+
+ /* If called from a different thread, we first check to see if
+ * the calling thread is registered with this UI. If so, there
+ * is a per-thread ringbuffer of requests that ::get_request()
+ * just set up a new request in. If so, all we need do here is
+ * to advance the write ptr in that ringbuffer so that the next
+ * request by this calling thread will use the next slot in
+ * the ringbuffer. The ringbuffer has
+ * single-reader/single-writer semantics because the calling
+ * thread is the only writer, and the UI event loop is the only
+ * reader.
+ */
+