[simgrid.git] / src / mc / explo / odpor / WakeupTree.cpp

/* Copyright (c) 2008-2023. The SimGrid Team. All rights reserved.          */

/* This program is free software; you can redistribute it and/or modify it
 * under the terms of the license (GNU LGPL) which comes with this package. */

#include "src/mc/explo/odpor/WakeupTree.hpp"
#include "src/mc/explo/odpor/Execution.hpp"
#include "xbt/asserts.h"
#include "xbt/string.hpp"

#include <algorithm>
#include <exception>
#include <memory>
#include <queue>

namespace simgrid::mc::odpor {

void WakeupTreeNode::add_child(WakeupTreeNode* node)
{
  this->children_.push_back(node);
  node->parent_ = this;
}

PartialExecution WakeupTreeNode::get_sequence() const
{
  // TODO: Prevent having to compute this at the node level
  // and instead track this with the iterator
  PartialExecution seq_;
  const WakeupTreeNode* cur_node = this;
  while (cur_node != nullptr && not cur_node->is_root()) {
    seq_.push_front(cur_node->action_);
    cur_node = cur_node->parent_;
  }
  return seq_;
}

void WakeupTreeNode::detatch_from_parent()
{
  if (parent_ != nullptr) {
    // TODO: There may be a better method
    // of keeping track of a node's reference to
    // its parent, perhaps keeping track
    // of a std::list<>::iterator instead.
    // This would allow us to detach a node
    // in O(1) instead of O(|children|) time
    parent_->children_.remove(this);
  }
}

WakeupTree::WakeupTree() : WakeupTree(std::make_unique<WakeupTreeNode>()) {}
WakeupTree::WakeupTree(std::unique_ptr<WakeupTreeNode> root) : root_(root.get())
{
  this->insert_node(std::move(root));
}

std::vector<std::string> WakeupTree::get_single_process_texts() const
{
  std::vector<std::string> trace;
  for (const auto* child : root_->children_) {
    const auto t = child->get_action();
    auto message = xbt::string_printf("Actor %ld: %s", t->aid_, t->to_string(true).c_str());
    trace.emplace_back(std::move(message));
  }
  return trace;
}

std::optional<aid_t> WakeupTree::get_min_single_process_actor() const
{
  if (const auto node = get_min_single_process_node(); node.has_value()) {
    return node.value()->get_actor();
  }
  return std::nullopt;
}

std::optional<WakeupTreeNode*> WakeupTree::get_min_single_process_node() const
{
  if (empty()) {
    return std::nullopt;
  }
  // INVARIANT: The induced post-order relation always places children
  // in order before the parent. The list of children maintained by
  // each node represents that ordering, and the first child of
  // the root is by definition the smallest of the single-process nodes
  xbt_assert(not this->root_->children_.empty(), "What the");
  return this->root_->children_.front();
}

WakeupTree WakeupTree::make_subtree_rooted_at(WakeupTreeNode* root)
{
  // Perform a BFS search to perform a deep copy of the portion
  // of the tree underneath and including `root`. Note that `root`
  // is contained within the context of a *different* wakeup tree;
  // hence, we have to be careful to update each node's children
  // appropriately
  auto subtree = WakeupTree();

  std::list<std::pair<WakeupTreeNode*, WakeupTreeNode*>> frontier{std::make_pair(root, subtree.root_)};
  while (not frontier.empty()) {
    auto [node_in_other_tree, subtree_equivalent] = frontier.front();
    frontier.pop_front();

