upload android base code part6

android/system/core/libmemunreachable/Tarjan.h

@@ -0,0 +1,138 @@
+/*
+ * Copyright (C) 2016 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// Based on system/update_engine/payload_generator/tarjan.cc
+
+#ifndef LIBMEMUNREACHABLE_TARJAN_H_
+#define LIBMEMUNREACHABLE_TARJAN_H_
+
+#include <assert.h>
+#include <algorithm>
+
+#include "Allocator.h"
+
+namespace android {
+
+template <class T>
+class Node {
+ public:
+  allocator::set<Node<T>*> references_in;
+  allocator::set<Node<T>*> references_out;
+  size_t index;
+  size_t lowlink;
+
+  T* ptr;
+
+  Node(T* ptr, Allocator<Node> allocator)
+      : references_in(allocator), references_out(allocator), ptr(ptr){};
+  Node(Node&& rhs) = default;
+  void Edge(Node<T>* ref) {
+    references_out.emplace(ref);
+    ref->references_in.emplace(this);
+  }
+  template <class F>
+  void Foreach(F&& f) {
+    for (auto& node : references_out) {
+      f(node->ptr);
+    }
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(Node<T>);
+};
+
+template <class T>
+using Graph = allocator::vector<Node<T>*>;
+
+template <class T>
+using SCC = allocator::vector<Node<T>*>;
+
+template <class T>
+using SCCList = allocator::vector<SCC<T>>;
+
+template <class T>
+class TarjanAlgorithm {
+ public:
+  explicit TarjanAlgorithm(Allocator<void> allocator)
+      : index_(0), stack_(allocator), components_(allocator) {}
+
+  void Execute(Graph<T>& graph, SCCList<T>& out);
+
+ private:
+  static constexpr size_t UNDEFINED_INDEX = static_cast<size_t>(-1);
+  void Tarjan(Node<T>* vertex, Graph<T>& graph);
+
+  size_t index_;
+  allocator::vector<Node<T>*> stack_;
+  SCCList<T> components_;
+};
+
+template <class T>
+void TarjanAlgorithm<T>::Execute(Graph<T>& graph, SCCList<T>& out) {
+  stack_.clear();
+  components_.clear();
+  index_ = 0;
+  for (auto& it : graph) {
+    it->index = UNDEFINED_INDEX;
+    it->lowlink = UNDEFINED_INDEX;
+  }
+
+  for (auto& it : graph) {
+    if (it->index == UNDEFINED_INDEX) {
+      Tarjan(it, graph);
+    }
+  }
+  out.swap(components_);
+}
+
+template <class T>
+void TarjanAlgorithm<T>::Tarjan(Node<T>* vertex, Graph<T>& graph) {
+  assert(vertex->index == UNDEFINED_INDEX);
+  vertex->index = index_;
+  vertex->lowlink = index_;
+  index_++;
+  stack_.push_back(vertex);
+  for (auto& it : vertex->references_out) {
+    Node<T>* vertex_next = it;
+    if (vertex_next->index == UNDEFINED_INDEX) {
+      Tarjan(vertex_next, graph);
+      vertex->lowlink = std::min(vertex->lowlink, vertex_next->lowlink);
+    } else if (std::find(stack_.begin(), stack_.end(), vertex_next) != stack_.end()) {
+      vertex->lowlink = std::min(vertex->lowlink, vertex_next->index);
+    }
+  }
+  if (vertex->lowlink == vertex->index) {
+    SCC<T> component{components_.get_allocator()};
+    Node<T>* other_vertex;
+    do {
+      other_vertex = stack_.back();
+      stack_.pop_back();
+      component.push_back(other_vertex);
+    } while (other_vertex != vertex && !stack_.empty());
+
+    components_.emplace_back(component);
+  }
+}
+
+template <class T>
+void Tarjan(Graph<T>& graph, SCCList<T>& out) {
+  TarjanAlgorithm<T> tarjan{graph.get_allocator()};
+  tarjan.Execute(graph, out);
+}
+
+}  // namespace android
+
+#endif  // LIBMEMUNREACHABLE_TARJAN_H_