Fix cmSystemTools::RenameFile race on Windows

Since commit d46d8df0 (Re-implemented cmGeneratedFileStream to look like a
real stream and replace the destination file atomically, 2004-11-03) our
RenameFile implementation tries to deal with MoveFile not replacing
read-only files.  In order to avoid the Get/SetFileAttributes pair we used
stat to test for existence of the destination file.  This has a race in
which the destination could be created between the test for existence and
the MoveFile call.

Remove the stat call and use GetFileAttributes to detect whether the file
exists.  This shortens the race but does not eliminate it.  Use a loop to
try multiple times in case we lose the race.  While at it, drop Win9x
support and always use MoveFileEx.

1 files changed, 20 insertions, 31 deletions

diff --git a/Source/cmSystemTools.cxx b/Source/cmSystemTools.cxx
index c2521d99fa..525efb4a56 100644
--- a/Source/cmSystemTools.cxx
+++ b/Source/cmSystemTools.cxx
@@ -1180,46 +1180,35 @@ bool cmSystemTools::CopyFileIfDifferent(const char* source,
 bool cmSystemTools::RenameFile(const char* oldname, const char* newname)
 {
 #ifdef _WIN32
-  /* On Windows the move functions will not replace existing files.
-     Check if the destination exists.  */
-  struct stat newFile;
-  if(stat(newname, &newFile) == 0)
+# ifndef INVALID_FILE_ATTRIBUTES
+#  define INVALID_FILE_ATTRIBUTES ((DWORD)-1)
+# endif
+  /* Windows MoveFileEx may not replace read-only or in-use files.  If it
+     fails then remove the read-only attribute from any existing destination.
+     Try multiple times since we may be racing against another process
+     creating/opening the destination file just before our MoveFileEx.  */
+  int tries = 5;
+  while(!MoveFileEx(oldname, newname, MOVEFILE_REPLACE_EXISTING) && --tries)
     {
-    /* The destination exists.  We have to replace it carefully.  The
-       MoveFileEx function does what we need but is not available on
-       Win9x.  */
-    OSVERSIONINFO osv;
-    DWORD attrs;
-
-    /* Make sure the destination is not read only.  */
-    attrs = GetFileAttributes(newname);
-    if(attrs & FILE_ATTRIBUTE_READONLY)
+    // Try again only if failure was due to access permissions.
+    if(GetLastError() != ERROR_ACCESS_DENIED)
       {
-      SetFileAttributes(newname, attrs & ~FILE_ATTRIBUTE_READONLY);
+      return false;
       }
-
-    /* Check the windows version number.  */
-    osv.dwOSVersionInfoSize = sizeof(osv);
-    GetVersionEx(&osv);
-    if(osv.dwPlatformId == VER_PLATFORM_WIN32_WINDOWS)
+    DWORD attrs = GetFileAttributes(newname);
+    if((attrs != INVALID_FILE_ATTRIBUTES) &&
+       (attrs & FILE_ATTRIBUTE_READONLY))
       {
-      /* This is Win9x.  There is no MoveFileEx implementation.  We
-         cannot quite rename the file atomically.  Just delete the
-         destination and then move the file.  */
-      DeleteFile(newname);
-      return MoveFile(oldname, newname) != 0;
+      // Remove the read-only attribute from the destination file.
+      SetFileAttributes(newname, attrs & ~FILE_ATTRIBUTE_READONLY);
       }
     else
       {
-      /* This is not Win9x.  Use the MoveFileEx implementation.  */
-      return MoveFileEx(oldname, newname, MOVEFILE_REPLACE_EXISTING) != 0;
+      // The file may be temporarily in use so wait a bit.
+      cmSystemTools::Delay(100);
       }
     }
-  else
-    {
-    /* The destination does not exist.  Just move the file.  */
-    return MoveFile(oldname, newname) != 0;
-    }
+  return tries > 0;
 #else
   /* On UNIX we have an OS-provided call to do this atomically.  */
   return rename(oldname, newname) == 0;