checkqueue.h

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// Copyright (c) 2012-2018 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.

#ifndef BITCOIN_CHECKQUEUE_H
#define BITCOIN_CHECKQUEUE_H

#include <sync.h>

#include <algorithm>
#include <vector>

#include <boost/thread/condition_variable.hpp>
#include <boost/thread/mutex.hpp>

template <typename T>
class CCheckQueueControl;

template <typename T>
class CCheckQueue
{
private:
    boost::mutex mutex;

    boost::condition_variable condWorker;

    boost::condition_variable condMaster;

    std::vector<T> queue;

    int nIdle;

    int nTotal;

    bool fAllOk;

    unsigned int nTodo;

    unsigned int nBatchSize;

    bool Loop(bool fMaster = false)
    {
        boost::condition_variable& cond = fMaster ? condMaster : condWorker;
        std::vector<T> vChecks;
        vChecks.reserve(nBatchSize);
        unsigned int nNow = 0;
        bool fOk = true;
        do {
            {
                boost::unique_lock<boost::mutex> lock(mutex);
                // first do the clean-up of the previous loop run (allowing us to do it in the same critsect)
                if (nNow) {
                    fAllOk &= fOk;
                    nTodo -= nNow;
                    if (nTodo == 0 && !fMaster)
                        // We processed the last element; inform the master it can exit and return the result
                        condMaster.notify_one();
                } else {
                    // first iteration
                    nTotal++;
                }
                // logically, the do loop starts here
                while (queue.empty()) {
                    if (fMaster && nTodo == 0) {
                        nTotal--;
                        bool fRet = fAllOk;
                        // reset the status for new work later
                        fAllOk = true;
                        // return the current status
                        return fRet;
                    }
                    nIdle++;
                    cond.wait(lock); // wait
                    nIdle--;
                }
                // Decide how many work units to process now.
                // * Do not try to do everything at once, but aim for increasingly smaller batches so
                //   all workers finish approximately simultaneously.
                // * Try to account for idle jobs which will instantly start helping.
                // * Don't do batches smaller than 1 (duh), or larger than nBatchSize.
                nNow = std::max(1U, std::min(nBatchSize, (unsigned int)queue.size() / (nTotal + nIdle + 1)));
                vChecks.resize(nNow);
                for (unsigned int i = 0; i < nNow; i++) {
                    // We want the lock on the mutex to be as short as possible, so swap jobs from the global
                    // queue to the local batch vector instead of copying.
                    vChecks[i].swap(queue.back());
                    queue.pop_back();
                }
                // Check whether we need to do work at all
                fOk = fAllOk;
            }
            // execute work
            for (T& check : vChecks)
                if (fOk)
                    fOk = check();
            vChecks.clear();
        } while (true);
    }

public:
    boost::mutex ControlMutex;

    explicit CCheckQueue(unsigned int nBatchSizeIn) : nIdle(0), nTotal(0), fAllOk(true), nTodo(0), nBatchSize(nBatchSizeIn) {}

    void Thread()
    {
        Loop();
    }

    bool Wait()
    {
        return Loop(true);
    }

    void Add(std::vector<T>& vChecks)
    {
        boost::unique_lock<boost::mutex> lock(mutex);
        for (T& check : vChecks) {
            queue.push_back(T());
            check.swap(queue.back());
        }
        nTodo += vChecks.size();
        if (vChecks.size() == 1)
            condWorker.notify_one();
        else if (vChecks.size() > 1)
            condWorker.notify_all();
    }

    ~CCheckQueue()
    {
    }

};

template <typename T>
class CCheckQueueControl
{
private:
    CCheckQueue<T> * const pqueue;
    bool fDone;

public:
    CCheckQueueControl() = delete;
    CCheckQueueControl(const CCheckQueueControl&) = delete;
    CCheckQueueControl& operator=(const CCheckQueueControl&) = delete;
    explicit CCheckQueueControl(CCheckQueue<T> * const pqueueIn) : pqueue(pqueueIn), fDone(false)
    {
        // passed queue is supposed to be unused, or nullptr
        if (pqueue != nullptr) {
            ENTER_CRITICAL_SECTION(pqueue->ControlMutex);
        }
    }

    bool Wait()
    {
        if (pqueue == nullptr)
            return true;
        bool fRet = pqueue->Wait();
        fDone = true;
        return fRet;
    }

    void Add(std::vector<T>& vChecks)
    {
        if (pqueue != nullptr)
            pqueue->Add(vChecks);
    }

    ~CCheckQueueControl()
    {
        if (!fDone)
            Wait();
        if (pqueue != nullptr) {
            LEAVE_CRITICAL_SECTION(pqueue->ControlMutex);
        }
    }
};

#endif // BITCOIN_CHECKQUEUE_H