Codechange: [Linkgraph] Skip MCF source node Dijkstra when all demand satisfied

MCF Dijkstra iterations are executed for all source nodes in a round-robin order.
Source nodes typically require different numbers of MCF Dijkstra iterations
to satisfy all of their demand.
This change is to avoid performing MCF Dijkstra iterations on source nodes which
have already been fully satisfied.

src/linkgraph/mcf.cpp

@@ -494,13 +494,17 @@ MCF1stPass::MCF1stPass(LinkGraphJob &job) : MultiCommodityFlow(job)
 	uint size = job.Size();
 	uint accuracy = job.Settings().accuracy;
 	bool more_loops;
+	std::vector<bool> finished_sources(size);
 
 	do {
 		more_loops = false;
 		for (NodeID source = 0; source < size; ++source) {
+			if (finished_sources[source]) continue;
+
 			/* First saturate the shortest paths. */
 			this->Dijkstra<DistanceAnnotation, GraphEdgeIterator>(source, paths);
 
+			bool source_demand_left = false;
 			for (NodeID dest = 0; dest < size; ++dest) {
 				Edge edge = job[source][dest];
 				if (edge.UnsatisfiedDemand() > 0) {
@@ -518,8 +522,10 @@ MCF1stPass::MCF1stPass(LinkGraphJob &job) : MultiCommodityFlow(job)
 							path->GetFreeCapacity() > INT_MIN) {
 						this->PushFlow(edge, path, accuracy, UINT_MAX);
 					}
+					if (edge.UnsatisfiedDemand() > 0) source_demand_left = true;
 				}
 			}
+			finished_sources[source] = !source_demand_left;
 			this->CleanupPaths(source, paths);
 		}
 	} while (more_loops || this->EliminateCycles());
@@ -537,18 +543,27 @@ MCF2ndPass::MCF2ndPass(LinkGraphJob &job) : MultiCommodityFlow(job)
 	uint size = job.Size();
 	uint accuracy = job.Settings().accuracy;
 	bool demand_left = true;
+	std::vector<bool> finished_sources(size);
 	while (demand_left) {
 		demand_left = false;
 		for (NodeID source = 0; source < size; ++source) {
+			if (finished_sources[source]) continue;
+
 			this->Dijkstra<CapacityAnnotation, FlowEdgeIterator>(source, paths);
+
+			bool source_demand_left = false;
 			for (NodeID dest = 0; dest < size; ++dest) {
 				Edge edge = this->job[source][dest];
 				Path *path = paths[dest];
 				if (edge.UnsatisfiedDemand() > 0 && path->GetFreeCapacity() > INT_MIN) {
 					this->PushFlow(edge, path, accuracy, UINT_MAX);
-					if (edge.UnsatisfiedDemand() > 0) demand_left = true;
+					if (edge.UnsatisfiedDemand() > 0) {
+						demand_left = true;
+						source_demand_left = true;
+					}
 				}
 			}
+			finished_sources[source] = !source_demand_left;
 			this->CleanupPaths(source, paths);
 		}
 	}