[2207] Documentation update

src/lib/datasrc/memory/zone_table_segment.h

@@ -138,7 +138,8 @@ public:
     /// \param origin The origin of the zone to reload.
     /// \param rrclass The class of the zone to reload.
     /// \return New instance of a zone writer. The ownership is passed
-    ///     onto the caller.
+    ///     onto the caller and the caller needs to \c delete it when
+    ///     it's done with the writer.
     virtual ZoneWriter* getZoneWriter(const LoadAction& load_action,
                                       const dns::Name& origin,
                                       const dns::RRClass& rrclass) = 0;

src/lib/datasrc/memory/zone_writer.h

@@ -30,6 +30,11 @@ namespace memory {
 /// We divide them so the update of zone data can be done asynchronously,
 /// in a different thread. The install() operation is the only one that needs
 /// to be done in a critical section.
+///
+/// Each derived class implementation must provide the strong exception
+/// guarantee for each public method. That is, when any of the methods
+/// throws, the entire state should stay the same as before the call
+/// (how to achieve that may be implementation dependant).
 class ZoneWriter {
 public:
     /// \brief Get the zone data into memory.