ORMap and friends have deltas (#22350)

akka-distributed-data/src/test/scala/akka/cluster/ddata/ORMultiMapSpec.scala

@@ -77,6 +77,12 @@ class ORMultiMapSpec extends WordSpec with Matchers {
 
       val merged2 = m2 merge m1
       merged2.entries should be(expectedMerged)
+
+      val merged3 = m1 mergeDelta m2.delta.get
+      merged3.entries should be(expectedMerged)
+
+      val merged4 = m2 mergeDelta m1.delta.get
+      merged4.entries should be(expectedMerged)
     }
   }
 
@@ -107,6 +113,74 @@ class ORMultiMapSpec extends WordSpec with Matchers {
     m2.entries should be(Map("b" → Set("B1")))
   }
 
+  "not have usual anomalies for remove+addBinding scenario and delta-deltas" in {
+    val m1 = ORMultiMap.emptyWithValueDeltas[String, String].put(node1, "a", Set("A")).put(node1, "b", Set("B"))
+    val m2 = ORMultiMap.emptyWithValueDeltas[String, String].put(node2, "c", Set("C"))
+
+    val merged1 = m1 merge m2
+
+    val m3 = merged1.resetDelta.remove(node1, "b")
+    val m4 = merged1.resetDelta.addBinding(node1, "b", "B2")
+
+    val merged2 = m3 merge m4
+
+    merged2.entries("a") should be(Set("A"))
+    merged2.entries("b") should be(Set("B2"))
+    merged2.entries("c") should be(Set("C"))
+
+    val merged3 = m3 mergeDelta m4.delta.get
+
+    merged3.entries("a") should be(Set("A"))
+    merged3.entries("b") should be(Set("B2"))
+    merged3.entries("c") should be(Set("C"))
+  }
+
+  "not have usual anomalies for remove+addBinding scenario and delta-deltas 2" in {
+    // the new delta-delta ORMultiMap is free from this anomaly
+    val m1 = ORMultiMap.emptyWithValueDeltas[String, String].put(node1, "a", Set("A")).put(node1, "b", Set("B"))
+    val m2 = ORMultiMap.emptyWithValueDeltas[String, String].put(node2, "c", Set("C"))
+
+    // m1 - node1 gets the update from m2
+    val merged1 = m1 merge m2
+    // m2 - node2 gets the update from m1
+    val merged2 = m2 merge m1
+
+    // no race condition
+    val m3 = merged1.resetDelta.remove(node1, "b")
+    // let's imagine that m3 (node1) update gets propagated here (full state or delta - doesn't matter)
+    // and is in flight, but in the meantime, an element is being added somewhere else (m4 - node2)
+    // and the update is propagated before the update from node1 is merged
+    val m4 = merged2.resetDelta.addBinding(node2, "b", "B2")
+    // and later merged on node1
+    val merged3 = m3 merge m4
+    // and the other way round...
+    val merged4 = m4 merge m3
+
+    // result -  the element "B" is kept on both sides...
+    merged3.entries("a") should be(Set("A"))
+    merged3.entries("b") should be(Set("B2"))
+    merged3.entries("c") should be(Set("C"))
+
+    merged4.entries("a") should be(Set("A"))
+    merged4.entries("b") should be(Set("B2"))
+    merged4.entries("c") should be(Set("C"))
+
+    // but if the timing was slightly different, so that the update from node1
+    // would get merged just before update on node2:
+    val merged5 = (m2 merge m3).resetDelta.addBinding(node2, "b", "B2")
+    // the update propagated ... and merged on node1:
+    val merged6 = m3 merge merged5
+
+    // then the outcome would be the same...
+    merged5.entries("a") should be(Set("A"))
+    merged5.entries("b") should be(Set("B2"))
+    merged5.entries("c") should be(Set("C"))
+
+    merged6.entries("a") should be(Set("A"))
+    merged6.entries("b") should be(Set("B2"))
+    merged6.entries("c") should be(Set("C"))
+  }
+
   "have unapply extractor" in {
     val m1 = ORMultiMap.empty.put(node1, "a", Set(1L, 2L)).put(node2, "b", Set(3L))
     val m2: ORMultiMap[String, Long] = m1