src/scheduler.h

   1 // Copyright (c) 2015-2017 The Bitcoin Core developers
   2 // Distributed under the MIT software license, see the accompanying
   3 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
   4
   5 #ifndef BITCOIN_SCHEDULER_H
   6 #define BITCOIN_SCHEDULER_H
   7
   8 //
   9 // NOTE:
  10 // boost::thread / boost::chrono should be ported to std::thread / std::chrono
  11 // when we support C++11.
  12 //
  13 #include <boost/chrono/chrono.hpp>
  14 #include <boost/thread.hpp>
  15 #include <map>
  16
  17 #include <sync.h>
  18
  19 //
  20 // Simple class for background tasks that should be run
  21 // periodically or once "after a while"
  22 //
  23 // Usage:
  24 //
  25 // CScheduler* s = new CScheduler();
  26 // s->scheduleFromNow(doSomething, 11); // Assuming a: void doSomething() { }
  27 // s->scheduleFromNow(std::bind(Class::func, this, argument), 3);
  28 // boost::thread* t = new boost::thread(boost::bind(CScheduler::serviceQueue, s));
  29 //
  30 // ... then at program shutdown, clean up the thread running serviceQueue:
  31 // t->interrupt();
  32 // t->join();
  33 // delete t;
  34 // delete s; // Must be done after thread is interrupted/joined.
  35 //
  36
  37 class CScheduler
  38 {
  39 public:
  40     CScheduler();
  41     ~CScheduler();
  42
  43     typedef std::function<void(void)> Function;
  44
  45     // Call func at/after time t
  46     void schedule(Function f, boost::chrono::system_clock::time_point t=boost::chrono::system_clock::now());
  47
  48     // Convenience method: call f once deltaSeconds from now
  49     void scheduleFromNow(Function f, int64_t deltaMilliSeconds);
  50
  51     // Another convenience method: call f approximately
  52     // every deltaSeconds forever, starting deltaSeconds from now.
  53     // To be more precise: every time f is finished, it
  54     // is rescheduled to run deltaSeconds later. If you
  55     // need more accurate scheduling, don't use this method.
  56     void scheduleEvery(Function f, int64_t deltaMilliSeconds);
  57
  58     // To keep things as simple as possible, there is no unschedule.
  59
  60     // Services the queue 'forever'. Should be run in a thread,
  61     // and interrupted using boost::interrupt_thread
  62     void serviceQueue();
  63
  64     // Tell any threads running serviceQueue to stop as soon as they're
  65     // done servicing whatever task they're currently servicing (drain=false)
  66     // or when there is no work left to be done (drain=true)
  67     void stop(bool drain=false);
  68
  69     // Returns number of tasks waiting to be serviced,
  70     // and first and last task times
  71     size_t getQueueInfo(boost::chrono::system_clock::time_point &first,
  72                         boost::chrono::system_clock::time_point &last) const;
  73
  74     // Returns true if there are threads actively running in serviceQueue()
  75     bool AreThreadsServicingQueue() const;
  76
  77 private:
  78     std::multimap<boost::chrono::system_clock::time_point, Function> taskQueue;
  79     boost::condition_variable newTaskScheduled;
  80     mutable boost::mutex newTaskMutex;
  81     int nThreadsServicingQueue;
  82     bool stopRequested;
  83     bool stopWhenEmpty;
  84     bool shouldStop() const { return stopRequested || (stopWhenEmpty && taskQueue.empty()); }
  85 };
  86
  87 /**
  88  * Class used by CScheduler clients which may schedule multiple jobs
  89  * which are required to be run serially. Does not require such jobs
  90  * to be executed on the same thread, but no two jobs will be executed
  91  * at the same time.
  92  */
  93 class SingleThreadedSchedulerClient {
  94 private:
  95     CScheduler *m_pscheduler;
  96
  97     CCriticalSection m_cs_callbacks_pending;
  98     std::list<std::function<void (void)>> m_callbacks_pending;
  99     bool m_are_callbacks_running = false;
 100
 101     void MaybeScheduleProcessQueue();
 102     void ProcessQueue();
 103
 104 public:
 105     explicit SingleThreadedSchedulerClient(CScheduler *pschedulerIn) : m_pscheduler(pschedulerIn) {}
 106     void AddToProcessQueue(std::function<void (void)> func);
 107
 108     // Processes all remaining queue members on the calling thread, blocking until queue is empty
 109     // Must be called after the CScheduler has no remaining processing threads!
 110     void EmptyQueue();
 111
 112     size_t CallbacksPending();
 113 };
 114
 115 #endif