use multiple channels in parallel [no ci]

eclair-core/src/main/scala/fr/acinq/eclair/router/Graph.scala

@@ -26,6 +26,7 @@ import fr.acinq.eclair.wire.protocol.ChannelUpdate
 import scala.annotation.tailrec
 import scala.collection.immutable.SortedMap
 import scala.collection.mutable
+import scala.util.Random
 
 object Graph {
 
@@ -229,7 +230,8 @@ object Graph {
           if (canRelayAmount && boundaries(neighborWeight) && !ignoredEdges.contains(edge.desc) && !ignoredVertices.contains(neighbor)) {
             val previousNeighborWeight = bestWeights.getOrElse(neighbor, RichWeight(MilliSatoshi(Long.MaxValue), Int.MaxValue, CltvExpiryDelta(Int.MaxValue), Double.MaxValue))
             // if this path between neighbor and the target has a shorter distance than previously known, we select it
-            if (neighborWeight.weight < previousNeighborWeight.weight) {
+            if (neighborWeight.weight < previousNeighborWeight.weight ||
+              (neighborWeight.weight == previousNeighborWeight.weight && Random.nextInt(1) == 0)) {
               // update the best edge for this vertex
               bestEdges.put(neighbor, edge)
               // add this updated node to the list for further exploration

eclair-core/src/test/scala/fr/acinq/eclair/integration/PerformanceIntegrationSpec.scala

@@ -51,13 +51,22 @@ class PerformanceIntegrationSpec extends IntegrationSpec {
     val eventListener = TestProbe()
     nodes.values.foreach(_.system.eventStream.subscribe(eventListener.ref, classOf[ChannelStateChanged]))
 
+    connect(nodes("A"), nodes("B"), 100_000_000 sat, 0 msat)
+    connect(nodes("A"), nodes("B"), 100_000_000 sat, 0 msat)
+    connect(nodes("A"), nodes("B"), 100_000_000 sat, 0 msat)
+    connect(nodes("A"), nodes("B"), 100_000_000 sat, 0 msat)
+    connect(nodes("A"), nodes("B"), 100_000_000 sat, 0 msat)
+    connect(nodes("A"), nodes("B"), 100_000_000 sat, 0 msat)
+    connect(nodes("A"), nodes("B"), 100_000_000 sat, 0 msat)
     connect(nodes("A"), nodes("B"), 100_000_000 sat, 0 msat)
 
     // confirming the funding tx
     generateBlocks(6)
 
     within(60 seconds) {
       eventListener.expectMsgType[ChannelStateChanged](60 seconds).currentState == NORMAL
+      eventListener.expectMsgType[ChannelStateChanged](60 seconds).currentState == NORMAL
+      eventListener.expectMsgType[ChannelStateChanged](60 seconds).currentState == NORMAL
     }
   }
 
@@ -67,7 +76,7 @@ class PerformanceIntegrationSpec extends IntegrationSpec {
     awaitCond({
       sender.send(nodes("A").router, Router.GetRoutingState)
       val routingState = sender.expectMsgType[Router.RoutingState]
-      routingState.channels.nonEmpty
+      routingState.channels.size == 8
     }, 60 seconds)
   }