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比特币源码分析-boost::signal 的使用

bitcoin 代码中大量使用 boost::signal, boost::signal 实现了信号与槽的事件通知机制,或者说是一种消息的发布与订阅机制, signal 类型是一个可调用类型,slot 就是callback 对象,或者说事件的订阅者,signal 实例是一个可调用对象,调用signal 对象,就相当于发布了相应的事件, signal 的connectdisconnect 方法分别相当于对事件的订阅,取消。

#include <boost/signals2.hpp> #include void print_args(float x, float y) { std::cout << "The arguments are " << x << " and " << y << std::endl; } void print_sum(float x, float y) { std::cout << "The sum is " << x + y << std::endl; } void print_product(float x, float y) { std::cout << "The product is " << x * y << std::endl; } void print_difference(float x, float y) { std::cout << "The difference is " << x - y << std::endl; } void print_quotient(float x, float y) { std::cout << "The quotient is " << x / y << std::endl; } int main() { boost::signals2::signal<void(float, float)> sig; sig.connect(print_args); sig.connect(print_sum); sig.connect(print_product); sig.connect(print_difference); sig.connect(print_quotient); sig(5., 3.); return 0;

上面这个例子, 有五个函数订阅sig 事件,sig(5. , 3.) 的调用触发事件,参数5,3,相当于事件携带的消息paylaod, 传给了五个事件订阅者。

bitcoin 中定义了类型CMainSignals 来统一管理各个功能模块的事件通知,CMainSignal 是一个资源管理类型, 主要工作代理给由unique_ptr 管理内存的成员 m_internals , 它的类型是MainSignalsInstance,内部定义十个boost signal 变量, 分别表达十种要通知的事件。

class CMainSignals { private: std::unique_ptr m_internals; friend void ::RegisterValidationInterface(CValidationInterface*); friend void ::UnregisterValidationInterface(CValidationInterface*); friend void ::UnregisterAllValidationInterfaces(); friend void ::CallFunctionInValidationInterfaceQueue(std::function func); void MempoolEntryRemoved(CTransactionRef tx, MemPoolRemovalReason reason);public: /** Register a CScheduler to give callbacks which should run in the background (may only be called once) */ void RegisterBackgroundSignalScheduler(CScheduler& scheduler); /** Unregister a CScheduler to give callbacks which should run in the background - these callbacks will now be dropped! */ void UnregisterBackgroundSignalScheduler(); /** Call any remaining callbacks on the calling thread */ void FlushBackgroundCallbacks(); size_t CallbacksPending(); /** Register with mempool to call TransactionRemovedFromMempool callbacks */ void RegisterWithMempoolSignals(CTxMemPool& pool); /** Unregister with mempool */ void UnregisterWithMempoolSignals(CTxMemPool& pool); void UpdatedBlockTip(const CBlockIndex *, const CBlockIndex *, bool fInitialDownload); void TransactionAddedToMempool(const CTransactionRef &); void BlockConnected(const std::shared_ptr &, const CBlockIndex *pindex, const std::shared_ptr> &); void BlockDisconnected(const std::shared_ptr &); void SetBestChain(const CBlockLocator &); void Inventory(const uint256 &); void Broadcast(int64_t nBestBlockTime, CConnman* connman); void BlockChecked(const CBlock&, const CValidationState&); void NewPoWValidBlock(const CBlockIndex *, const std::shared_ptr&); }; struct MainSignalsInstance { boost::signals2::signal UpdatedBlockTip; boost::signals2::signal TransactionAddedToMempool; boost::signals2::signal &, const CBlockIndex *pindex, const std::vector&)> BlockConnected; boost::signals2::signal &)> BlockDisconnected; boost::signals2::signal TransactionRemovedFromMempool; boost::signals2::signal SetBestChain; boost::signals2::signal Inventory; boost::signals2::signal Broadcast; boost::signals2::signal BlockChecked; boost::signals2::signal&)> NewPoWValidBlock; // 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 :( SingleThreadedSchedulerClient m_schedulerClient; explicit MainSignalsInstance(CScheduler *pscheduler) : m_schedulerClient(pscheduler) {} };

