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