Lifetime of object created to call non-static Azure Function

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Lifetime of object created to call non-static Azure Function

Buck I 36

I'm writing Azure Functions where the functions are non-static methods (in non-static classes, of course), so that I can use dependency injection. One thing I'm not clear on is the lifetime of the object that the methods are called on. Is it guaranteed that the framework creates a new object of your class each time one of the functions is triggered, or are objects re-used?

Specifically, if a new object is created each time it means that 1) dependencies are resolved each time; 2) the object is always a "fresh" newly-constructed one when your function is called; and 3) it is safe to store things in the object that only pertain to the that invocation of your Azure Function. Are those things true?

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Answer 1

MikeUrnun 9,777 Moderator

Hi @Buck I

You may have already read & reviewed in the doc but the lifetimes of dependency services are inherently the same ones defined in the ASP.NET Dependency injection: Transient - instance per constructor injection, Scoped - instance per execution (function invocation), and Singleton - per process, which are called as follows:

builder.Services.AddTransient<IOperationTransient, Operation>();  
builder.Services.AddScoped<IOperationScoped, Operation>();  
builder.Services.AddSingleton<IOperationSingleton, Operation>();

You would then need to choose the lifetime that is the best fit for the particular service that's being registered in your Startup.cs file and how would use it later on in your function.

Buck I 36 Reputation points

2021-05-11T13:16:48.63+00:00

Right, I understand that, but what I'm asking about is not the lifetime of the injected services, but the lifetime of the object they are injected into (which, it's true, does then indirectly affect the lifetime of the injected services).

So for instance, as you mentioned, a transient service is created once per constructor injection. But when does the object get constructed? To use dependency injection, you create your own class (let's call it MyClass) that uses constructor injection and has a method that is your Azure function (call it MyFunction). Does Azure Functions create a new MyClass each time MyFunction is triggered, or does it create a MyClass then potentially call MyFunction on it multiple times as MyFunction is triggered multiple times? In the first case, MyFunction sees a new instance of a transient service each time; in the second case, multiple calls to MyFunction see the same instance of the transient function.

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Lifetime of object created to call non-static Azure Function

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