类型CValidationInterface 主要是统一表示某些对MainSignalsInstance 中定义的十个事件感兴趣的对象, 即这些事件的订阅者, 所有对这些事件感兴趣代码继承CValidationInterface类型,提供自己版本的这些虚成员函数的实现,覆盖baseCValidationInterface 中对应的空方法, 表达对相应的事件感兴趣, 不感兴趣的事件的回调方法继续是那些继承自base class 的空方法。

class CValidationInterface { protected: virtual void UpdatedBlockTip(const CBlockIndex *pindexNew, const CBlockIndex *pindexFork, bool fInitialDownload) {} virtual void TransactionAddedToMempool(const CTransactionRef &ptxn) {} virtual void TransactionRemovedFromMempool(const CTransactionRef &ptx) {} virtual void BlockConnected(const std::shared_ptr &block, const CBlockIndex *pindex, const std::vector &txnConflicted) {} virtual void BlockDisconnected(const std::shared_ptr &block) {} virtual void SetBestChain(const CBlockLocator &locator) {} virtual void Inventory(const uint256 &hash) {} virtual void ResendWalletTransactions(int64_t nBestBlockTime, CConnman* connman) {} virtual void BlockChecked(const CBlock&, const CValidationState&) {} virtual void NewPoWValidBlock(const CBlockIndex *pindex, const std::shared_ptr& block) {}; friend void ::RegisterValidationInterface(CValidationInterface*); friend void ::UnregisterValidationInterface(CValidationInterface*); friend void ::UnregisterAllValidationInterfaces(); };

CValidationInterface 有四个子类, CWallet , CZMQNotificationInterface, submitblock_StateCatcher, PeerLogicValidation 分别对应四个对MainSignalsInstance 中的事件感兴趣的订阅者。

 class CWallet final : public CCryptoKeyStore, public CValidationInterface { ............... void TransactionAddedToMempool(const CTransactionRef& tx) override; void BlockConnected(const std::shared_ptr& pblock, const CBlockIndex *pindex, const std::vector& vtxConflicted) override; void BlockDisconnected(const std::shared_ptr& pblock) override; void TransactionRemovedFromMempool(const CTransactionRef &ptx) override; void ResendWalletTransactions(int64_t nBestBlockTime, CConnman* connman) override; void SetBestChain(const CBlockLocator& loc) override; void Inventory(const uint256 &hash) override { { LOCK(cs_wallet); std::map<uint256, int>::iterator mi = mapRequestCount.find(hash); if (mi != mapRequestCount.end()) (*mi).second++; } } ............... }; class CZMQNotificationInterface final : public CValidationInterface { ................ // CValidationInterface void TransactionAddedToMempool(const CTransactionRef& tx) override; void BlockConnected(const std::shared_ptr& pblock, const CBlockIndex* pindexConnected, const std::vector& vtxConflicted) override; void BlockDisconnected(const std::shared_ptr& pblock) override; void UpdatedBlockTip(const CBlockIndex *pindexNew, const CBlockIndex *pindexFork, bool fInitialDownload) override; ................. }; class submitblock_StateCatcher : public CValidationInterface { public: uint256 hash; bool found; CValidationState state; explicit submitblock_StateCatcher(const uint256 &hashIn) : hash(hashIn), found(false), state() {} protected: void BlockChecked(const CBlock& block, const CValidationState& stateIn) override { if (block.GetHash() != hash) return; found = true; state = stateIn; } }; class PeerLogicValidation : public CValidationInterface, public NetEventsInterface { private: CConnman* const connman; public: explicit PeerLogicValidation(CConnman* connman, CScheduler &scheduler); void BlockConnected(const std::shared_ptr& pblock, const CBlockIndex* pindexConnected, const std::vector& vtxConflicted) override; void UpdatedBlockTip(const CBlockIndex *pindexNew, const CBlockIndex *pindexFork, bool fInitialDownload) override; void BlockChecked(const CBlock& block, const CValidationState& state) override; void NewPoWValidBlock(const CBlockIndex *pindex, const std::shared_ptr& pblock) override; ........ };

