1 //
2 // Copyright (C) 2010 The Android Open Source Project
3 //
4 // Licensed under the Apache License, Version 2.0 (the "License");
5 // you may not use this file except in compliance with the License.
6 // You may obtain a copy of the License at
7 //
8 //      http://www.apache.org/licenses/LICENSE-2.0
9 //
10 // Unless required by applicable law or agreed to in writing, software
11 // distributed under the License is distributed on an "AS IS" BASIS,
12 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 // See the License for the specific language governing permissions and
14 // limitations under the License.
15 //
16 #include "update_engine/payload_generator/tarjan.h"
17 
18 #include <algorithm>
19 #include <vector>
20 
21 #include <base/logging.h>
22 
23 #include "update_engine/common/utils.h"
24 
25 using std::min;
26 using std::vector;
27 
28 namespace chromeos_update_engine {
29 
30 namespace {
31 const vector<Vertex>::size_type kInvalidIndex = -1;
32 }
33 
34 void TarjanAlgorithm::Execute(Vertex::Index vertex,
35                               Graph* graph,
36                               vector<Vertex::Index>* out) {
37   stack_.clear();
38   components_.clear();
39   index_ = 0;
40   for (Graph::iterator it = graph->begin(); it != graph->end(); ++it)
41     it->index = it->lowlink = kInvalidIndex;
42   required_vertex_ = vertex;
43 
44   Tarjan(vertex, graph);
45   if (!components_.empty())
46     out->swap(components_[0]);
47 }
48 
49 void TarjanAlgorithm::Tarjan(Vertex::Index vertex, Graph* graph) {
50   CHECK_EQ((*graph)[vertex].index, kInvalidIndex);
51   (*graph)[vertex].index = index_;
52   (*graph)[vertex].lowlink = index_;
53   index_++;
54   stack_.push_back(vertex);
55   for (Vertex::EdgeMap::iterator it = (*graph)[vertex].out_edges.begin();
56        it != (*graph)[vertex].out_edges.end(); ++it) {
57     Vertex::Index vertex_next = it->first;
58     if ((*graph)[vertex_next].index == kInvalidIndex) {
59       Tarjan(vertex_next, graph);
60       (*graph)[vertex].lowlink = min((*graph)[vertex].lowlink,
61                                      (*graph)[vertex_next].lowlink);
62     } else if (utils::VectorContainsValue(stack_, vertex_next)) {
63       (*graph)[vertex].lowlink = min((*graph)[vertex].lowlink,
64                                      (*graph)[vertex_next].index);
65     }
66   }
67   if ((*graph)[vertex].lowlink == (*graph)[vertex].index) {
68     vector<Vertex::Index> component;
69     Vertex::Index other_vertex;
70     do {
71       other_vertex = stack_.back();
72       stack_.pop_back();
73       component.push_back(other_vertex);
74     } while (other_vertex != vertex && !stack_.empty());
75 
76     if (utils::VectorContainsValue(component, required_vertex_)) {
77       components_.resize(components_.size() + 1);
78       component.swap(components_.back());
79     }
80   }
81 }
82 
83 }  // namespace chromeos_update_engine
84