client API: be more explicit about what can be done in wakeup callbacks

Don't leave any room for interpretation.

libmpv/client.h

@@ -1588,11 +1588,19 @@ void mpv_wakeup(mpv_handle *ctx);
  *
  * Keep in mind that the callback will be called from foreign threads. You
  * must not make any assumptions of the environment, and you must return as
- * soon as possible. You are not allowed to call any client API functions
- * inside of the callback. In particular, you should not do any processing in
- * the callback, but wake up another thread that does all the work. It's also
- * possible that the callback is called from a thread while a mpv API function
- * is called (i.e. it can be reentrant).
+ * soon as possible (i.e. no long blocking waits). Exiting the callback through
+ * any other means than a normal return is forbidden (no throwing exceptions,
+ * no longjmp() calls). You must not change any local thread state (such as
+ * the C floating point environment).
+ *
+ * You are not allowed to call any client API functions inside of the callback.
+ * In particular, you should not do any processing in the callback, but wake up
+ * another thread that does all the work. The callback is meant strictly for
+ * notification only, and is called from arbitrary core parts of the player,
+ * that make no considerations for reentrant API use or allowing the callee to
+ * spend a lot of time doing other things. Keep in mind that it's also possible
+ * that the callback is called from a thread while a mpv API function is called
+ * (i.e. it can be reentrant).
  *
  * In general, the client API expects you to call mpv_wait_event() to receive
  * notifications, and the wakeup callback is merely a helper utility to make

libmpv/opengl_cb.h

@@ -252,7 +252,8 @@ typedef void *(*mpv_opengl_cb_get_proc_address_fn)(void *fn_ctx, const char *nam
  * Set the callback that notifies you when a new video frame is available, or
  * if the video display configuration somehow changed and requires a redraw.
  * Similar to mpv_set_wakeup_callback(), you must not call any mpv API from
- * the callback.
+ * the callback, and all the other listed restrictions apply (such as not
+ * exiting the callback by throwing exceptions).
  *
  * @param callback callback(callback_ctx) is called if the frame should be
  *                 redrawn