Be Lazy, but be ware of initialization exception

You can become a serverless blackbelt. Enrol in my course Learn you some Lambda best practice for great good! and learn best practices for performance, cost, security, resilience, observability and scalability. By the end of this course, you should be able to make informed decisions on which AWS service to use with Lambda and how to build highly scalable, resilient and cost efficient serverless applications.

.Net 4 introduced the Lazy<T> type which allows you to create an object that can be lazily initialized so that you can delay the creation of large objects, for instance.

However, if your initialization logic has the potential to except at runtime (e.g. time out exceptions reading from some external data source) then you should pay close attention to which constructor you use to create a new instance of the Lazy<T> type. Depending on the selected LazyThreadSafetyMode, exceptions in the initialization code might be cached and rethrown on all subsequent attempts to fetch the lazily initialized value. Whilst this ensures that threads will always get the same result, hence removing ambiguity, it does mean that you’ve got only one shot at initializing that value…

 

LazyThreadSafetyMode

In cases where you need to be able to tolerate occasional initialization errors (e.g. reading a large object from S3 can fail from time to time for a number of reasons) and be able to try again at a second attempt, the rule of thumb is to instantiate the Lazy<T> type by setting LazyThreadSafetyMode to PublicationOnly. In PublicationOnly thread safety mode, multiple threads can invoke the initialization logic but the first thread to complete the initialization successfully sets the value of the Lazy<T> instance.

For example, the following only works under the PublicationOnly mode:

 

F#

F# provides a slightly nicer syntax for defining a lazy computation:

image

the Control.Lazy<T> type is an abbreviation of the BCL Lazy<T> type with a Force extension method which under the hood just calls Lazy<T>.Value.

Presumably the above translates roughly to the following C# code:

var x = 10;

var result = new Lazy<int>(() => x + 10);

and the thread safety mode using the Lazy(Func<T>) constructor is LazyThreadSafetyMode.ExecutionAndPublication which caches and rethrows any exceptions caught in the initialization. E.g.:

image

Liked this article? Support me on Patreon and get direct help from me via a private Slack channel or 1-2-1 mentoring.
Subscribe to my newsletter


Hi, I’m Yan. I’m an AWS Serverless Hero and the author of Production-Ready Serverless.

I specialise in rapidly transitioning teams to serverless and building production-ready services on AWS.

Are you struggling with serverless or need guidance on best practices? Do you want someone to review your architecture and help you avoid costly mistakes down the line? Whatever the case, I’m here to help.

Hire me.


Check out my new podcast Real-World Serverless where I talk with engineers who are building amazing things with serverless technologies and discuss the real-world use cases and challenges they face. If you’re interested in what people are actually doing with serverless and what it’s really like to be working with serverless day-to-day, then this is the podcast for you.


Check out my new course, Learn you some Lambda best practice for great good! In this course, you will learn best practices for working with AWS Lambda in terms of performance, cost, security, scalability, resilience and observability. We will also cover latest features from re:Invent 2019 such as Provisioned Concurrency and Lambda Destinations. Enrol now and start learning!


Check out my video course, Complete Guide to AWS Step Functions. In this course, we’ll cover everything you need to know to use AWS Step Functions service effectively. There is something for everyone from beginners to more advanced users looking for design patterns and best practices. Enrol now and start learning!


Are you working with Serverless and looking for expert training to level-up your skills? Or are you looking for a solid foundation to start from? Look no further, register for my Production-Ready Serverless workshop to learn how to build production-grade Serverless applications!

Find a workshop near you