Add detection of OSX NSApp event loop.

lib/matplotlib/backends/__init__.py

@@ -25,7 +25,8 @@ def _get_current_event_loop():
     Returns
     -------
     Optional[str]
-        A value in {"qt5", "qt4", "gtk3", "gtk2", "tk", "headless", None}
+        One of the following values: "qt5", "qt4", "gtk3", "gtk2", "tk",
+        "macosx", "headless", ``None``.
     """
     QtWidgets = (sys.modules.get("PyQt5.QtWidgets")
                  or sys.modules.get("PySide2.QtWidgets"))
@@ -48,6 +49,16 @@ def _get_current_event_loop():
                        and frame.f_code.co_name == "mainloop"
                        for frame in sys._current_frames().values()):
         return "tk"
+    try:
+        from matplotlib.backends import _macosx
+    except ImportError:
+        pass
+    else:
+        # Note that the NSApp event loop is also running when a non-native
+        # toolkit (e.g. Qt5) is active, but in that case we want to report the
+        # other toolkit; thus, this check comes after the other toolkits.
+        if _macosx.event_loop_is_running():
+            return "macosx"
     if sys.platform.startswith("linux") and not os.environ.get("DISPLAY"):
         return "headless"
 

src/_macosx.m

@@ -2818,6 +2818,16 @@ - (int)index
 }
 @end
 
+static PyObject*
+event_loop_is_running(PyObject* self)
+{
+    if ([NSApp isRunning]) {
+        Py_RETURN_TRUE;
+    } else {
+        Py_RETURN_FALSE;
+    }
+}
+
 static PyObject*
 show(PyObject* self)
 {
@@ -3072,10 +3082,17 @@ static bool verify_framework(void)
 }
 
 static struct PyMethodDef methods[] = {
+   {"event_loop_is_running",
+    (PyCFunction)event_loop_is_running,
+    METH_NOARGS,
+    "Return whether the NSApp main event loop is currently running."
+   },
    {"show",
     (PyCFunction)show,
     METH_NOARGS,
-    "Show all the figures and enter the main loop.\nThis function does not return until all Matplotlib windows are closed,\nand is normally not needed in interactive sessions."
+    "Show all the figures and enter the main loop.\n"
+    "This function does not return until all Matplotlib windows are closed,\n"
+    "and is normally not needed in interactive sessions."
    },
    {"choose_save_file",
     (PyCFunction)choose_save_file,
@@ -3087,7 +3104,7 @@ static bool verify_framework(void)
     METH_VARARGS,
     "Sets the active cursor."
    },
-   {NULL,          NULL, 0, NULL}/* sentinel */
+   {NULL, NULL, 0, NULL} /* sentinel */
 };
 
 #if PY3K