qoperatingsystemversion_win: fix thread race

If two threads call the function at the same time before the static is initialized
one of them may end up with a half-written object.

Amends 3fe89eec61e2c819bb54a5d3dfe4bc29dba49ff3

Pick-to: 6.2
Change-Id: Ie08970f9ee283fd75292a8b44a1fca89de4b04eb
Reviewed-by: Yuhang Zhao <2546789017@qq.com>
Reviewed-by: Marc Mutz <marc.mutz@qt.io>

1 files changed, 4 insertions, 3 deletions

diff --git a/src/corelib/global/qoperatingsystemversion_win.cpp b/src/corelib/global/qoperatingsystemversion_win.cpp
index e8c32be56b..c052cd9c9e 100644
--- a/src/corelib/global/qoperatingsystemversion_win.cpp
+++ b/src/corelib/global/qoperatingsystemversion_win.cpp
@@ -110,14 +110,15 @@ OSVERSIONINFOEX qWindowsVersionInfo()
 
 QOperatingSystemVersion QOperatingSystemVersion::current()
 {
-    static QOperatingSystemVersion v;
-    if (v.m_os == Unknown) {
+    static QOperatingSystemVersion v = [](){
+        QOperatingSystemVersion v;
         v.m_os = currentType();
         const OSVERSIONINFOEX osv = qWindowsVersionInfo();
         v.m_major = osv.dwMajorVersion;
         v.m_minor = osv.dwMinorVersion;
         v.m_micro = osv.dwBuildNumber;
-    }
+        return v;
+    }();
     return v;
 }