PlanarSubgraphFast.h

Go to the documentation of this file.

 
#pragma once
 
#include <ogdf/basic/STNumbering.h>
#include <ogdf/basic/Thread.h>
#include <ogdf/basic/simple_graph_alg.h>
#include <ogdf/planarity/PlanarSubgraphModule.h>
#include <ogdf/planarity/booth_lueker/PlanarLeafKey.h>
#include <ogdf/planarity/planar_subgraph_fast/PlanarSubgraphPQTree.h>
 
#include <atomic>
 
namespace ogdf {
 
template<typename TCost>
class PlanarSubgraphFast : public PlanarSubgraphModule<TCost> {
    using BlockType = std::pair<Graph*, EdgeArray<edge>*>;
 
    class ThreadMaster {
        Array<TCost> m_bestSolution; 
        Array<List<edge>*> m_bestDelEdges; 
        int m_nBlocks; 
        const Array<BlockType>& m_block; 
        const EdgeArray<TCost>* m_pCost; 
        std::atomic<int> m_runs;
        std::mutex m_mutex; 
 
    public:
        ThreadMaster(const Array<BlockType>& block, const EdgeArray<TCost>* pCost, int runs)
            : m_bestSolution(block.size())
            , m_bestDelEdges(block.size())
            , m_nBlocks(block.size())
            , m_block(block)
            , m_pCost(pCost)
            , m_runs(runs) {
            for (int i = 0; i < m_nBlocks; ++i) {
                m_bestDelEdges[i] = nullptr;
                m_bestSolution[i] =
                        (m_block[i].first != nullptr) ? std::numeric_limits<int>::max() : 0;
            }
        }
 
        int numBlocks() const { return m_nBlocks; }
 
        const Graph& block(int i) const { return *m_block[i].first; }
 
        bool considerBlock(int i) const { return m_bestSolution[i] > 1; }
 
        List<edge>* postNewResult(int i, List<edge>* pNewDelEdges) {
            TCost newSolution = pNewDelEdges->size();
            if (m_pCost != nullptr) {
                const EdgeArray<edge>& origEdge = *m_block[i].second;
                newSolution = TCost(0);
                for (edge e : *pNewDelEdges) {
                    newSolution += (*m_pCost)[origEdge[e]];
                }
            }
 
            // m_mutex is automatically released when guard goes out of scope
            std::lock_guard<std::mutex> guard(m_mutex);
 
            if (newSolution < m_bestSolution[i]) {
                std::swap(pNewDelEdges, m_bestDelEdges[i]);
                m_bestSolution[i] = newSolution;
            }
 
            return pNewDelEdges;
        }
 
        // creates a solution for the original graph from best solutions per block
        // also deletes (intermediate) solution lists
        void buildSolution(List<edge>& delEdges) {
            for (int i = 0; i < m_nBlocks; ++i) {
                if (m_bestDelEdges[i] != nullptr) {
                    const EdgeArray<edge>& origEdge = *m_block[i].second;
                    for (edge e : *m_bestDelEdges[i]) {
                        delEdges.pushBack(origEdge[e]);
                    }
                    delete m_bestDelEdges[i];
                }
            }
        }
 
        bool getNextRun() { return --m_runs >= 0; }
    };
 
    class Worker {
        ThreadMaster* m_pMaster; // associated master
 
    public:
        Worker(ThreadMaster* pMaster) : m_pMaster(pMaster) { }
 
        ~Worker() = default;
 
        void operator()() { doWorkHelper(*m_pMaster); }
 
    private:
        Worker(const Worker& other); // = delete
        Worker& operator=(const Worker& other); // = delete
    };
 
public:
    PlanarSubgraphFast() { m_nRuns = 10; }
 
    virtual PlanarSubgraphFast* clone() const override {
        auto* res = new PlanarSubgraphFast<TCost>(*this);
        res->m_nRuns = m_nRuns;
        return res;
    }
 
    void runs(int nRuns) { m_nRuns = nRuns; }
 
    int runs() const { return m_nRuns; }
 
 
protected:
 
    virtual Module::ReturnType doCall(const Graph& G, const List<edge>& preferedEdges,
            List<edge>& delEdges, const EdgeArray<TCost>* pCost, bool preferedImplyPlanar) override {
        delEdges.clear();
 
        if (G.numberOfEdges() < 9) {
            return Module::ReturnType::Optimal;
        }
 
