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