这四个订阅者通过调用RegisterValidationInterfaceUnregisterValidationInterface 订阅,取消事件通知,函数接受参数是指向订阅者的指针。

void RegisterValidationInterface(CValidationInterface* pwalletIn) { g_signals.m_internals->UpdatedBlockTip.connect(boost::bind(&CValidationInterface::UpdatedBlockTip, pwalletIn, _1, _2, _3)); g_signals.m_internals->TransactionAddedToMempool.connect(boost::bind(&CValidationInterface::TransactionAddedToMempool, pwalletIn, _1)); g_signals.m_internals->BlockConnected.connect(boost::bind(&CValidationInterface::BlockConnected, pwalletIn, _1, _2, _3)); g_signals.m_internals->BlockDisconnected.connect(boost::bind(&CValidationInterface::BlockDisconnected, pwalletIn, _1)); g_signals.m_internals->TransactionRemovedFromMempool.connect(boost::bind(&CValidationInterface::TransactionRemovedFromMempool, pwalletIn, _1)); g_signals.m_internals->SetBestChain.connect(boost::bind(&CValidationInterface::SetBestChain, pwalletIn, _1)); g_signals.m_internals->Inventory.connect(boost::bind(&CValidationInterface::Inventory, pwalletIn, _1)); g_signals.m_internals->Broadcast.connect(boost::bind(&CValidationInterface::ResendWalletTransactions, pwalletIn, _1, _2)); g_signals.m_internals->BlockChecked.connect(boost::bind(&CValidationInterface::BlockChecked, pwalletIn, _1, _2)); g_signals.m_internals->NewPoWValidBlock.connect(boost::bind(&CValidationInterface::NewPoWValidBlock, pwalletIn, _1, _2)); } void UnregisterValidationInterface(CValidationInterface* pwalletIn) { g_signals.m_internals->BlockChecked.disconnect(boost::bind(&CValidationInterface::BlockChecked, pwalletIn, _1, _2)); g_signals.m_internals->Broadcast.disconnect(boost::bind(&CValidationInterface::ResendWalletTransactions, pwalletIn, _1, _2)); g_signals.m_internals->Inventory.disconnect(boost::bind(&CValidationInterface::Inventory, pwalletIn, _1)); g_signals.m_internals->SetBestChain.disconnect(boost::bind(&CValidationInterface::SetBestChain, pwalletIn, _1)); g_signals.m_internals->TransactionAddedToMempool.disconnect(boost::bind(&CValidationInterface::TransactionAddedToMempool, pwalletIn, _1)); g_signals.m_internals->BlockConnected.disconnect(boost::bind(&CValidationInterface::BlockConnected, pwalletIn, _1, _2, _3)); g_signals.m_internals->BlockDisconnected.disconnect(boost::bind(&CValidationInterface::BlockDisconnected, pwalletIn, _1)); g_signals.m_internals->TransactionRemovedFromMempool.disconnect(boost::bind(&CValidationInterface::TransactionRemovedFromMempool, pwalletIn, _1)); g_signals.m_internals->UpdatedBlockTip.disconnect(boost::bind(&CValidationInterface::UpdatedBlockTip, pwalletIn, _1, _2, _3)); g_signals.m_internals->NewPoWValidBlock.disconnect(boost::bind(&CValidationInterface::NewPoWValidBlock, pwalletIn, _1, _2)); }

在程序启动,初始化阶段,启动调度器线程

bool AppInitMain() { ................. CScheduler::Function serviceLoop = boost::bind(&CScheduler::serviceQueue, &scheduler); threadGroup.create_thread(boost::bind(&TraceThread, "scheduler", serviceLoop)); ................. }

调用RegisterBackgroundSignalScheduler(), 初始化全局MainSignalsInstance 实例; 调用RegisterWithMempoolSignals(), 订阅全局内存池对象的NotifyEntryRemoved 事件通知, MainSignalsInstance 只对由于超时,大小限制, blockchian 重组,替换等原因发生的离开内存池事件感兴趣, 收到后MainSignalsInstance 再作为事件发布者, 转发给其他订阅者, 如CWallet。

bool AppInitMain() { ...... GetMainSignals().RegisterBackgroundSignalScheduler(scheduler); GetMainSignals().RegisterWithMempoolSignals(mempool); ........ }