        // Determine Biconnected Components
        EdgeArray<int> componentID(G);
        int nBlocks = biconnectedComponents(G, componentID);
 
        // Determine edges per biconnected component
        Array<SList<edge>> blockEdges(0, nBlocks - 1);
        for (edge e : G.edges) {
            if (!e->isSelfLoop()) {
                blockEdges[componentID[e]].pushFront(e);
            }
        }
 
        // Build non-trivial blocks
        Array<BlockType> block(nBlocks);
        NodeArray<node> copyV(G, nullptr);
 
        for (int i = 0; i < nBlocks; i++) {
            if (blockEdges[i].size() < 9) {
                block[i] = BlockType((Graph*)nullptr,
                        (EdgeArray<edge>*)nullptr); // explicit casts required for VS2010
                continue;
            }
 
            Graph* bc = new Graph;
            EdgeArray<edge>* origE = new EdgeArray<edge>(*bc, nullptr);
            block[i] = BlockType(bc, origE);
 
            SList<node> marked;
            for (edge e : blockEdges[i]) {
                if (copyV[e->source()] == nullptr) {
                    copyV[e->source()] = bc->newNode();
                    marked.pushBack(e->source());
                }
                if (copyV[e->target()] == nullptr) {
                    copyV[e->target()] = bc->newNode();
                    marked.pushBack(e->target());
                }
 
                (*origE)[bc->newEdge(copyV[e->source()], copyV[e->target()])] = e;
            }
 
            for (node v : marked) {
                copyV[v] = nullptr;
            }
        }
        copyV.init();
 
        int nRuns = max(1, m_nRuns);
        unsigned int nThreads = min(this->maxThreads(), (unsigned int)nRuns);
 
        if (nThreads == 1) {
            seqCall(block, pCost, nRuns, (m_nRuns == 0), delEdges);
        } else {
            parCall(block, pCost, nRuns, nThreads, delEdges);
        }
 
        // clean-up
        for (int i = 0; i < nBlocks; i++) {
            delete block[i].first;
            delete block[i].second;
        }
 
        return Module::ReturnType::Feasible;
    }
 
 
private:
    int m_nRuns; 
 
    void seqCall(const Array<BlockType>& block, const EdgeArray<TCost>* pCost, int nRuns,
            bool randomize, List<edge>& delEdges) {
        const int nBlocks = block.size();
 
        Array<TCost> bestSolution(nBlocks);
        Array<List<edge>*> bestDelEdges(nBlocks);
 
        for (int i = 0; i < nBlocks; ++i) {
            bestDelEdges[i] = nullptr;
            bestSolution[i] = (block[i].first != nullptr) ? std::numeric_limits<TCost>::max() : 0;
        }
 
        for (int run = 0; run < nRuns; ++run) {
            for (int i = 0; i < nBlocks; ++i) {
                if (bestSolution[i] > 1) {
                    const Graph& B = *block[i].first;
                    const EdgeArray<edge>& origEdge = *block[i].second;
 
                    // compute (randomized) st-numbering
                    NodeArray<int> numbering(B, 0);
                    computeSTNumbering(B, numbering, nullptr, nullptr, randomize);
 
                    List<edge>* pCurrentDelEdges = new List<edge>;
                    planarize(B, numbering, *pCurrentDelEdges);
 
                    TCost currentSolution;
                    if (pCost == nullptr) {
                        currentSolution = pCurrentDelEdges->size();
                    } else {
                        currentSolution = 0;
                        for (edge e : *pCurrentDelEdges) {
                            currentSolution += (*pCost)[origEdge[e]];
                        }
                    }
 
                    if (currentSolution < bestSolution[i]) {
                        delete bestDelEdges[i];
                        bestDelEdges[i] = pCurrentDelEdges;
                        bestSolution[i] = currentSolution;
                    } else {
                        delete pCurrentDelEdges;
                    }
                }
            }
        }
 
