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// Copyright (c) 2015-2020 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
//
// NOTE:
// boost::thread should be ported to std::thread
// when we support C++11.
//
#include <condition_variable>
#include <functional>
#include <list>
#include <map>
#include <sync.h>
//
// Simple class for background tasks that should be run
// periodically or once "after a while"
//
// Usage:
//
// CScheduler* s = new CScheduler();
// s->scheduleFromNow(doSomething, std::chrono::milliseconds{11}); // Assuming a: void doSomething() { }
// s->scheduleFromNow([=] { this->func(argument); }, std::chrono::milliseconds{3});
// boost::thread* t = new boost::thread(std::bind(CScheduler::serviceQueue, s));
//
// ... then at program shutdown, make sure to call stop() to clean up the thread(s) running serviceQueue:
// s->stop();
// t->join();
// delete t;
// delete s; // Must be done after thread is interrupted/joined.
//
class CScheduler
{
public:
CScheduler();
~CScheduler();
typedef std::function<void()> Function;
// Call func at/after time t
void schedule(Function f, std::chrono::system_clock::time_point t);
/** Call f once after the delta has passed */
void scheduleFromNow(Function f, std::chrono::milliseconds delta)
{
schedule(std::move(f), std::chrono::system_clock::now() + delta);
}
/**
* Repeat f until the scheduler is stopped. First run is after delta has passed once.
*
* The timing is not exact: Every time f is finished, it is rescheduled to run again after delta. If you need more
* accurate scheduling, don't use this method.
*/
void scheduleEvery(Function f, std::chrono::milliseconds delta);
/**
* Mock the scheduler to fast forward in time.
* Iterates through items on taskQueue and reschedules them
* to be delta_seconds sooner.
*/
void MockForward(std::chrono::seconds delta_seconds);
// To keep things as simple as possible, there is no unschedule.
// Services the queue 'forever'. Should be run in a thread,
// and interrupted using boost::interrupt_thread
void serviceQueue();
// Tell any threads running serviceQueue to stop as soon as they're
// done servicing whatever task they're currently servicing (drain=false)
// or when there is no work left to be done (drain=true)
void stop(bool drain=false);
// Returns number of tasks waiting to be serviced,
// and first and last task times
size_t getQueueInfo(std::chrono::system_clock::time_point &first,
std::chrono::system_clock::time_point &last) const;
// Returns true if there are threads actively running in serviceQueue()
bool AreThreadsServicingQueue() const;
private:
mutable Mutex newTaskMutex;
std::condition_variable newTaskScheduled;
std::multimap<std::chrono::system_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 used by CScheduler clients which may schedule multiple jobs
* which are required to be run serially. Jobs may not be run on the
* same thread, but no two jobs will be executed
* at the same time and memory will be release-acquire consistent
* (the scheduler will internally do an acquire before invoking a callback
* as well as a release at the end). In practice this means that a callback
* B() will be able to observe all of the effects of callback A() which executed
* before it.
*/
class SingleThreadedSchedulerClient {
private:
CScheduler *m_pscheduler;
RecursiveMutex m_cs_callbacks_pending;
std::list<std::function<void ()>> m_callbacks_pending GUARDED_BY(m_cs_callbacks_pending);
bool m_are_callbacks_running GUARDED_BY(m_cs_callbacks_pending) = false;
void MaybeScheduleProcessQueue();
void ProcessQueue();
public:
explicit SingleThreadedSchedulerClient(CScheduler *pschedulerIn) : m_pscheduler(pschedulerIn) {}
/**
* Add a callback to be executed. Callbacks are executed serially
* and memory is release-acquire consistent between callback executions.
* Practically, this means that callbacks can behave as if they are executed
* in order by a single thread.
*/
void AddToProcessQueue(std::function<void ()> func);
// Processes all remaining queue members on the calling thread, blocking until queue is empty
// Must be called after the CScheduler has no remaining processing threads!
void EmptyQueue();
size_t CallbacksPending();
};
#endif
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