// Copyright (c) 2015-2022 The Bitcoin Core developers

// Distributed under the MIT software license, see the accompanying

// file COPYING or http://www.opensource.org/licenses/mit-license.php.

#include <scheduler.h>

#include <sync.h>

#include <util/time.h>

#include <cassert>

#include <functional>

#include <utility>

CScheduler::CScheduler() = default;

CScheduler::~CScheduler()

{

    assert(nThreadsServicingQueue == 0);

    if (stopWhenEmpty) assert(taskQueue.empty());

}

void CScheduler::serviceQueue()

{

    WAIT_LOCK(newTaskMutex, lock);

    ++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:

            while (!shouldStop() && !taskQueue.empty()) {

                std::chrono::steady_clock::time_point timeToWaitFor = taskQueue.begin()->first;

                if (newTaskScheduled.wait_until(lock, timeToWaitFor) == std::cv_status::timeout) {

                    break; // Exit loop after timeout, it means we reached the time of the event

                }

            }

            // 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:

                REVERSE_LOCK(lock);

                f();

            }

        } catch (...) {

            --nThreadsServicingQueue;

            throw;

        }

    }

    --nThreadsServicingQueue;

    newTaskScheduled.notify_one();

}

void CScheduler::schedule(CScheduler::Function f, std::chrono::steady_clock::time_point t)

{

    {

        LOCK(newTaskMutex);

        taskQueue.insert(std::make_pair(t, f));

    }

    newTaskScheduled.notify_one();

}

void CScheduler::MockForward(std::chrono::seconds delta_seconds)

{

    assert(delta_seconds > 0s && delta_seconds <= 1h);

    {

        LOCK(newTaskMutex);

        // use temp_queue to maintain updated schedule

        std::multimap<std::chrono::steady_clock::time_point, Function> temp_queue;

        for (const auto& element : taskQueue) {

            temp_queue.emplace_hint(temp_queue.cend(), element.first - delta_seconds, element.second);

        }

        // point taskQueue to temp_queue

        taskQueue = std::move(temp_queue);

    }

    // notify that the taskQueue needs to be processed

    newTaskScheduled.notify_one();

}

static void Repeat(CScheduler& s, CScheduler::Function f, std::chrono::milliseconds delta)

{

    f();

    s.scheduleFromNow([=, &s] { Repeat(s, f, delta); }, delta);

}

void CScheduler::scheduleEvery(CScheduler::Function f, std::chrono::milliseconds delta)

{

    scheduleFromNow([this, f, delta] { Repeat(*this, f, delta); }, delta);

}

size_t CScheduler::getQueueInfo(std::chrono::steady_clock::time_point& first,

                                std::chrono::steady_clock::time_point& last) const

{

    LOCK(newTaskMutex);

    size_t result = taskQueue.size();

    if (!taskQueue.empty()) {

        first = taskQueue.begin()->first;

        last = taskQueue.rbegin()->first;

    }

    return result;

}

bool CScheduler::AreThreadsServicingQueue() const

{

    LOCK(newTaskMutex);

    return nThreadsServicingQueue;

}

void SerialTaskRunner::MaybeScheduleProcessQueue()

{

    {

        LOCK(m_callbacks_mutex);

        // Try to avoid scheduling too many copies here, but if we

        // accidentally have two ProcessQueue's scheduled at once its

        // not a big deal.

        if (m_are_callbacks_running) return;

        if (m_callbacks_pending.empty()) return;

    }

    m_scheduler.schedule([this] { this->ProcessQueue(); }, std::chrono::steady_clock::now());

}

void SerialTaskRunner::ProcessQueue()

{

    std::function<void()> callback;

    {

        LOCK(m_callbacks_mutex);

        if (m_are_callbacks_running) return;

        if (m_callbacks_pending.empty()) return;

        m_are_callbacks_running = true;

        callback = std::move(m_callbacks_pending.front());

        m_callbacks_pending.pop_front();

    }

    // RAII the setting of fCallbacksRunning and calling MaybeScheduleProcessQueue

    // to ensure both happen safely even if callback() throws.

    struct RAIICallbacksRunning {

        SerialTaskRunner* instance;

        explicit RAIICallbacksRunning(SerialTaskRunner* _instance) : instance(_instance) {}

        ~RAIICallbacksRunning()

        {

            {

                LOCK(instance->m_callbacks_mutex);

                instance->m_are_callbacks_running = false;

            }

            instance->MaybeScheduleProcessQueue();

        }

    } raiicallbacksrunning(this);

    callback();

}

void SerialTaskRunner::insert(std::function<void()> func)

{

    {

        LOCK(m_callbacks_mutex);

        m_callbacks_pending.emplace_back(std::move(func));

    }

    MaybeScheduleProcessQueue();

}

void SerialTaskRunner::flush()

{

    assert(!m_scheduler.AreThreadsServicingQueue());

    bool should_continue = true;

    while (should_continue) {

        ProcessQueue();

        LOCK(m_callbacks_mutex);

        should_continue = !m_callbacks_pending.empty();

    }

}

size_t SerialTaskRunner::size()

{

    LOCK(m_callbacks_mutex);

    return m_callbacks_pending.size();

}