+/**
+ * glk_tick:
+ *
+ * Many platforms have some annoying thing that has to be done every so often,
+ * or the gnurrs come from the voodvork out and eat your computer.
+ *
+ * Well, not really. But you should call glk_tick() every so often, just in
+ * case. It may be necessary to yield time to other applications in a
+ * cooperative-multitasking OS, or to check for player interrupts in an infinite
+ * loop.
+ *
+ * This call is fast; in fact, on average, it does nothing at all. So you can
+ * call it often. (In a virtual machine interpreter, once per opcode is
+ * appropriate. In a program with lots of computation, pick a comparable rate.)
+ *
+ * glk_tick() does not try to update the screen, or check for player input, or
+ * any other interface task. For that, you should call glk_select() or
+ * glk_select_poll().
+ *
+ * Basically, you must ensure there's some fixed upper bound on the amount of
+ * computation that can occur before a glk_tick() (or glk_select()) occurs. In a
+ * VM interpreter, where the VM code might contain an infinite loop, this is
+ * critical. In a C program, you can often eyeball it.
+ */