Add error message when terminating the MuJoCo renderer without callin…

…g `env.close` (#1283)

Co-authored-by: Ayesh Ahmad <[email protected]>

gymnasium/envs/mujoco/mujoco_rendering.py

@@ -7,6 +7,8 @@
 import mujoco
 import numpy as np
 
+from gymnasium.logger import warn
+
 
 def _import_egl(width, height):
     from mujoco.egl import GLContext
@@ -356,11 +358,22 @@ def make_context_current(self):
         glfw.make_context_current(self.window)
 
     def free(self):
-        if self.window:
-            if glfw.get_current_context() == self.window:
-                glfw.make_context_current(None)
-            glfw.destroy_window(self.window)
-            self.window = None
+        """
+        Safely frees the OpenGL context and destroys the GLFW window,
+        handling potential issues during interpreter shutdown or resource cleanup.
+        """
+        try:
+            if self.window:
+                if glfw.get_current_context() == self.window:
+                    glfw.make_context_current(None)
+                glfw.destroy_window(self.window)
+                self.window = None
+        except AttributeError:
+            # Handle cases where attributes are missing due to improper environment closure
+            warn(
+                "Environment was not properly closed using 'env.close()'. Please ensure to close the environment explicitly. "
+                "GLFW module or dependencies are unloaded. Window cleanup might not have completed."
+            )
 
     def __del__(self):
         """Eliminate all of the OpenGL glfw contexts and windows"""