    // For each child of the node corresponding to that in `subtree`,
    // make clones of each of its children and add them to `frontier`
    // to that their children are added, and so on.
    for (WakeupTreeNode* child_in_other_tree : node_in_other_tree->get_ordered_children()) {
      WakeupTreeNode* child_equivalent = subtree.make_node(child_in_other_tree->get_action());
      subtree_equivalent->add_child(child_equivalent);
      frontier.push_back(std::make_pair(child_in_other_tree, child_equivalent));
    }
  }
  return subtree;
}

void WakeupTree::remove_subtree_rooted_at(WakeupTreeNode* root)
{
  if (not contains(root)) {
    throw std::invalid_argument("Attempting to remove a subtree pivoted from a node "
                                "that is not contained in this wakeup tree");
  }

  std::list<WakeupTreeNode*> subtree_contents{root};
  std::list<WakeupTreeNode*> frontier{root};
  while (not frontier.empty()) {
    const auto* node = frontier.front();
    frontier.pop_front();
    for (const auto& child : node->get_ordered_children()) {
      frontier.push_back(child);
      subtree_contents.push_back(child);
    }
  }

  // After having found each node with BFS, now we can
  // remove them. This prevents the "joys" of iteration during mutation.
  // We also remove the `root` from being referenced by its own parent (since
  // it will soon be destroyed)
  root->detatch_from_parent();
  for (WakeupTreeNode* node_to_remove : subtree_contents) {
    this->remove_node(node_to_remove);
  }
}

void WakeupTree::remove_min_single_process_subtree()
{
  if (const auto node = get_min_single_process_node(); node.has_value()) {
    remove_subtree_rooted_at(node.value());
  }
}

bool WakeupTree::contains(const WakeupTreeNode* node) const
{
  return std::find_if(this->nodes_.begin(), this->nodes_.end(), [=](const auto& pair) { return pair.first == node; }) !=
         this->nodes_.end();
}

WakeupTreeNode* WakeupTree::make_node(std::shared_ptr<Transition> u)
{
  auto node                 = std::make_unique<WakeupTreeNode>(std::move(u));
  auto* node_handle         = node.get();
  this->nodes_[node_handle] = std::move(node);
  return node_handle;
}

void WakeupTree::insert_node(std::unique_ptr<WakeupTreeNode> node)
{
  auto* node_handle         = node.get();
  this->nodes_[node_handle] = std::move(node);
}

void WakeupTree::remove_node(WakeupTreeNode* node)
{
  this->nodes_.erase(node);
}

WakeupTree::InsertionResult WakeupTree::insert(const Execution& E, const PartialExecution& w)
{
  // See section 6.2 of Abdulla. et al.'s 2017 ODPOR paper for details

  // Find the first node `v` in the tree such that
  // `v ~_[E] w` and `v`  is not a leaf node
  for (WakeupTreeNode* node : *this) {
    if (const auto shortest_sequence = E.get_shortest_odpor_sq_subset_insertion(node->get_sequence(), w);
        shortest_sequence.has_value()) {
      // Insert the sequence as a child of `node`, but only
      // if the node is not already a leaf
      if (not node->is_leaf() || node == this->root_) {
        // NOTE: It's entirely possible that the shortest
        // sequence we are inserting is empty. Consider the
        // following two cases:
        //
        // 1. `w` is itself empty. Evidently, insertion succeeds but nothing needs
        // to happen
        //
        // 2. a leaf node in the tree already contains `w` exactly.
        // In this case, the empty `w'` returned (viz. `shortest_seq`)
        // such that `w [=_[E] v.w'` would be empty
        this->insert_sequence_after(node, shortest_sequence.value());
        return node == this->root_ ? InsertionResult::root : InsertionResult::interior_node;
      }
      // Since we're following the post-order traversal of the tree,
      // the first such node we see is the smallest w.r.t "<"
      return InsertionResult::leaf;
    }
  }
  xbt_die("Insertion should always succeed with the root node (which contains no "
          "prior execution). If we've reached this point, this implies either that "
          "the wakeup tree traversal is broken or that computation of the shortest "
          "sequence to insert into the tree is broken");
}

void WakeupTree::insert_sequence_after(WakeupTreeNode* node, const PartialExecution& w)
{
  WakeupTreeNode* cur_node = node;
  for (const auto& w_i : w) {
    WakeupTreeNode* new_node = this->make_node(w_i);
    cur_node->add_child(new_node);
    cur_node = new_node;
  }
}

} // namespace simgrid::mc::odpor