thehub/hub/server/scheduler.cpp

/*
 * This file is part of the Flowee project
 * Copyright (C) 2015 The Bitcoin Core developers
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * 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
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "scheduler.h"

#include <cassert>
#include <boost/thread/reverse_lock.hpp>
#include <utility>

CScheduler::CScheduler() : nThreadsServicingQueue(0), stopRequested(false), stopWhenEmpty(false)
{
}

CScheduler::~CScheduler()
{
    assert(nThreadsServicingQueue == 0);
}

void CScheduler::serviceQueue()
{
    boost::unique_lock<boost::mutex> lock(newTaskMutex);
    ++nThreadsServicingQueue;

    // newTaskMutex is locked throughout this loop EXCEPT
    // when the thread is waiting or when the user's function
    // is called.
    while (!shouldStop()) {
        try {
            while (!shouldStop() && taskQueue.empty()) {
                // Wait until there is something to do.
                newTaskScheduled.wait(lock);
            }

            // Wait until either there is a new task, or until
            // the time of the first item on the queue:

            // Some boost versions have a conflicting overload of wait_until that returns void.
            // Explicitly use a template here to avoid hitting that overload.
            while (!shouldStop() && !taskQueue.empty() &&
                   newTaskScheduled.wait_until<>(lock, taskQueue.begin()->first) != boost::cv_status::timeout) {
                // Keep waiting until timeout
            }
            // If there are multiple threads, the queue can empty while we're waiting (another
            // thread may service the task we were waiting on).
            if (shouldStop() || taskQueue.empty())
                continue;

            Function f = taskQueue.begin()->second;
            taskQueue.erase(taskQueue.begin());

            {
                // Unlock before calling f, so it can reschedule itself or another task
                // without deadlocking:
                boost::reverse_lock<boost::unique_lock<boost::mutex> > rlock(lock);
                f();
            }
        } catch (...) {
            --nThreadsServicingQueue;
            throw;
        }
    }
    --nThreadsServicingQueue;
}

void CScheduler::stop(bool drain)
{
    {
        boost::unique_lock<boost::mutex> lock(newTaskMutex);
        if (drain)
            stopWhenEmpty = true;
        else
            stopRequested = true;
    }
    newTaskScheduled.notify_all();
}

void CScheduler::schedule(CScheduler::Function f, boost::chrono::system_clock::time_point t)
{
    {
        boost::unique_lock<boost::mutex> lock(newTaskMutex);
        taskQueue.insert(std::make_pair(t, f));
    }
    newTaskScheduled.notify_one();
}

void CScheduler::scheduleFromNow(CScheduler::Function f, int64_t deltaSeconds)
{
    schedule(f, boost::chrono::system_clock::now() + boost::chrono::seconds(deltaSeconds));
}

static void Repeat(CScheduler* s, CScheduler::Function f, int64_t deltaSeconds)
{
    f();
    s->scheduleFromNow(std::bind(&Repeat, s, f, deltaSeconds), deltaSeconds);
}

void CScheduler::scheduleEvery(CScheduler::Function f, int64_t deltaSeconds)
{
    scheduleFromNow(std::bind(&Repeat, this, f, deltaSeconds), deltaSeconds);
}

size_t CScheduler::getQueueInfo(boost::chrono::system_clock::time_point &first,
                             boost::chrono::system_clock::time_point &last) const
{
    boost::unique_lock<boost::mutex> lock(newTaskMutex);
    size_t result = taskQueue.size();
    if (!taskQueue.empty()) {
        first = taskQueue.begin()->first;
        last = taskQueue.rbegin()->first;
    }
    return result;
}