初始化全局的连接管理对象connman 后, 初始化全局的peerLogic 对象, 然后调用RegisterValidationInterface(), peerLogic 成为MainSignalsInstance 对象的订阅者, 如果用户编译了zeromq支持模块,调用RegisterValidationInterface(), pzmqNotificationInterface 订阅MainSignalsInstance 。

bool AppInitMain() { ............. assert(!g_connman); g_connman = std::unique_ptr(new CConnman(GetRand(std::numeric_limits<uint64_t>::max()), GetRand(std::numeric_limits<uint64_t>::max()))); CConnman& connman = *g_connman;
peerLogic.reset(new PeerLogicValidation(&connman, scheduler)); RegisterValidationInterface(peerLogic.get()); ............. #if ENABLE_ZMQ pzmqNotificationInterface = CZMQNotificationInterface::Create(); if (pzmqNotificationInterface) { RegisterValidationInterface(pzmqNotificationInterface); } #endif ............... }

如果钱包功能开启, 启动后打开钱包过程,会把钱包注册成为MainSignalsInstance的订阅者。

bool AppInitMain() { ........ #ifdef ENABLE_WALLET if (!OpenWallets()) return false; #else LogPrintf("No wallet support compiled in!
"); #endif ........ } bool OpenWallets() { if (gArgs.GetBoolArg("-disablewallet", DEFAULT_DISABLE_WALLET)) { LogPrintf("Wallet disabled!
"); return true; } for (const std::string& walletFile : gArgs.GetArgs("-wallet")) { CWallet * const pwallet = CWallet::CreateWalletFromFile(walletFile); if (!pwallet) { return false; } vpwallets.push_back(pwallet); } return true; }
CWallet* CWallet::CreateWalletFromFile(const std::string walletFile) { ...... CWallet *walletInstance = new CWallet(std::move(dbw)); RegisterValidationInterface(walletInstance); ...... }

submitblock rpc调用中, 用户提交hex编码的原始block, 解析后, 调用ProcessNewBlock()检查处理,使用类型submitblock_StateCatcher 的对象sc 作为MainSignalsInstance 的订阅者,
对提交过去的block 的验证结果,作为事件通知返回给rpc 调用。

UniValue submitblock(const JSONRPCRequest& request) { ........... submitblock_StateCatcher sc(block.GetHash()); RegisterValidationInterface(&sc); bool fAccepted = ProcessNewBlock(Params(), blockptr, true, nullptr); UnregisterValidationInterface(&sc); ........... }

CMainSignals 类型上面定义了一堆触发事件的方法, 别的代码模块调用这些方法, 触发相应的事件,把事件通知发给相关的订阅者。

void CMainSignals::UpdatedBlockTip(const CBlockIndex *pindexNew, const CBlockIndex *pindexFork, bool fInitialDownload) { m_internals->m_schedulerClient.AddToProcessQueue([pindexNew, pindexFork, fInitialDownload, this] { m_internals->UpdatedBlockTip(pindexNew, pindexFork, fInitialDownload); }); } void CMainSignals::TransactionAddedToMempool(const CTransactionRef &ptx) { m_internals->m_schedulerClient.AddToProcessQueue([ptx, this] { m_internals->TransactionAddedToMempool(ptx); }); } void CMainSignals::BlockConnected(const std::shared_ptr &pblock, const CBlockIndex *pindex, const std::shared_ptr>& pvtxConflicted) { m_internals->m_schedulerClient.AddToProcessQueue([pblock, pindex, pvtxConflicted, this] { m_internals->BlockConnected(pblock, pindex, *pvtxConflicted); }); } void CMainSignals::BlockDisconnected(const std::shared_ptr &pblock) { m_internals->m_schedulerClient.AddToProcessQueue([pblock, this] { m_internals->BlockDisconnected(pblock); }); } void CMainSignals::SetBestChain(const CBlockLocator &locator) { m_internals->m_schedulerClient.AddToProcessQueue([locator, this] { m_internals->SetBestChain(locator); }); } void CMainSignals::Inventory(const uint256 &hash) { m_internals->m_schedulerClient.AddToProcessQueue([hash, this] { m_internals->Inventory(hash); }); } void CMainSignals::Broadcast(int64_t nBestBlockTime, CConnman* connman) { m_internals->Broadcast(nBestBlockTime, connman); } void CMainSignals::BlockChecked(const CBlock& block, const CValidationState& state) { m_internals->BlockChecked(block, state); } void CMainSignals::NewPoWValidBlock(const CBlockIndex *pindex, const std::shared_ptr &block) { m_internals->NewPoWValidBlock(pindex, block); }

