蹭蹭热度，研究一下区块链和bitcoin，还是Linus的话：

talk is cheap , show me the code 

想要分析原理的话，推荐图书： 区块链原理、设计与应用

git bitcoin源码：

git clone https://github.com/bitcoin/bitcoin.git

安装编译环境和依赖包：

sudo apt-get install software-properties-common

sudo add-apt-repository ppa:bitcoin/bitcoin

sudo apt-get update

sudo apt-get install build-essential libtool autotools-dev autoconf pkg-config libssl-dev libevent-dev

sudo apt-get install libboost-all-dev

sudo apt-get install libdb4.8-dev libdb4.8++-dev

sudo apt-get install libminiupnpc-dev

sudo apt-get install libprotobuf-dev protobuf-compiler

sudo apt-get install libqrencode-dev

可以看到bitcoin是C++代码，通过boost库实现，
编译：

   ./autogen.sh
  ./configure
  make 

这时会生成bitcoind 可执行文件， 结尾为加d一般都是指daemon程序，看源码：

int main(int argc, char* argv[])
{
    SetupEnvironment(); //该函数设置了本地运行环境

    // Connect bitcoind signal handlers
    noui_connect();   //连接bitcoind客户端的信号处理程序

    return (AppInit(argc, argv) ? EXIT_SUCCESS : EXIT_FAILURE);
}

AppInit(argc, argv)进入主程序，开始应用程序初始化。
AppInit()包含东西较多，简单的分成两块，一块是系统配置和参数解析，一块进入到实际操作AppInitMain：

 fRet = AppInitMain(); 

AppInitMain中，首先获取bitcoin.conf文件中的配置，没有配置的则设置为默认值：

if (!fLogTimestamps)
        LogPrintf("Startup time: %s\n", FormatISO8601DateTime(GetTime()));
    LogPrintf("Default data directory %s\n", GetDefaultDataDir().string());
    LogPrintf("Using data directory %s\n", GetDataDir().string());
    LogPrintf("Using config file %s\n", GetConfigFile(gArgs.GetArg("-conf", BITCOIN_CONF_FILENAME)).string());
    LogPrintf("Using at most %i automatic connections (%i file descriptors available)\n", nMaxConnections, nFD);

    // Warn about relative -datadir path.
    if (gArgs.IsArgSet("-datadir") && !fs::path(gArgs.GetArg("-datadir", "")).is_absolute()) {
        LogPrintf("Warning: relative datadir option '%s' specified, which will be interpreted relative to the " /* Continued */
                  "current working directory '%s'. This is fragile, because if bitcoin is started in the future "
                  "from a different location, it will be unable to locate the current data files. There could "
                  "also be data loss if bitcoin is started while in a temporary directory.\n",
            gArgs.GetArg("-datadir", ""), fs::current_path().string());
    }

然后初始化各个线程并运行：

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

    GetMainSignals().RegisterBackgroundSignalScheduler(scheduler);
    GetMainSignals().RegisterWithMempoolSignals(mempool);

注册rpc命令并启动rpc服务：

* Register RPC commands regardless of -server setting so they will be
     * available in the GUI RPC console even if external calls are disabled.
     */
    RegisterAllCoreRPCCommands(tableRPC);
    g_wallet_init_interface.RegisterRPC(tableRPC);

    /* Start the RPC server already.  It will be started in "warmup" mode
     * and not really process calls already (but it will signify connections
     * that the server is there and will be ready later).  Warmup mode will
     * be disabled when initialisation is finished.
     */
    if (gArgs.GetBoolArg("-server", false))
    {
        uiInterface.InitMessage.connect(SetRPCWarmupStatus);
        if (!AppInitServers())
            return InitError(_("Unable to start HTTP server. See debug log for details."));
    }

然后验证钱包数据库：

    // ********************************************************* Step 5: verify wallet database integrity
    if (!g_wallet_init_interface.Verify()) return false;

之后，进程网络初始化和连接，基本都是各种网络参数和不通类型的网络服务的配置。
加入网络后，下一步开始加载区块链

 ********************************************************* Step 7: load block chain

    fReindex = gArgs.GetBoolArg("-reindex", false);
    bool fReindexChainState = gArgs.GetBoolArg("-reindex-chainstate", false);

