AU: Cut cycles even more aggressively, log progress of cutting

cycle_breaker.cc

 // Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "update_engine/cycle_breaker.h"
+#include <inttypes.h>
 #include <set>
 #include <utility>
+#include "base/string_util.h"
 #include "update_engine/graph_utils.h"
 #include "update_engine/tarjan.h"
 #include "update_engine/utils.h"
 
 using std::make_pair;
 using std::set;
 using std::vector;
 
 namespace chromeos_update_engine {
 
@@ skipping 40 matching lines @@
         if (utils::MapContainsKey(subgraph_[*it].out_edges, *jt))
           subgraph_[*it].subgraph_edges.insert(*jt);
       }        
     }
 
     current_vertex_ = i;
     blocked_.clear();
     blocked_.resize(subgraph_.size());
     blocked_graph_.clear();
     blocked_graph_.resize(subgraph_.size());
-    Circuit(current_vertex_);
+    Circuit(current_vertex_, 0);
   }
   
   out_cut_edges->swap(cut_edges_);
   DCHECK(stack_.empty());
 }
 
+static const size_t kMaxEdgesToConsider = 2;
+
 void CycleBreaker::HandleCircuit() {
   stack_.push_back(current_vertex_);
   CHECK_GE(stack_.size(), 2);
   Edge min_edge = make_pair(stack_[0], stack_[1]);
   uint64_t min_edge_weight = kuint64max;
-  const int kMaxEdgesToConsider = 4;
-  int edges_considered = 0;
+  size_t edges_considered = 0;
   for (vector<Vertex::Index>::const_iterator it = stack_.begin();
        it != (stack_.end() - 1); ++it) {
     Edge edge = make_pair(*it, *(it + 1));
     if (cut_edges_.find(edge) != cut_edges_.end()) {
       stack_.pop_back();
       return;
     }
     uint64_t edge_weight = graph_utils::EdgeWeight(subgraph_, edge);
     if (edge_weight < min_edge_weight) {
       min_edge_weight = edge_weight;
@@ skipping 23 matching lines @@
   for (std::vector<Vertex::Index>::const_iterator it = ++stack_.begin(),
         e = stack_.end(); it != e; ++it) {
     Edge edge = make_pair(*(it - 1), *it);
     if (utils::SetContainsKey(cut_edges_, edge)) {
       return true;
     }
   }
   return false;
 }
 
-bool CycleBreaker::Circuit(Vertex::Index vertex) {
+bool CycleBreaker::Circuit(Vertex::Index vertex, Vertex::Index depth) {
   // "vertex" was "v" in the original paper.
   bool found = false;  // Was "f" in the original paper.
   stack_.push_back(vertex);
   blocked_[vertex] = true;
+  {
+    static int counter = 0;
+    counter++;
+    if (counter == 10000) {
+      counter = 0;
+      std::string stack_str;
+      for (vector<Vertex::Index>::const_iterator it = stack_.begin();
+           it != stack_.end(); ++it) {
+        stack_str += StringPrintf("%lu -> ",
+                                  static_cast<long unsigned int>(*it));
+      }
+      LOG(INFO) << "stack: " << stack_str;
+    }
+  }
 
   for (Vertex::SubgraphEdgeMap::iterator w =
            subgraph_[vertex].subgraph_edges.begin();
        w != subgraph_[vertex].subgraph_edges.end(); ++w) {
     if (*w == current_vertex_) {
       // The original paper called for printing stack_ followed by
       // current_vertex_ here, which is a cycle. Instead, we call
       // HandleCircuit() to break it.
       HandleCircuit();
       found = true;
     } else if (!blocked_[*w]) {
-      if (Circuit(*w)) {
+      if (Circuit(*w, depth + 1)) {
         found = true;
-        if (StackContainsCutEdge())
+        if ((depth > kMaxEdgesToConsider) || StackContainsCutEdge())
           break;
       }
     }
   }
 
   if (found) {
     Unblock(vertex);
   } else {
     for (Vertex::SubgraphEdgeMap::iterator w =
              subgraph_[vertex].subgraph_edges.begin();
          w != subgraph_[vertex].subgraph_edges.end(); ++w) {
       if (blocked_graph_[*w].out_edges.find(vertex) ==
           blocked_graph_[*w].out_edges.end()) {
         blocked_graph_[*w].out_edges.insert(make_pair(vertex,
                                                       EdgeProperties()));
       }
     }
   }
   CHECK_EQ(vertex, stack_.back());
   stack_.pop_back();
   return found;
 }
 
 }  // namespace chromeos_update_engine