比特币源码分析:任务调度器的使用

任务调度器

Bitcoin 进程启动后，有一个专门的线程做任务调度， 这些任务根据指定的时刻，执行对应的函数:

bool AppInitMain() { ....... // Start the lightweight task scheduler thread CScheduler::Function serviceLoop = boost::bind(&CScheduler::serviceQueue, &scheduler); threadGroup.create_thread(boost::bind(&TraceThread, "scheduler", serviceLoop)); ....... }

调度器类主要是实现了一个生产者消费者的任务队列，只是这个任务队列是用 std::multimap 实现的，map 的key表达某一时刻，map的值表达：那一时刻要执行的函数，内部使用条件变量和锁来保护multimap ，还有几个bool 条件:

class CScheduler { public: CScheduler(); ~CScheduler(); typedef std::function Function; void schedule(Function f, boost::chrono::system_clock::time_point t=boost::chrono::system_clock::now()); void scheduleFromNow(Function f, int64_t deltaMilliSeconds); void scheduleEvery(Function f, int64_t deltaMilliSeconds); void serviceQueue(); void stop(bool drain=false); size_t getQueueInfo(boost::chrono::system_clock::time_point &first, boost::chrono::system_clock::time_point &last) const; bool AreThreadsServicingQueue() const; private: std::multimap taskQueue; boost::condition_variable newTaskScheduled; mutable boost::mutex newTaskMutex; int nThreadsServicingQueue; bool stopRequested; bool stopWhenEmpty; bool shouldStop() const { return stopRequested || (stopWhenEmpty && taskQueue.empty()); } };

CScheduler的client 通过调用schedule 往内部multimap添加一个条目; scheduleFromNow 和scheduleEvery 内部都是调用schedule 方法实现; 这三个方法属于生产者要生产任务的方法， 任务的消费者调用serviceQueue等待取走任务， 然后执行。

目前整个程序有一个全局的CScheduler实例:

static CScheduler scheduler; 这个实例对应只有一个消费者线程， 即唯一的后台调度器线程。

class SingleThreadedSchedulerClient 主要用途是，借助CScheduler类型，保障被添加到内部链表的任务，被串行执行:

class SingleThreadedSchedulerClient { private: CScheduler *m_pscheduler; CCriticalSection m_cs_callbacks_pending; std::list m_callbacks_pending; bool m_are_callbacks_running = false; void MaybeScheduleProcessQueue(); void ProcessQueue(); public: explicit SingleThreadedSchedulerClient(CScheduler *pschedulerIn) : m_pscheduler(pschedulerIn) {} void AddToProcessQueue(std::function func); void EmptyQueue(); size_t CallbacksPending(); };

使用例子

基本的使用例子:

#include #include  #include  #include  #include static void doN(){ std::cout << "output now\n"; } static void doE(){ for(int i = 0; i < 10; i++){ std::cout << "i = " << i << '\n'; } std::cout << '\n'; } BOOST_AUTO_TEST_SUITE(sche_tests) BOOST_AUTO_TEST_CASE(sche) { CScheduler s; s.scheduleFromNow(doN, 1000); s.scheduleEvery(doE, 1000); boost::thread t(boost::bind(&CScheduler::serviceQueue, &s)); boost::this_thread::sleep_for(boost::chrono::seconds{5}); t.interrupt(); t.join(); } BOOST_AUTO_TEST_CASE(singlethread) { CScheduler s; SingleThreadedSchedulerClient sc (&s); for(int i = 1; i <11; i++){ auto f = [=]{ std::cout << "thread " << boost::this_thread::get_id() << " print arg: " << i << '\n'; }; sc.AddToProcessQueue(f); } boost::thread t(boost::bind(&CScheduler::serviceQueue, &s)); boost::this_thread::sleep_for(boost::chrono::seconds{1}); t.interrupt(); t.join(); } BOOST_AUTO_TEST_SUITE_END()

进程启动后， 全局对象连接管理器connman初始化后， connman 的Start 方法最后，通过scheduler 线程安排了一个定时任务: 每隔15分钟， 把connman 对象内部成员，banmap_t 类型的 setBanned, CAddrMan 类型的addrman 序列化到本地文件banlist.dat 和 peers.dat。

//init.cpp if (!connman.Start(scheduler, connOptions)) { return false; } //net.cpp bool CConnman::Start(CScheduler& scheduler, const Options& connOptions) { ............... scheduler.scheduleEvery(std::bind(&CConnman::DumpData, this), DUMP_ADDRESSES_INTERVAL * 1000); }

如果钱包功能编译使能, 会让scheduler 线程安排每隔500毫秒刷新钱包状态。

//init.cpp #ifdef ENABLE_WALLET StartWallets(scheduler); #endif //wallet/init.cpp void StartWallets(CScheduler& scheduler) { for (CWalletRef pwallet : vpwallets) { pwallet->postInitProcess(scheduler); } } //wallet/wallet.cpp void CWallet::postInitProcess(CScheduler& scheduler) { ReacceptWalletTransactions(); if (!CWallet::fFlushScheduled.exchange(true)) { scheduler.scheduleEvery(MaybeCompactWalletDB, 500); } }

PeerLogicValidation 对象的构造函数内部, scheduler 线程安排每45秒执行CheckForStaleTipAndEvictPeer函数主要做两件事:

1. 关掉多余的外出tcp 连接

2. 根据当前时间，检查当前节点的blockchain 的tip 是否有可能过时了，建立额外的连接同步跟上

PeerLogicValidation::PeerLogicValidation(CConnman* connmanIn, CScheduler &scheduler) : connman(connmanIn), m_stale_tip_check_time(0) { // Initialize global variables that cannot be constructed at startup. recentRejects.reset(new CRollingBloomFilter(120000, 0.000001)); const Consensus::Params& consensusParams = Params().GetConsensus(); // Stale tip checking and peer eviction are on two different timers, but we // don't want them to get out of sync due to drift in the scheduler, so we // combine them in one function and schedule at the quicker (peer-eviction) // timer. static_assert(EXTRA_PEER_CHECK_INTERVAL < STALE_CHECK_INTERVAL, "peer eviction timer should be less than stale tip check timer"); scheduler.scheduleEvery(std::bind(&PeerLogicValidation::CheckForStaleTipAndEvictPeers, this, consensusParams), EXTRA_PEER_CHECK_INTERVAL * 1000); } void PeerLogicValidation::CheckForStaleTipAndEvictPeers(const Consensus::Params &consensusParams) { if (connman == nullptr) return; int64_t time_in_seconds = GetTime(); EvictExtraOutboundPeers(time_in_seconds); if (time_in_seconds > m_stale_tip_check_time) { LOCK(cs_main); // Check whether our tip is stale, and if so, allow using an extra // outbound peer if (TipMayBeStale(consensusParams)) { LogPrintf("Potential stale tip detected, will try using extra outbound peer (last tip update: %d seconds ago)\n", time_in_seconds - g_last_tip_update); connman->SetTryNewOutboundPeer(true); } else if (connman->GetTryNewOutboundPeer()) { connman->SetTryNewOutboundPeer(false); } m_stale_tip_check_time = time_in_seconds + STALE_CHECK_INTERVAL; } }

以上就是bitoin 里面CScheduler类的主要使用场景。