    // cache size calculations
    int64_t nTotalCache = (gArgs.GetArg("-dbcache", nDefaultDbCache) << 20);
    nTotalCache = std::max(nTotalCache, nMinDbCache << 20); // total cache cannot be less than nMinDbCache
    nTotalCache = std::min(nTotalCache, nMaxDbCache << 20); // total cache cannot be greater than nMaxDbcache
    int64_t nBlockTreeDBCache = std::min(nTotalCache / 8, nMaxBlockDBCache << 20);
    nTotalCache -= nBlockTreeDBCache;
    int64_t nTxIndexCache = std::min(nTotalCache / 8, gArgs.GetBoolArg("-txindex", DEFAULT_TXINDEX) ? nMaxTxIndexCache << 20 : 0);
    nTotalCache -= nTxIndexCache;
    int64_t nCoinDBCache = std::min(nTotalCache / 2, (nTotalCache / 4) + (1 << 23)); // use 25%-50% of the remainder for disk cache
    nCoinDBCache = std::min(nCoinDBCache, nMaxCoinsDBCache << 20); // cap total coins db cache
    nTotalCache -= nCoinDBCache;
    nCoinCacheUsage = nTotalCache; // the rest goes to in-memory cache
    int64_t nMempoolSizeMax = gArgs.GetArg("-maxmempool", DEFAULT_MAX_MEMPOOL_SIZE) * 1000000;
    LogPrintf("Cache configuration:\n");
    LogPrintf("* Using %.1fMiB for block index database\n", nBlockTreeDBCache * (1.0 / 1024 / 1024));
    if (gArgs.GetBoolArg("-txindex", DEFAULT_TXINDEX)) {
        LogPrintf("* Using %.1fMiB for transaction index database\n", nTxIndexCache * (1.0 / 1024 / 1024));
    }
    LogPrintf("* Using %.1fMiB for chain state database\n", nCoinDBCache * (1.0 / 1024 / 1024));
    LogPrintf("* Using %.1fMiB for in-memory UTXO set (plus up to %.1fMiB of unused mempool space)\n", nCoinCacheUsage * (1.0 / 1024 / 1024), nMempoolSizeMax * (1.0 / 1024 / 1024));

加载完成后，进入挖矿阶段， while循环

挖掘成功后，按照钱包地址，加载钱包，进行一系列修改和配置

// if pruning, unset the service bit and perform the initial blockstore prune
    // after any wallet rescanning has taken place.
    if (fPruneMode) {
        LogPrintf("Unsetting NODE_NETWORK on prune mode\n");
        nLocalServices = ServiceFlags(nLocalServices & ~NODE_NETWORK);
        if (!fReindex) {
            uiInterface.InitMessage(_("Pruning blockstore..."));
            PruneAndFlush();
        }
    }

产生新的block之后，创建新节点：

CConnman::Options connOptions;
    connOptions.nLocalServices = nLocalServices;
    connOptions.nMaxConnections = nMaxConnections;
    connOptions.nMaxOutbound = std::min(MAX_OUTBOUND_CONNECTIONS, connOptions.nMaxConnections);
    connOptions.nMaxAddnode = MAX_ADDNODE_CONNECTIONS;
    connOptions.nMaxFeeler = 1;
    connOptions.nBestHeight = chain_active_height;
    connOptions.uiInterface = &uiInterface;
    connOptions.m_msgproc = peerLogic.get();
    connOptions.nSendBufferMaxSize = 1000*gArgs.GetArg("-maxsendbuffer", DEFAULT_MAXSENDBUFFER);
    connOptions.nReceiveFloodSize = 1000*gArgs.GetArg("-maxreceivebuffer", DEFAULT_MAXRECEIVEBUFFER);
    connOptions.m_added_nodes = gArgs.GetArgs("-addnode");

    connOptions.nMaxOutboundTimeframe = nMaxOutboundTimeframe;
    connOptions.nMaxOutboundLimit = nMaxOutboundLimit;

新的节点创建完成并加入到区块链中，完成！