        // build final solution from block solutions
        for (int i = 0; i < nBlocks; ++i) {
            if (bestDelEdges[i] != nullptr) {
                const EdgeArray<edge>& origEdge = *block[i].second;
                for (edge e : *bestDelEdges[i]) {
                    delEdges.pushBack(origEdge[e]);
                }
                delete bestDelEdges[i];
            }
        }
    }
 
    void parCall(const Array<BlockType>& block, const EdgeArray<TCost>* pCost, int nRuns,
            unsigned int nThreads, List<edge>& delEdges) {
        ThreadMaster master(block, pCost, nRuns - nThreads);
 
        Array<Worker*> worker(nThreads - 1);
        Array<Thread> thread(nThreads - 1);
        for (unsigned int i = 0; i < nThreads - 1; ++i) {
            worker[i] = new Worker(&master);
            thread[i] = Thread(*worker[i]);
        }
 
        doWorkHelper(master);
 
        for (unsigned int i = 0; i < nThreads - 1; ++i) {
            thread[i].join();
            delete worker[i];
        }
 
        master.buildSolution(delEdges);
    }
 
 
    static void planarize(const Graph& G, NodeArray<int>& numbering, List<edge>& delEdges) {
        using PlanarLeafKey = booth_lueker::PlanarLeafKey<whaInfo*>;
 
        NodeArray<SListPure<PlanarLeafKey*>> inLeaves(G);
        NodeArray<SListPure<PlanarLeafKey*>> outLeaves(G);
        Array<node> table(G.numberOfNodes() + 1);
 
        for (node v : G.nodes) {
            for (adjEntry adj : v->adjEntries) {
                edge e = adj->theEdge();
                if (numbering[e->opposite(v)] > numbering[v]) { // sideeffect: ignores selfloops
                    PlanarLeafKey* L = new PlanarLeafKey(e);
                    inLeaves[v].pushFront(L);
                }
            }
            table[numbering[v]] = v;
        }
 
        for (node v : G.nodes) {
            for (PlanarLeafKey* L : inLeaves[v]) {
                outLeaves[L->userStructKey()->opposite(v)].pushFront(L);
            }
        }
 
        SList<PQLeafKey<edge, whaInfo*, bool>*> totalEliminatedKeys;
 
        PlanarSubgraphPQTree T;
        T.Initialize(inLeaves[table[1]]);
        for (int i = 2; i < G.numberOfNodes(); i++) {
            SList<PQLeafKey<edge, whaInfo*, bool>*> eliminatedKeys;
            T.Reduction(outLeaves[table[i]], eliminatedKeys);
            totalEliminatedKeys.conc(eliminatedKeys);
            T.ReplaceRoot(inLeaves[table[i]]);
            T.emptyAllPertinentNodes();
        }
 
        for (PQLeafKey<edge, whaInfo*, bool>* key : totalEliminatedKeys) {
            edge e = key->userStructKey();
            delEdges.pushBack(e);
        }
 
        //cleanup
        for (node v : G.nodes) {
            while (!inLeaves[v].empty()) {
                PlanarLeafKey* L = inLeaves[v].popFrontRet();
                delete L;
            }
        }
 
        T.Cleanup(); // Explicit call for destructor necessary. This allows to call virtual
        // function CleanNode for freeing node information class.
    }
 
    static void doWorkHelper(ThreadMaster& master) {
        const int nBlocks = master.numBlocks();
 
        do {
            for (int i = 0; i < nBlocks; ++i) {
                if (master.considerBlock(i)) {
                    const Graph& B = master.block(i);
 
                    NodeArray<int> numbering(B, 0); // compute (randomized) st-numbering
                    computeSTNumbering(B, numbering, nullptr, nullptr, true);
 
                    List<edge>* pCurrentDelEdges = new List<edge>;
                    planarize(B, numbering, *pCurrentDelEdges);
 
                    pCurrentDelEdges = master.postNewResult(i, pCurrentDelEdges);
                    delete pCurrentDelEdges;
                }
            }
 
        } while (master.getNextRun());
    }
};
 
}