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/* Copyright 2012 10gen Inc.
*
* 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.
*/
#include "mongo/base/initializer_dependency_graph.h"
#include <algorithm>
#include <iterator>
#include <sstream>
namespace mongo {
InitializerDependencyGraph::InitializerDependencyGraph() {}
InitializerDependencyGraph::~InitializerDependencyGraph() {}
Status InitializerDependencyGraph::addInitializer(const std::string& name,
const InitializerFunction& fn,
const std::vector<std::string>& prerequisites,
const std::vector<std::string>& dependents) {
if (!fn)
return Status(ErrorCodes::BadValue, "Illegal to supply a NULL function");
NodeData& newNode = _nodes[name];
if (newNode.fn) {
return Status(ErrorCodes::DuplicateKey, name);
}
newNode.fn = fn;
for (size_t i = 0; i < prerequisites.size(); ++i) {
newNode.prerequisites.insert(prerequisites[i]);
}
for (size_t i = 0; i < dependents.size(); ++i) {
_nodes[dependents[i]].prerequisites.insert(name);
}
return Status::OK();
}
InitializerFunction InitializerDependencyGraph::getInitializerFunction(
const std::string& name) const {
NodeMap::const_iterator iter = _nodes.find(name);
if (iter == _nodes.end())
return InitializerFunction();
return iter->second.fn;
}
Status InitializerDependencyGraph::topSort(std::vector<std::string>* sortedNames) const {
/*
* This top-sort is implemented by performing a depth-first traversal of the dependency
* graph, once for each node. "visitedNodeNames" tracks the set of node names ever visited,
* and it is used to prune each DFS. A node that has been visited once on any DFS is never
* visited again. Complexity of this implementation is O(n+m) where "n" is the number of
* nodes and "m" is the number of prerequisite edges. Space complexity is O(n), in both
* stack space and size of the "visitedNodeNames" set.
*
* "inProgressNodeNames" is used to detect and report cycles.
*/
std::vector<std::string> inProgressNodeNames;
unordered_set<std::string> visitedNodeNames;
sortedNames->clear();
for (NodeMap::const_iterator iter = _nodes.begin(), end = _nodes.end();
iter != end; ++iter) {
Status status = recursiveTopSort(_nodes,
*iter,
&inProgressNodeNames,
&visitedNodeNames,
sortedNames);
if (Status::OK() != status)
return status;
}
return Status::OK();
}
Status InitializerDependencyGraph::recursiveTopSort(
const NodeMap& nodeMap,
const Node& currentNode,
std::vector<std::string>* inProgressNodeNames,
unordered_set<std::string>* visitedNodeNames,
std::vector<std::string>* sortedNames) {
/*
* The top sort is performed by depth-first traversal starting at each node in the
* dependency graph, short-circuited any time a node is seen that has already been visited
* in any traversal. "visitedNodeNames" is the set of nodes that have been successfully
* visited, while "inProgressNodeNames" are nodes currently in the exploration chain. This
* structure is kept explicitly to facilitate cycle detection.
*
* This function implements a depth-first traversal, and is called once for each node in the
* graph by topSort(), above.
*/
if ((*visitedNodeNames).count(currentNode.first))
return Status::OK();
if (!currentNode.second.fn)
return Status(ErrorCodes::BadValue, currentNode.first);
inProgressNodeNames->push_back(currentNode.first);
std::vector<std::string>::iterator firstOccurence = std::find(
inProgressNodeNames->begin(), inProgressNodeNames->end(), currentNode.first);
if (firstOccurence + 1 != inProgressNodeNames->end()) {
sortedNames->clear();
std::copy(firstOccurence, inProgressNodeNames->end(), std::back_inserter(*sortedNames));
std::ostringstream os;
os << "Cycle in dependendcy graph: " << sortedNames->at(0);
for (size_t i = 1; i < sortedNames->size(); ++i)
os << " -> " << sortedNames->at(i);
return Status(ErrorCodes::GraphContainsCycle, os.str());
}
for (unordered_set<std::string>::const_iterator
iter = currentNode.second.prerequisites.begin(),
end = currentNode.second.prerequisites.end();
iter != end; ++iter) {
NodeMap::const_iterator nextNode = nodeMap.find(*iter);
if (nextNode == nodeMap.end())
return Status(ErrorCodes::BadValue, *iter);
Status status = recursiveTopSort(nodeMap,
*nextNode,
inProgressNodeNames,
visitedNodeNames,
sortedNames);
if (Status::OK() != status)
return status;
}
sortedNames->push_back(currentNode.first);
if (inProgressNodeNames->back() != currentNode.first)
return Status(ErrorCodes::InternalError, "inProgressNodeNames stack corrupt");
inProgressNodeNames->pop_back();
visitedNodeNames->insert(currentNode.first);
return Status::OK();
}
} // namespace mongo
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