Implement QLibrary::PreventUnloadHint for Windows

It's interesting that the HMODULE/HINSTANCE pointer points to something
in the actual module that got loaded, so we can use its value as
"address of something in the module" for GetModuleHandleEx. The "PIN"
flag tells the Windows DLL loader to never unload.

Change-Id: Ifea6e497f11a461db432ffff1449a2169eb6293e
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Kai Koehne <kai.koehne@qt.io>
Reviewed-by: Joerg Bornemann <joerg.bornemann@theqtcompany.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/src/corelib/plugin/qlibrary_win.cpp b/src/corelib/plugin/qlibrary_win.cpp
index deec54db0a..95e5afa837 100644
--- a/src/corelib/plugin/qlibrary_win.cpp
+++ b/src/corelib/plugin/qlibrary_win.cpp
@@ -148,6 +148,16 @@ bool QLibraryPrivate::load_sys()
         else
             qualifiedFileName = dir.filePath(moduleFileName);
 #endif // !Q_OS_WINRT
+
+        if (loadHints() & QLibrary::PreventUnloadHint) {
+            // prevent the unloading of this component
+            HMODULE hmod;
+            bool ok = GetModuleHandleEx(GET_MODULE_HANDLE_EX_FLAG_PIN |
+                                        GET_MODULE_HANDLE_EX_FLAG_FROM_ADDRESS,
+                                        reinterpret_cast<const wchar_t *>(pHnd),
+                                        &hmod);
+            Q_ASSERT(!ok || hmod == pHnd);
+        }
     }
     return (pHnd != 0);
 }