+ * is called.
+ *
+ * Note that this is called both by the event loop, when a I/O thread
+ * sends a byte in the notification pipe, and is also directly called from
+ * waitEmptyIOJobsQueue().
+ *
+ * In the latter case we don't want to swap more, so we use the
+ * "privdata" argument setting it to a not NULL value to signal this
+ * condition. */