Logging Services

The OnixS::CME::MDH::Logger abstraction receives log entries produced by handlers and Feed Engines. A Handler and an explicitly constructed Feed Engine select their loggers independently; assigning a logger to one does not configure the other.

Default Logging Behavior

By default, a Handler uses the library-managed file logger, which writes to OnixS.CmeMdpPremiumCppHandlers.log. Passing nullptr to OnixS::CME::MDH::LoggingSettings::logger selects this default again. To disable Handler logging, bind an OnixS::CME::MDH::NullLogger explicitly.

Socket and Solarflare Feed Engines default to OnixS::CME::MDH::NullLogger. To capture events from an explicitly constructed Feed Engine, set the logger through OnixS::CME::MDH::NetFeedEngineSettings::logger before constructing the engine. Passing nullptr selects the Feed Engine's default OnixS::CME::MDH::NullLogger again.

Ready-to-use Logger Implementations

The SDK contains the following implementations of the OnixS::CME::MDH::Logger abstraction:

• OnixS::CME::MDH::FileLogger writes entries to a text file. The file may be limited by size; once it reaches the configured limit, the logger rolls it over and starts a new file.
• OnixS::CME::MDH::NullLogger discards all entries. Bind it explicitly to a Handler to disable Handler logging.

Note

A logger instance can be shared by multiple handlers and Feed Engines. These components do not manage its lifetime; keep the logger alive until every component using it has been destroyed.

Binding a Logger to the Handler and Feed Engine

The following example configures one file logger for both a Handler and an explicit Socket Feed Engine. OnixS::CME::MDH::SolarflareFeedEngineSettings supports the same logger setting.

struct FileLoggerIssueTracer : public FileLoggerListener
{
    void onFileLoggerIssue(const FileLogger& logger, const Messaging::Char* issue) override
    {
        std::cout << "ALERT!!! An issue occurred while logging data. " << issue << std::endl;
    }
};
 
FileLoggerSettings loggerSettings;
loggerSettings.filename(makeLogFilename(310));
loggerSettings.severityLevel(LogSeverity::Debug);
 
FileLoggerIssueTracer loggerTracer;
FileLogger logger(loggerSettings, &loggerTracer);
 
SocketFeedEngineSettings feedEngineSettings;
feedEngineSettings.logger(&logger);
SocketFeedEngine feedEngine(feedEngineSettings);
 
Handler handler;
handler.settings().channel(310).connectivityConfigurationFile("config.xml")
                  .logging().debug().traceMessages(MessageTracing::SbeFormat);
handler.settings().feeds().engine(&feedEngine);
handler.settings().logging().logger(&logger);