Windows: Fix QLockFile hanging when file cannot be created.

Return QLockFile::PermissionError when file does not exist, preventing
the stale file detection logic from triggering.

Add Windows-only autotest trying to create a lock file in
a system folder guarded with checks for elevated processes
and UAC virtualization.

Task-number: QTBUG-45631
Change-Id: I1790f8f925660f6bf1df94c2ced901e6ec57cbb0
Reviewed-by: Joerg Bornemann <joerg.bornemann@theqtcompany.com>
Reviewed-by: Oliver Wolff <oliver.wolff@theqtcompany.com>

1 files changed, 12 insertions, 1 deletions

diff --git a/src/corelib/io/qlockfile_win.cpp b/src/corelib/io/qlockfile_win.cpp
index a36e6e93b8..9fe86e1ad8 100644
--- a/src/corelib/io/qlockfile_win.cpp
+++ b/src/corelib/io/qlockfile_win.cpp
@@ -48,6 +48,12 @@ static inline QByteArray localHostName()
     return qgetenv("COMPUTERNAME");
 }
 
+static inline bool fileExists(const wchar_t *fileName)
+{
+    WIN32_FILE_ATTRIBUTE_DATA  data;
+    return GetFileAttributesEx(fileName, GetFileExInfoStandard, &data);
+}
+
 QLockFile::LockError QLockFilePrivate::tryLock_sys()
 {
     const QFileSystemEntry fileEntry(fileName);
@@ -79,8 +85,13 @@ QLockFile::LockError QLockFilePrivate::tryLock_sys()
         case ERROR_SHARING_VIOLATION:
         case ERROR_ALREADY_EXISTS:
         case ERROR_FILE_EXISTS:
-        case ERROR_ACCESS_DENIED: // readonly file, or file still in use by another process. Assume the latter, since we don't create it readonly.
             return QLockFile::LockFailedError;
+        case ERROR_ACCESS_DENIED:
+            // readonly file, or file still in use by another process.
+            // Assume the latter if the file exists, since we don't create it readonly.
+            return fileExists((const wchar_t*)fileEntry.nativeFilePath().utf16())
+                ? QLockFile::LockFailedError
+                : QLockFile::PermissionError;
         default:
             qWarning() << "Got unexpected locking error" << lastError;
             return QLockFile::UnknownError;