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/**
* Copyright (C) 2020-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#include "mongo/base/dependency_graph.h"
#include <algorithm>
#include <fmt/format.h>
#include <fmt/ranges.h>
#include <iostream>
#include <iterator>
#include <random>
#include <sstream>
#include "mongo/util/assert_util.h"
#include "mongo/util/string_map.h"
namespace mongo {
void DependencyGraph::addNode(std::string name,
std::vector<std::string> prerequisites,
std::vector<std::string> dependents,
std::unique_ptr<Payload> payload) {
if (!payload) {
struct DummyPayload : Payload {};
payload = std::make_unique<DummyPayload>();
}
auto& newNode = _nodes[name];
uassert(ErrorCodes::Error(50999), name, !newNode.payload); // collision
for (auto& otherNode : prerequisites)
newNode.prerequisites.insert(otherNode);
for (auto& otherNode : dependents)
_nodes[otherNode].prerequisites.insert(name);
newNode.payload = std::move(payload);
}
namespace {
using namespace fmt::literals;
template <typename Seq>
void strAppendJoin(std::string& out, StringData separator, const Seq& sequence) {
StringData currSep;
for (StringData str : sequence) {
out.append(currSep.rawData(), currSep.size());
out.append(str.rawData(), str.size());
currSep = separator;
}
}
// In the case of a cycle, copy the cycle node names into `*cycle`.
template <typename Iter>
void throwGraphContainsCycle(Iter first, Iter last, std::vector<std::string>* cycle) {
std::vector<std::string> names;
std::transform(first, last, std::back_inserter(names), [](auto& e) { return e->name(); });
if (cycle)
*cycle = names;
names.push_back((*first)->name());
uasserted(ErrorCodes::GraphContainsCycle,
format(FMT_STRING("Cycle in dependency graph: {}"), fmt::join(names, " -> ")));
}
} // namespace
std::vector<std::string> DependencyGraph::topSort(std::vector<std::string>* cycle) const {
// Topological sort via repeated depth-first traversal.
// All nodes must have an initFn before running topSort, or we return BadValue.
struct Element {
const std::string& name() const {
return nodeIter->first;
}
stdx::unordered_map<std::string, Node>::const_iterator nodeIter;
std::vector<Element*> children;
std::vector<Element*>::iterator membership; // Position of this in `elements`.
};
std::vector<Element> elementsStore;
std::vector<Element*> elements;
// Swap the pointers in the `elements` vector that point to `a` and `b`.
// Update their 'membership' data members to reflect the change.
auto swapPositions = [](Element& a, Element& b) {
using std::swap;
swap(*a.membership, *b.membership);
swap(a.membership, b.membership);
};
elementsStore.reserve(_nodes.size());
for (auto iter = _nodes.begin(); iter != _nodes.end(); ++iter) {
uassert(ErrorCodes::BadValue,
"node {} was mentioned but never added"_format(iter->first),
iter->second.payload);
elementsStore.push_back(Element{iter});
}
// Wire up all the child relationships by pointer rather than by string names.
{
StringMap<Element*> byName;
for (Element& e : elementsStore)
byName[e.name()] = &e;
for (Element& element : elementsStore) {
const auto& prereqs = element.nodeIter->second.prerequisites;
std::transform(prereqs.begin(),
prereqs.end(),
std::back_inserter(element.children),
[&](StringData childName) {
auto iter = byName.find(childName);
uassert(ErrorCodes::BadValue,
"node {} depends on missing node {}"_format(
element.nodeIter->first, childName),
iter != byName.end());
return iter->second;
});
}
}
elements.reserve(_nodes.size());
std::transform(elementsStore.begin(),
elementsStore.end(),
std::back_inserter(elements),
[](auto& e) { return &e; });
// Shuffle the inputs to improve test coverage of undeclared dependencies.
{
std::random_device slowSeedGen;
std::mt19937 generator(slowSeedGen());
std::shuffle(elements.begin(), elements.end(), generator);
for (Element* e : elements)
std::shuffle(e->children.begin(), e->children.end(), generator);
}
// Initialize all the `membership` iterators. Must only happen after shuffle.
for (auto iter = elements.begin(); iter != elements.end(); ++iter)
(*iter)->membership = iter;
// The `elements` sequence is divided into 3 regions:
// elements: [ sorted | unsorted | stack ]
// unsortedBegin => [ ) <= unsortedEnd
// Each element of the stack region is a prerequisite of its neighbor to the right. Through
// 'swapPositions' calls and boundary increments, elements will transition from unsorted to
// stack to sorted. The unsorted region shinks to ultimately become an empty region on the
// right. No other moves are permitted.
auto unsortedBegin = elements.begin();
auto unsortedEnd = elements.end();
while (unsortedBegin != elements.end()) {
if (unsortedEnd == elements.end()) {
// The stack is empty but there's more work to do. Grow the stack region to enclose
// the rightmost unsorted element. Equivalent to pushing it.
--unsortedEnd;
}
auto top = unsortedEnd;
auto& children = (*top)->children;
if (!children.empty()) {
Element* picked = children.back();
children.pop_back();
if (picked->membership < unsortedBegin)
continue;
if (picked->membership >= unsortedEnd) { // O(1) cycle detection
throwGraphContainsCycle(unsortedEnd, elements.end(), cycle);
}
swapPositions(**--unsortedEnd, *picked); // unsorted push to stack
continue;
}
swapPositions(**unsortedEnd++, **unsortedBegin++); // pop from stack to sorted
}
std::vector<std::string> sortedNames;
sortedNames.reserve(_nodes.size());
std::transform(elements.begin(),
elements.end(),
std::back_inserter(sortedNames),
[](const Element* e) { return e->name(); });
return sortedNames;
}
DependencyGraph::Payload* DependencyGraph::find(const std::string& name) {
auto iter = _nodes.find(name);
return (iter == _nodes.end()) ? nullptr : iter->second.payload.get();
}
} // namespace mongo
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