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 namespace android {
28
29 template <class T>
30 class Node {
31 public:
32 allocator::set<Node<T>*> references_in;
33 allocator::set<Node<T>*> references_out;
34 size_t index;
35 size_t lowlink;
36
37 T* ptr;
38
Node(T * ptr,Allocator<Node> allocator)39 Node(T* ptr, Allocator<Node> allocator)
40 : references_in(allocator), references_out(allocator), ptr(ptr){};
41 Node(Node&& rhs) noexcept = default;
Edge(Node<T> * ref)42 void Edge(Node<T>* ref) {
43 references_out.emplace(ref);
44 ref->references_in.emplace(this);
45 }
46 template <class F>
Foreach(F && f)47 void Foreach(F&& f) {
48 for (auto& node : references_out) {
49 f(node->ptr);
50 }
51 }
52
53 private:
54 DISALLOW_COPY_AND_ASSIGN(Node<T>);
55 };
56
57 template <class T>
58 using Graph = allocator::vector<Node<T>*>;
59
60 template <class T>
61 using SCC = allocator::vector<Node<T>*>;
62
63 template <class T>
64 using SCCList = allocator::vector<SCC<T>>;
65
66 template <class T>
67 class TarjanAlgorithm {
68 public:
TarjanAlgorithm(Allocator<void> allocator)69 explicit TarjanAlgorithm(Allocator<void> allocator)
70 : index_(0), stack_(allocator), components_(allocator) {}
71
72 void Execute(Graph<T>& graph, SCCList<T>& out);
73
74 private:
75 static constexpr size_t UNDEFINED_INDEX = static_cast<size_t>(-1);
76 void Tarjan(Node<T>* vertex, Graph<T>& graph);
77
78 size_t index_;
79 allocator::vector<Node<T>*> stack_;
80 SCCList<T> components_;
81 };
82
83 template <class T>
Execute(Graph<T> & graph,SCCList<T> & out)84 void TarjanAlgorithm<T>::Execute(Graph<T>& graph, SCCList<T>& out) {
85 stack_.clear();
86 components_.clear();
87 index_ = 0;
88 for (auto& it : graph) {
89 it->index = UNDEFINED_INDEX;
90 it->lowlink = UNDEFINED_INDEX;
91 }
92
93 for (auto& it : graph) {
94 if (it->index == UNDEFINED_INDEX) {
95 Tarjan(it, graph);
96 }
97 }
98 out.swap(components_);
99 }
100
101 template <class T>
Tarjan(Node<T> * vertex,Graph<T> & graph)102 void TarjanAlgorithm<T>::Tarjan(Node<T>* vertex, Graph<T>& graph) {
103 assert(vertex->index == UNDEFINED_INDEX);
104 vertex->index = index_;
105 vertex->lowlink = index_;
106 index_++;
107 stack_.push_back(vertex);
108 for (auto& it : vertex->references_out) {
109 Node<T>* vertex_next = it;
110 if (vertex_next->index == UNDEFINED_INDEX) {
111 Tarjan(vertex_next, graph);
112 vertex->lowlink = std::min(vertex->lowlink, vertex_next->lowlink);
113 } else if (std::find(stack_.begin(), stack_.end(), vertex_next) != stack_.end()) {
114 vertex->lowlink = std::min(vertex->lowlink, vertex_next->index);
115 }
116 }
117 if (vertex->lowlink == vertex->index) {
118 SCC<T> component{components_.get_allocator()};
119 Node<T>* other_vertex;
120 do {
121 other_vertex = stack_.back();
122 stack_.pop_back();
123 component.push_back(other_vertex);
124 } while (other_vertex != vertex && !stack_.empty());
125
126 components_.emplace_back(component);
127 }
128 }
129
130 template <class T>
Tarjan(Graph<T> & graph,SCCList<T> & out)131 void Tarjan(Graph<T>& graph, SCCList<T>& out) {
132 TarjanAlgorithm<T> tarjan{graph.get_allocator()};
133 tarjan.Execute(graph, out);
134 }
135
136 } // namespace android
137
138 #endif // LIBMEMUNREACHABLE_TARJAN_H_
139