1 /*
2 * Copyright (C) 2016 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
17 // Based on system/update_engine/payload_generator/tarjan.cc
18
19 #ifndef LIBMEMUNREACHABLE_TARJAN_H_
20 #define LIBMEMUNREACHABLE_TARJAN_H_
21
22 #include <assert.h>
23 #include <algorithm>
24
25 #include "Allocator.h"
26
27 template<class T>
28 class Node {
29 public:
30 allocator::set<Node<T>*> references_in;
31 allocator::set<Node<T>*> references_out;
32 size_t index;
33 size_t lowlink;
34
35 T* ptr;
36
Node(T * ptr,Allocator<Node> allocator)37 Node(T* ptr, Allocator<Node> allocator) : references_in(allocator), references_out(allocator),
38 ptr(ptr) {};
39 Node(Node&& rhs) = default;
Edge(Node<T> * ref)40 void Edge(Node<T>* ref) {
41 references_out.emplace(ref);
42 ref->references_in.emplace(this);
43 }
44 template<class F>
Foreach(F && f)45 void Foreach(F&& f) {
46 for (auto& node: references_out) {
47 f(node->ptr);
48 }
49 }
50 private:
51 DISALLOW_COPY_AND_ASSIGN(Node<T>);
52 };
53
54 template<class T>
55 using Graph = allocator::vector<Node<T>*>;
56
57 template<class T>
58 using SCC = allocator::vector<Node<T>*>;
59
60 template<class T>
61 using SCCList = allocator::vector<SCC<T>>;
62
63 template<class T>
64 class TarjanAlgorithm {
65 public:
TarjanAlgorithm(Allocator<void> allocator)66 explicit TarjanAlgorithm(Allocator<void> allocator) : index_(0),
67 stack_(allocator), components_(allocator) {}
68
69 void Execute(Graph<T>& graph, SCCList<T>& out);
70 private:
71 static constexpr size_t UNDEFINED_INDEX = static_cast<size_t>(-1);
72 void Tarjan(Node<T>* vertex, Graph<T>& graph);
73
74 size_t index_;
75 allocator::vector<Node<T>*> stack_;
76 SCCList<T> components_;
77 };
78
79 template<class T>
Execute(Graph<T> & graph,SCCList<T> & out)80 void TarjanAlgorithm<T>::Execute(Graph<T>& graph, SCCList<T>& out) {
81 stack_.clear();
82 components_.clear();
83 index_ = 0;
84 for (auto& it: graph) {
85 it->index = UNDEFINED_INDEX;
86 it->lowlink = UNDEFINED_INDEX;
87 }
88
89 for (auto& it: graph) {
90 if (it->index == UNDEFINED_INDEX) {
91 Tarjan(it, graph);
92 }
93 }
94 out.swap(components_);
95 }
96
97 template<class T>
Tarjan(Node<T> * vertex,Graph<T> & graph)98 void TarjanAlgorithm<T>::Tarjan(Node<T>* vertex, Graph<T>& graph) {
99 assert(vertex->index == UNDEFINED_INDEX);
100 vertex->index = index_;
101 vertex->lowlink = index_;
102 index_++;
103 stack_.push_back(vertex);
104 for (auto& it: vertex->references_out) {
105 Node<T>* vertex_next = it;
106 if (vertex_next->index == UNDEFINED_INDEX) {
107 Tarjan(vertex_next, graph);
108 vertex->lowlink = std::min(vertex->lowlink, vertex_next->lowlink);
109 } else if (std::find(stack_.begin(), stack_.end(), vertex_next) != stack_.end()) {
110 vertex->lowlink = std::min(vertex->lowlink, vertex_next->index);
111 }
112 }
113 if (vertex->lowlink == vertex->index) {
114 SCC<T> component{components_.get_allocator()};
115 Node<T>* other_vertex;
116 do {
117 other_vertex = stack_.back();
118 stack_.pop_back();
119 component.push_back(other_vertex);
120 } while (other_vertex != vertex && !stack_.empty());
121
122 components_.emplace_back(component);
123 }
124 }
125
126 template<class T>
Tarjan(Graph<T> & graph,SCCList<T> & out)127 void Tarjan(Graph<T>& graph, SCCList<T>& out) {
128 TarjanAlgorithm<T> tarjan{graph.get_allocator()};
129 tarjan.Execute(graph, out);
130 }
131
132 #endif // LIBMEMUNREACHABLE_TARJAN_H_
133