- * A) "read" after "write" will always return the result of the latest
- * write.
- * B) "write" after "read" will never be returned by the read.
- * C) It is guaranteed that after a grace period following a "del" and
- * "replace" operation, no reference to the removed items exists in
- * the hash table.
- * D) Uniqueness guarantee: when using add_unique and/or add_replace to
- * insert nodes into the table, if there was previously one node or
- * less with the same key being inserted by one or more concurrent
- * add_unique and/or add_replace, all concurrent "read" performed on
- * the hash table are guaranteed to find one, and only one node with
- * that key.
+ * A.1) "read" after "write": if there is ordering between a write and a
+ * later read, then the read is guaranteed to see the write or some
+ * later write.
+ * A.2) "read traversal" after "write": given that there is dependency
+ * ordering between reads in a "read traversal", if there is
+ * ordering between a write and the first read of the traversal,
+ * then the "read traversal" is guaranteed to see the write or
+ * some later write.
+ * B.1) "write" after "read": if there is ordering between a read and a
+ * later write, then the read will never see the write.
+ * B.2) "write" after "read traversal": given that there is dependency
+ * ordering between reads in a "read traversal", if there is
+ * ordering between the last read of the traversal and a later
+ * write, then the "read traversal" will never see the write.
+ * C) "write" while "read traversal": if a write occurs during a "read
+ * traversal", the traversal may, or may not, see the write.
+ * D.1) "write" after "write": if there is ordering between a write and
+ * a later write, then the later write is guaranteed to see the
+ * effects of the first write.
+ * D.2) Concurrent "write" pairs: The system will assign an arbitrary
+ * order to any pair of concurrent conflicting writes.
+ * Non-conflicting writes (for example, to different keys) are
+ * unordered.
+ * E) If a grace period separates a "del" or "replace" operation
+ * and a subsequent operation, then that subsequent operation is
+ * guaranteed not to see the removed item.
+ * F) Uniqueness guarantee: given a hash table that does not contain
+ * duplicate items for a given key, there will only be one item in
+ * the hash table after an arbitrary sequence of add_unique and/or
+ * add_replace operations. Note, however, that a pair of
+ * concurrent read operations might well access two different items
+ * with that key.
+ * G.1) If a pair of lookups for a given key are ordered (e.g. by a
+ * memory barrier), then the second lookup will return the same
+ * node as the previous lookup, or some later node.
+ * G.2) A "read traversal" that starts after the end of a prior "read
+ * traversal" (ordered by memory barriers) is guaranteed to see the
+ * same nodes as the previous traversal, or some later nodes.
+ * G.3) Concurrent "read" pairs: concurrent reads are unordered. For
+ * example, if a pair of reads to the same key run concurrently
+ * with an insertion of that same key, the reads remain unordered
+ * regardless of their return values. In other words, you cannot
+ * rely on the values returned by the reads to deduce ordering.
+ *
+ * Progress guarantees:
+ *
+ * * Reads are wait-free. These operations always move forward in the
+ * hash table linked list, and this list has no loop.
+ * * Writes are lock-free. Any retry loop performed by a write operation
+ * is triggered by progress made within another update operation.