Fix stdout/stderr redirection temp files not being deleted when restarting calibre from within calibre on windows

src/calibre/gui2/main.py

@@ -323,6 +323,8 @@ def run_gui(opts, args, actions, listener, app, gui_debug=None):
                 app = os.path.dirname(os.path.dirname(sys.frameworks_dir))
                 subprocess.Popen('sleep 3s; open '+app, shell=True)
             else:
+                if iswindows and hasattr(winutil, 'prepare_for_restart'):
+                    winutil.prepare_for_restart()
                 subprocess.Popen([e] + sys.argv[1:])
     else:
         if iswindows:

src/calibre/utils/windows/winutil.c

@@ -815,6 +815,15 @@ winutil_internet_connected(PyObject *self, PyObject *args) {
     Py_RETURN_FALSE;
 }
 
+static PyObject *
+winutil_prepare_for_restart(PyObject *self, PyObject *args) {
+    FILE *f1 = NULL, *f2 = NULL;
+    if (stdout != NULL) fclose(stdout);
+    if (stderr != NULL) fclose(stderr);
+    _wfreopen_s(&f1, L"NUL", L"a+t", stdout);
+    _wfreopen_s(&f2, L"NUL", L"a+t", stderr);
+    Py_RETURN_NONE;
+}
 
 static PyObject *
 winutil_strftime(PyObject *self, PyObject *args)
@@ -978,6 +987,10 @@ be a unicode string. Returns unicode strings."
         "internet_connected()\n\nReturn True if there is an active internet connection"
     },
 
+    {"prepare_for_restart", winutil_prepare_for_restart, METH_VARARGS,
+        "prepare_for_restart()\n\nRedirect output streams so that the child process does not lock the temp files"
+    },
+
     {NULL, NULL, 0, NULL}
 };