我为我们即将推出的分布式 NoSQL 数据库系统制作了一个内部分布式时间服务器(没有主服务器)。只要分布式系统中 2/3 的时钟是正确的，它就应该处理拜占庭时钟和时钟偏差问题。

不过，我想看看其他人是如何实现这种模式的(对基于 IEEE 1588 的主/从模式实现不感兴趣)——最好是一些已经在使用的开源代码——以断言我已经正确实现它，因为很难为它编写单元测试。

有人知道这样的开源实现吗？我们使用 C++ 的编程语言，所以我更喜欢 C/C++ 引用，尽管它可能不是那么重要，只要代码是人类可读的。

这是我到目前为止的实现代码(为简单起见，部分伪代码):

/*!
\brief Maximum allowed clock skew in milliseconds
\details A network node that has a clock skew greater than this value will be ignore
* and an error message will be logged
\note Maximum divergence (drift) between two clocks on the network nodes will be 3x this amount if we 
* have a worst case Byzantium clock issue
*/
#define MAX_ALLOWED_CLOCK_SCEW_MS 333

/*!
\class CTimeServer
\brief Internal distributed time server
\details The time server frequently recieves the time from all the other master server nodes
* in the DBMS and calculates the current time by averaging all of the recieves timestamps.
\note If a server node has a greater clock skew than \c MAX_ALLOWED_CLOCK_SCEW_MS then it its
* timestamp is ignored and an error message is logged
\note Clocks are accurately synchronized until more than 1/3 of the nodes have Byzantium clock issues
\author Inge Eivind Henriksen
\date February 2014
*/
class CTimeServer
{
    private:
        /** System offset in milliseconds */
        std::atomic<int> offsetAverageMs;

        /*!
        \brief Node offsets type
        \par key Node ID
        \par value Offset in milliseconds
        */
        typedef std::map<int, int> nodeOffset_t;

        /*!
        \brief Iterator type for \c nodeOffset_t
        \relates nodeOffset_t
        */
        typedef nodeOffset_t::iterator nodeOffsetIter_t;

        /** Node offsets */
        nodeOffset_t nodeOffsets;

        /*!
        \brief Calculates the offset time in milliseconds between all the nodes in the distributed system
        */
        int CalculateOffsetMs() {
            bool exists;
            nodeOffsetIter_t offsets_iter(&nodeOffsets);
            int offsetMs = offsets_iter.first(&exists);
            int averageMs = 0;

            while (exists)
            {
                averageMs += offsetMs;
                averageMs /= 2;

                // Get the next file manager in the map
                offsetMs = offsets_iter.next(&exists);
            }

            return averageMs;
        }
    public:
        CTimeServer() {
            offsetAverageMs = 0;
        }

        /*!
        \brief Register the time of a node
        \param nodeHostName [in] Network node host name or IP address
        \param nodeId [in] Network node ID
        \param timestamp [in] Network node timestamp
        */
        void RegisterNodeTime(const wchar_t *nodeHostName, int nodeId, time_t timestamp) {
            int now = (int)time(NULL);
            int offset = (int)timestamp - now;

            // Make sure the node clock is within the permitted values
            if (abs(offset) > MAX_ALLOWED_CLOCK_SCEW_MS)
            {
                // Node clock skew was outside the permitted limit, so remove it from the list of valid time offsets
                nodeOffsets.erase(nodeId);

                // Throw an error
                std::wstringstream err;
                err << L"Network node " << nodeHostName << L" exceeded the maximum allowed clock skew of " 
                    << MAX_ALLOWED_CLOCK_SCEW_MS << L" ms by " << offset << " ms. Set the clock to correct this problem.";
                throw err.str().c_str();
            }

            nodeOffsets.update(nodeId, offset);

            // Recalculate the offset average
            offsetAverageMs.store(CalculateOffsetMs());
        }

        /*!
        \brief Get the distributed system time
        \returns The distributed system time
        */
        time_t GetTime() {
            int now = (int)time(NULL);
            return (time_t)(now + offsetAverageMs.load()));
        }

最佳答案

有大量关于时间同步协议(protocol)的文献，特别是对于无线传感器网络，其部署环境不适合时间掌握者。在 this page 上对该主题有一个不错的介绍。 .似乎最受关注的协议(protocol)是泛洪时间同步协议(protocol) (FTSP)，来自 paper。 Maróti、Kusy、Simon 和 Lédeczi 以这个名字命名。我在其 wiki 上找到了一个针对 TinyOS 的实现。 ，其中包含您正在寻找的代码类型。

对于任何无主系统都有一个警告:没有“正确”时间的概念。您可以获得的最好结果是将节点收敛到一个公共(public)时间引用。这是一个共识时间，但不应被视为权威的“正确”时间。

关于c++ - 内部分布式时间服务器实现，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/22065401/