+ /* This will be read/written by multiple threads without a lock -- you
+ * should take a snapshot and use it to see if you happen to be in the
+ * CL's handles at this position, to make most lookups O(1). It's
+ * volatile to make sure that the compiler doesn't emit multiple loads
+ * from the address, which would make the lookup racy.
+ */
+ volatile uint32_t last_hindex;
+