比特币源码分析-boost::signal的使用
2018-03-08 本文已影响60人
姜家志
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connect， disconnect 方法分别相当于对事件的订阅，取消。
#include <boost/signals2.hpp>
#include <iostream>
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<MainSignalsInstance> m_internals;
friend void ::RegisterValidationInterface(CValidationInterface*);
friend void ::UnregisterValidationInterface(CValidationInterface*);
friend void ::UnregisterAllValidationInterfaces();
friend void ::CallFunctionInValidationInterfaceQueue(std::function<void ()> 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 CBlock> &, const CBlockIndex *pindex, const std::shared_ptr<const std::vector<CTransactionRef>> &);
void BlockDisconnected(const std::shared_ptr<const CBlock> &);
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<const CBlock>&);
};
struct MainSignalsInstance {
boost::signals2::signal<void (const CBlockIndex *, const CBlockIndex *, bool fInitialDownload)> UpdatedBlockTip;
boost::signals2::signal<void (const CTransactionRef &)> TransactionAddedToMempool;
boost::signals2::signal<void (const std::shared_ptr<const CBlock> &, const CBlockIndex *pindex, const std::vector<CTransactionRef>&)> BlockConnected;
boost::signals2::signal<void (const std::shared_ptr<const CBlock> &)> BlockDisconnected;
boost::signals2::signal<void (const CTransactionRef &)> TransactionRemovedFromMempool;
boost::signals2::signal<void (const CBlockLocator &)> SetBestChain;
boost::signals2::signal<void (const uint256 &)> Inventory;
boost::signals2::signal<void (int64_t nBestBlockTime, CConnman* connman)> Broadcast;
boost::signals2::signal<void (const CBlock&, const CValidationState&)> BlockChecked;
boost::signals2::signal<void (const CBlockIndex *, const std::shared_ptr<const CBlock>&)> 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<const CBlock> &block, const CBlockIndex *pindex, const std::vector<CTransactionRef> &txnConflicted) {}
virtual void BlockDisconnected(const std::shared_ptr<const CBlock> &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<const CBlock>& 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<const CBlock>& pblock, const CBlockIndex *pindex, const std::vector<CTransactionRef>& vtxConflicted) override;
void BlockDisconnected(const std::shared_ptr<const CBlock>& 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<const CBlock>& pblock, const CBlockIndex* pindexConnected, const std::vector<CTransactionRef>& vtxConflicted) override;
void BlockDisconnected(const std::shared_ptr<const CBlock>& 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<const CBlock>& pblock, const CBlockIndex* pindexConnected, const std::vector<CTransactionRef>& 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<const CBlock>& pblock) override;
........
};
这四个订阅者通过调用RegisterValidationInterface， UnregisterValidationInterface 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<CScheduler::Function>, "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<CConnman>(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!\n");
#endif
........
}
bool OpenWallets()
{
if (gArgs.GetBoolArg("-disablewallet", DEFAULT_DISABLE_WALLET)) {
LogPrintf("Wallet disabled!\n");
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);
......
}
在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<const CBlock> &pblock, const CBlockIndex *pindex, const std::shared_ptr<const std::vector<CTransactionRef>>& pvtxConflicted) {
m_internals->m_schedulerClient.AddToProcessQueue([pblock, pindex, pvtxConflicted, this] {
m_internals->BlockConnected(pblock, pindex, *pvtxConflicted);
});
}
void CMainSignals::BlockDisconnected(const std::shared_ptr<const CBlock> &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<const CBlock> &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<const CBlock> 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<const CBlock>& 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<const CBlock>& 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<bool>& 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<bool>& 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<const CBlock> 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<CTransactionRef>* plTxnReplaced,
bool bypass_limits, const CAmount& nAbsurdFee, std::vector<COutPoint>& coins_to_uncache)
{
................
GetMainSignals().TransactionAddedToMempool(ptx);
}
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