(svn r25963) -Fix [FS#5758]: Mixtures of old and new flows could create cycles.

src/linkgraph/linkgraphjob.cpp

@@ -72,7 +72,11 @@ LinkGraphJob::~LinkGraphJob()
 					st2->goods[this->Cargo()].node != it->first ||
 					(*lg)[node_id][it->first].LastUpdate() == INVALID_DATE) {
 				/* Edge has been removed. Delete flows. */
-				flows.DeleteFlows(to);
+				StationIDStack erased = flows.DeleteFlows(to);
+				/* Delete old flows for source stations which have been deleted
+				 * from the new flows. This avoids flow cycles between old and
+				 * new flows. */
+				while (!erased.IsEmpty()) ge.flows.erase(erased.Pop());
 			} else if ((*lg)[node_id][it->first].LastUnrestrictedUpdate() == INVALID_DATE) {
 				/* Edge is fully restricted. */
 				flows.RestrictFlows(to);

src/station_base.h

@@ -148,7 +148,7 @@ class FlowStatMap : public std::map<StationID, FlowStat> {
 public:
 	void AddFlow(StationID origin, StationID via, uint amount);
 	void PassOnFlow(StationID origin, StationID via, uint amount);
-	void DeleteFlows(StationID via);
+	StationIDStack DeleteFlows(StationID via);
 	void RestrictFlows(StationID via);
 	void ReleaseFlows(StationID via);
 	void FinalizeLocalConsumption(StationID self);

src/station_cmd.cpp

@@ -4352,18 +4352,23 @@ void FlowStatMap::FinalizeLocalConsumption(StationID self)
 /**
  * Delete all flows at a station for specific cargo and destination.
  * @param via Remote station of flows to be deleted.
+ * @return IDs of source stations for which the complete FlowStat, not only a
+ *         share, has been erased.
  */
-void FlowStatMap::DeleteFlows(StationID via)
+StationIDStack FlowStatMap::DeleteFlows(StationID via)
 {
+	StationIDStack ret;
 	for (FlowStatMap::iterator f_it = this->begin(); f_it != this->end();) {
 		FlowStat &s_flows = f_it->second;
 		s_flows.ChangeShare(via, INT_MIN);
 		if (s_flows.GetShares()->empty()) {
+			ret.Push(f_it->first);
 			this->erase(f_it++);
 		} else {
 			++f_it;
 		}
 	}
+	return ret;
 }
 
 /**