scheduler.h

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// 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.

#ifndef BITCOIN_SCHEDULER_H
#define BITCOIN_SCHEDULER_H

#include <attributes.h>
#include <sync.h>
#include <threadsafety.h>
#include <util/task_runner.h>

#include <chrono>
#include <condition_variable>
#include <cstddef>
#include <functional>
#include <list>
#include <map>
#include <thread>
#include <utility>

class CScheduler
{
public:
    CScheduler();
    ~CScheduler();

    std::thread m_service_thread;

    typedef std::function<void()> Function;

    void schedule(Function f, std::chrono::steady_clock::time_point t) EXCLUSIVE_LOCKS_REQUIRED(!newTaskMutex);

    void scheduleFromNow(Function f, std::chrono::milliseconds delta) EXCLUSIVE_LOCKS_REQUIRED(!newTaskMutex)
    {
        schedule(std::move(f), std::chrono::steady_clock::now() + delta);
    }

    void scheduleEvery(Function f, std::chrono::milliseconds delta) EXCLUSIVE_LOCKS_REQUIRED(!newTaskMutex);

    void MockForward(std::chrono::seconds delta_seconds) EXCLUSIVE_LOCKS_REQUIRED(!newTaskMutex);

    void serviceQueue() EXCLUSIVE_LOCKS_REQUIRED(!newTaskMutex);

    void stop() EXCLUSIVE_LOCKS_REQUIRED(!newTaskMutex)
    {
        WITH_LOCK(newTaskMutex, stopRequested = true);
        newTaskScheduled.notify_all();
        if (m_service_thread.joinable()) m_service_thread.join();
    }
    void StopWhenDrained() EXCLUSIVE_LOCKS_REQUIRED(!newTaskMutex)
    {
        WITH_LOCK(newTaskMutex, stopWhenEmpty = true);
        newTaskScheduled.notify_all();
        if (m_service_thread.joinable()) m_service_thread.join();
    }

    size_t getQueueInfo(std::chrono::steady_clock::time_point& first,
                        std::chrono::steady_clock::time_point& last) const
        EXCLUSIVE_LOCKS_REQUIRED(!newTaskMutex);

    bool AreThreadsServicingQueue() const EXCLUSIVE_LOCKS_REQUIRED(!newTaskMutex);

private:
    mutable Mutex newTaskMutex;
    std::condition_variable newTaskScheduled;
    std::multimap<std::chrono::steady_clock::time_point, Function> taskQueue GUARDED_BY(newTaskMutex);
    int nThreadsServicingQueue GUARDED_BY(newTaskMutex){0};
    bool stopRequested GUARDED_BY(newTaskMutex){false};
    bool stopWhenEmpty GUARDED_BY(newTaskMutex){false};
    bool shouldStop() const EXCLUSIVE_LOCKS_REQUIRED(newTaskMutex) { return stopRequested || (stopWhenEmpty && taskQueue.empty()); }
};

class SerialTaskRunner : public util::TaskRunnerInterface
{
private:
    CScheduler& m_scheduler;

    Mutex m_callbacks_mutex;

    // We are not allowed to assume the scheduler only runs in one thread,
    // but must ensure all callbacks happen in-order, so we end up creating
    // our own queue here :(
    std::list<std::function<void()>> m_callbacks_pending GUARDED_BY(m_callbacks_mutex);
    bool m_are_callbacks_running GUARDED_BY(m_callbacks_mutex) = false;

    void MaybeScheduleProcessQueue() EXCLUSIVE_LOCKS_REQUIRED(!m_callbacks_mutex);
    void ProcessQueue() EXCLUSIVE_LOCKS_REQUIRED(!m_callbacks_mutex);

public:
    explicit SerialTaskRunner(CScheduler& scheduler LIFETIMEBOUND) : m_scheduler{scheduler} {}

    void insert(std::function<void()> func) override EXCLUSIVE_LOCKS_REQUIRED(!m_callbacks_mutex);

    void flush() override EXCLUSIVE_LOCKS_REQUIRED(!m_callbacks_mutex);

    size_t size() override EXCLUSIVE_LOCKS_REQUIRED(!m_callbacks_mutex);
};

#endif // BITCOIN_SCHEDULER_H