CChainState 的ActivateBestChain方法里, 发布BlockConnected, UpdatedBlockTip 事件:

bool CChainState::ActivateBestChain(CValidationState &state, const CChainParams& chainparams, std::shared_ptr pblock) { .............................. for (const PerBlockConnectTrace& trace : connectTrace.GetBlocksConnected()) { assert(trace.pblock && trace.pindex); GetMainSignals().BlockConnected(trace.pblock, trace.pindex, trace.conflictedTxs); } .............................. GetMainSignals().UpdatedBlockTip(pindexNewTip, pindexFork, fInitialDownload); ............................... }

CChainState 的AcceptBlock 方法里,发布NewPoWValidBlock 事件:

bool CChainState::AcceptBlock(const std::shared_ptr& pblock, CValidationState& state, const CChainParams& chainparams, CBlockIndex** ppindex, bool fRequested, const CDiskBlockPos* dbp, bool* fNewBlock) { ....................... if (!IsInitialBlockDownload() && chainActive.Tip() == pindex->pprev) GetMainSignals().NewPoWValidBlock(pindex, pblock); ...................... }

CChainState 的DisconnectTip 方法里,发布 BlockDisconnected 事件:

bool CChainState::DisconnectTip(CValidationState& state, const CChainParams& chainparams, DisconnectedBlockTransactions *disconnectpool) { ................... GetMainSignals().BlockDisconnected(pblock); .............. }

CChainState 的ConnectTip 方法里,发布 BlockChecked 事件:

bool CChainState::ConnectTip(CValidationState& state, const CChainParams& chainparams, CBlockIndex* pindexNew, const std::shared_ptr& pblock, ConnectTrace& connectTrace, DisconnectedBlockTransactions &disconnectpool) { ................ CCoinsViewCache view(pcoinsTip.get()); bool rv = ConnectBlock(blockConnecting, state, pindexNew, view, chainparams); GetMainSignals().BlockChecked(blockConnecting, state); ................ }

PeerLogicValidation 的 SendMessage 方法里, 发布Broadcast事件, 通知钱包重新发送未确认的交易:

bool PeerLogicValidation::SendMessages(CNode* pto, std::atomic& interruptMsgProc) { ............. if (!fReindex && !fImporting && !IsInitialBlockDownload()) { GetMainSignals().Broadcast(nTimeBestReceived, connman); } ............. }

从网络上收到INV消息后,通知给钱包,更新内部状态。

bool static ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStream& vRecv, int64_t nTimeReceived, const CChainParams& chainparams, CConnman* connman, const std::atomic& interruptMsgProc) { ................. for (CInv &inv : vInv) { ............ GetMainSignals().Inventory(inv.hash); } ................ }

validation.cpp 里面的 ProcessNewBlock在内部调用 CheckBlock 后,检查失败后,发布 BlockCheck s事件, 通告给相关订阅者。

bool ProcessNewBlock(const CChainParams& chainparams, const std::shared_ptr pblock, bool fForceProcessing, bool *fNewBlock) { ............ bool ret = CheckBlock(*pblock, state, chainparams.GetConsensus()); if (!ret) { GetMainSignals().BlockChecked(*pblock, state); return error("%s: AcceptBlock FAILED (%s)", __func__, state.GetDebugMessage()); } ........... }

FlushStateToDisk, 发布SetBestChain 事件, 通知钱包

bool static FlushStateToDisk(const CChainParams& chainparams, CValidationState &state, FlushStateMode mode, int nManualPruneHeight) { ............... if (fDoFullFlush || ((mode == FLUSH_STATE_ALWAYS || mode == FLUSH_STATE_PERIODIC) && nNow > nLastSetChain + (int64_t)DATABASE_WRITE_INTERVAL * 1000000)) { // Update best block in wallet (so we can detect restored wallets). GetMainSignals().SetBestChain(chainActive.GetLocator()); nLastSetChain = nNow; } ............... }

validation.cpp 里面的AcceptToMemoryPoolWorker, 在结束前, 发布TransactionAddedToMempool 事件。

static bool AcceptToMemoryPoolWorker(const CChainParams& chainparams, CTxMemPool& pool, CValidationState& state, const CTransactionRef& ptx, bool* pfMissingInputs, int64_t nAcceptTime, std::list* plTxnReplaced, bool bypass_limits, const CAmount& nAbsurdFee, std::vector& coins_to_uncache) { ................ GetMainSignals().TransactionAddedToMempool(ptx); }

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