Class Encoder

runtime/Log.h:635–688

* Encapsulates the knowledge on how to transform UncompresedLogMessage's * created by the generated code into a compressed log for a Decoder * object to interpret later. * * The intended usage pattern is for the user to create an Encoder object * per compressed log file that they intend to create, feed it a character * buffer array to operate on, and repeatedly invoke

     *  - Log Messages live within BufferExtents and do not span BufferExtents.
     */
    class Encoder {
    PUBLIC:
        Encoder(char *buffer, size_t bufferSize,
                bool skipCheckpoint=false,
                bool forceDictionaryOutput=false);

        long encodeLogMsgs(char *from, uint64_t nbytes,
                           uint32_t bufferId,
                           bool wrapAround,
                           uint64_t *numEventsCompressed);

        long encodeLogMsgs(char *from, uint64_t nbytes,
                                    uint32_t bufferId,
                                    bool wrapAround,
                                    std::vector<StaticLogInfo> dictionary,
                                    uint64_t *numEventsCompressed);
        uint32_t encodeNewDictionaryEntries(uint32_t& currentPosition,
                                            std::vector<StaticLogInfo> allMetadata);

        size_t getEncodedBytes();
        void swapBuffer(char *inBuffer, size_t inSize,
                        char **outBuffer=nullptr, size_t *outLength=nullptr,
                        size_t *outSize=nullptr);

    PRIVATE:
        bool encodeBufferExtentStart(uint32_t bufferId, bool wrapAround);

        // Used to store the compressed log messages and related metadata
        char *backing_buffer;

        // Position within the backing_buffer where the next log entries or
        // log metadata should be placed.
        char *writePos;

        // Marks the first invalid byte in the backing_buffer
        char *endOfBuffer;

        // Saves the last bufferId encoded to determine when a new BufferExtent
        // needs to be encoded. A value of (-1) indicates no extent was encoded.
        uint32_t lastBufferIdEncoded;

        // A pointer to the last encoded BufferExtent's length to allow updating
        // the value as the user performs more encodeLogMsgs with the same id.
        uint32_t *currentExtentSize;

        // Metric: Total number of encode failures due to missing metadata. This
        // is typically due to a benign race condition, but could indicate an
        // error if it happens repeatedly.
        uint32_t encodeMissDueToMetadata;

        // Metric: Number of consecutive encode failures due to missing metadata
        // Used to detect cases where the dictionary isn't persisted due to bugs
        uint32_t consecutiveEncodeMissesDueToMetadata;
    };

    /**
     * This class embodies a runtime log statement returned from