Overview

High-performance logging is achieved with LoggerMessage. This class exposes functionality to create delegates that can be cached. This approach requires fewer object allocations and reduced computational overhead vs. ILogger.

Create a logger message

LoggerMessage.Define(LogLevel, EventId, String) configures an Action delegate that represents a log message. Each log message is stored in a static field created by Define.

private static readonly Action<ILogger, Exception> s_failedToProcessWorkItem;

The delegate is assigned:

s_failedToProcessWorkItem = LoggerMessage.Define(
    LogLevel.Critical,
    new EventId(13, nameof(FailedToProcessWorkItem)),
    "Epic failure processing item!");

Notes:

Define supports up to six type parameters.
Define’s String parameter uses message templates.

Extensions are defined:

public static class LoggerExtensions 
{
        public static void PriorityItemProcessed(this ILogger logger, WorkItem workItem) => 
            s_processingPriorityItem(logger, workItem, default!);

        public static void FailedToProcessWorkItem(this ILogger logger, Exception ex) => 
            s_failedToProcessWorkItem(logger, ex);

        public static IDisposable? ProcessingWorkScope(this ILogger logger, DateTime time) => 
            s_processingWorkScope(logger, time);
}

The delegates are invoked through their extension methods:

protected override async Task ExecuteAsync(
    CancellationToken stoppingToken)
{
    using IDisposable? scope = _logger.ProcessingWorkScope(DateTime.Now);

    while (!stoppingToken.IsCancellationRequested)
    {
        WorkItem? nextItem = _priorityQueue.ProcessNextHighestPriority();
        try
        {
            if (nextItem is not null)
                _logger.PriorityItemProcessed(nextItem);
        }
        catch (Exception ex)
        {
            _logger.FailedToProcessWorkItem(ex);
        }

        await Task.Delay(1_000, stoppingToken);
    }
}

Logger Message Scope

Use the DefineScope method.

Documentation: https://learn.microsoft.com/en-us/dotnet/core/extensions/high-performance-logging#define-logger-message-scope

Enhancing Further: Log Level Guarded Optimizations

Check the log level with ILogger.IsEnabled(LogLevel) before invoking a Log* method.

Documentation: https://learn.microsoft.com/en-us/dotnet/core/extensions/high-performance-logging#log-level-guarded-optimizations