+cdd #16799 Add ORMultiMap data type

akka-docs/rst/scala/code/docs/ddata/DistributedDataDocSpec.scala

@@ -325,6 +325,19 @@ class DistributedDataDocSpec extends AkkaSpec(DistributedDataDocSpec.config) {
     //#orset
   }
 
+  "demonstrate ORMultiMap" in {
+    def println(o: Any): Unit = ()
+    //#ormultimap
+    implicit val node = Cluster(system)
+    val m0 = ORMultiMap.empty[Int]
+    val m1 = m0 + ("a" -> Set(1, 2, 3))
+    val m2 = m1.addBinding("a", 4)
+    val m3 = m2.removeBinding("a", 2)
+    val m4 = m3.addBinding("b", 1)
+    println(m4.entries)
+    //#ormultimap
+  }
+
   "demonstrate Flag" in {
     def println(o: Any): Unit = ()
     //#flag

akka-docs/rst/scala/distributed-data.rst

@@ -240,7 +240,7 @@ by this package, such as:
 
 * Counters: ``GCounter``, ``PNCounter``
 * Sets: ``GSet``, ``ORSet``
-* Maps: ``ORMap``, ``LWWMap``, ``PNCounterMap``
+* Maps: ``ORMap``, ``ORMultiMap``, ``LWWMap``, ``PNCounterMap``
 * Registers: ``LWWRegister``, ``Flag``
 
 Counters
@@ -303,12 +303,17 @@ It is rather inconvenient to use the ``ORMap`` directly since it does not expose
 of the values. The ``ORMap`` is intended as a low level tool for building more specific maps,
 such as the following specialized maps.
 
+``ORMultiMap`` (observed-remove multi-map) is a multi-map implementation that wraps an
+``ORMap`` with an ``ORSet`` for the map's value.
+
 ``PNCounterMap`` (positive negative counter map) is a map of named counters. It is a specialized 
 ``ORMap`` with ``PNCounter`` values.
 
 ``LWWMap`` (last writer wins map) is a specialized ``ORMap`` with ``LWWRegister`` (last writer wins register)
 values. 
 
+.. includecode:: code/docs/ddata/DistributedDataDocSpec.scala#ormultimap
+
 Note that ``LWWRegister`` and therefore ``LWWMap`` relies on synchronized clocks and should only be used
 when the choice of value is not important for concurrent updates occurring within the clock skew.