32/testlist.c
@@ -21,6 +21,7 @@ extern void func_ILCreateFromPath(void);
 extern void func_ILIsEqual(void);
 extern void func_Int64ToString(void);
 extern void func_IShellFolderViewCB(void);
+extern void func_LockServer(void);
 extern void func_menu(void);
 extern void func_OpenAs_RunDLL(void);
 extern void func_PathIsEqualOrSubFolder(void);
@@ -80,6 +81,7 @@ const struct test winetest_testlist[] =
     { "ILIsEqual", func_ILIsEqual },
     { "Int64ToString", func_Int64ToString },
     { "IShellFolderViewCB", func_IShellFolderViewCB },
+    { "LockServer", func_LockServer },
     { "menu", func_menu },
     //{ "OpenAs_RunDLL", func_OpenAs_RunDLL }, // Test hangs on Win 2003
     { "PathIsEqualOrSubFolder", func_PathIsEqualOrSubFolder },