Compile-time logging source generation for highly performant logging

The Background

In the world of .NET software development, logging is a crucial part of keeping track of what's happening inside your applications. It helps you find and fix issues, understand how your software is behaving, and ensure it runs smoothly. With the release of .NET 6, there's a new tool in town called LoggerMessageAttribute , and it's here to make logging better and easier. It's a part of the Microsoft.Extensions.Logging family, and when you use it, it generates super-efficient code for logging. This means your application can log things much faster, which is great for performance. Imagine you're writing code and you want to log something. Instead of writing a bunch of code to set up the logging, you just add this attribute to a  partial method, and LoggerMessageAttribute does the heavy lifting for you. It's like having a personal assistant for your logging tasks! Let's take a look...

Basic usage

To utilize the LoggerMessageAttribute, both the consuming class and the associated method must be declared as partial . During compilation, the code generator is activated and produces an implementation for the partial method. Let's see an example:

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public static partial class Log{   [LoggerMessage(      EventId = 0,      Level = LogLevel.Critical,      Message = "Could not open socket to `{HostName}`")   ]   public static partial void CouldNotOpenSocket(      ILogger logger, string hostName);}

In the example provided earlier, the logging method is static, and the log level is set within the attribute definition. If you intend to use the attribute in a static context, you have two options: either include the ILogger instance as a parameter, or adjust the method's definition by using the 'this' keyword to convert it into an extension method. Alternatively, you have the flexibility to employ the attribute within a non-static context. Take the following example, where the logging method is defined as an instance method. In this scenario, the method obtains the logger by accessing an ILogger field within the enclosing class:

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public partial class InstanceLoggingExample{   private readonly ILogger _logger;    public InstanceLoggingExample(ILogger logger)   {      _logger = logger;   }    [LoggerMessage(      EventId = 0,      Level = LogLevel.Critical,      Message = "Could not open socket to `{HostName}`")   ]   public partial void CouldNotOpenSocket(string hostName);}

Dynamic Log Level

At times, you might want the log level to be flexible and not hardcoded into your code. To achieve this, you can leave out the log level in the attribute and, instead, make it something you need to provide as a parameter when using the logging method:

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public static partial class Log{   [LoggerMessage(      EventId = 0,      Message = "Could not open socket to `{HostName}`")   ]   public static partial void CouldNotOpenSocket(      ILogger logger,      LogLevel level, /* Dynamic log level as parameter, rather than defined in attribute. */      string hostName);}

Log method constraints

When using the LoggerMessageAttribute on logging methods, some constraints must be followed: • Logging methods must be partial and return void . • Logging method names must not start with an underscore. • Parameter names of logging methods must not start with an underscore. • Logging methods may not be defined in a nested type. • Logging methods cannot be generic. • If a logging method is static , the ILogger instance is required as a parameter.

Conslusion

In summary, the LoggerMessageAttribute in .NET 6 simplifies and accelerates the process of creating high-performance logging code. By automatically generating LoggerMessage.Define calls and optimizing the generated code for performance, it helps developers produce efficient and reliable logging solutions with minimal effort. This attribute is a valuable addition to the .NET logging ecosystem, contributing to better logging practices in modern .NET applications. That's all from me today.

For more logging practices, see Structured Logging with Serilog and Monitoring .NET Applications.

Wrapping Up

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