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Lamar and IDisposable/IAsyncDisposable

TIP

Lamar v7.0 added support for IAsyncDisposable handling. Finally.

One of the main reasons to use an IoC container is to offload the work of disposing created objects at the right time in the application scope. Sure, it's something you should be aware of, but developers are less likely to make mistakes if that's just handled for them. To simplify the usage of IDisposable and IAsyncDisposable. In summary, Lamar tracks all objects it creates in the container that created the object that implements either IDisposable or IAsyncDisposable, and these tracked objects are disposed when the creating container is disposed.

IAsyncDisposable

The Lamar IContainer itself, and all nested containers (scoped containers in .Net DI nomenclature) implement both IDisposable and IAsyncDisposable. It is not necessary to call both Dispose() and DisposeAsync() as either method will dispose all tracked IDisposable / IAsyncDisposable objects when either method is called.

cs
// Asynchronously disposing the container
await container.DisposeAsync();

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The following table explains what method is called on a tracked object when the creating container is disposed:

If an object implements...Container.Dispose()Container.DisposeAsync()
IDisposableDispose()Dispose()
IAsyncDisposableDisposeAsync().GetAwaiter().GetResult()DisposeAsync()
IDisposable and IAsyncDisposableDisposeAsync()DisposeAsync()

If any objects are being created by Lamar that only implement IAsyncDisposable, it is probably best to strictly use Container.DisposeAsync() to avoid any problematic mixing of sync and async code.

Singletons

This one is easy, any object marked as the Singleton lifecycle that implements IDisposable is disposed when the root container is disposed:

cs
[Fact]
public void singletons_are_disposed_when_the_container_is_disposed()
{
    var container = new Container(_ =>
    {
        _.ForSingletonOf<DisposableSingleton>();
    });

    // As a singleton-scoped object, every request for DisposableSingleton
    // will return the same object
    var singleton = container.GetInstance<DisposableSingleton>();
    singleton.ShouldBeSameAs(container.GetInstance<DisposableSingleton>());
    singleton.ShouldBeSameAs(container.GetInstance<DisposableSingleton>());
    singleton.ShouldBeSameAs(container.GetInstance<DisposableSingleton>());
    singleton.ShouldBeSameAs(container.GetInstance<DisposableSingleton>());

    singleton.WasDisposed.ShouldBeFalse();

    // now, dispose the Container
    container.Dispose();

    // the SingletonThing scoped object should be disposed
    singleton.WasDisposed.ShouldBeTrue();
}

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Nested Containers

As discussed in nested containers, any transient or container-scoped object that implements IDisposable and is created by a nested container will be disposed as the nested container is disposed:

cs
[Fact]
public void nested_container_disposal()
{
    var container = new Container(_ =>
    {
        // A SingletonThing scoped service
        _.ForSingletonOf<IColorCache>().Use<ColorCache>();

        // A transient scoped service
        _.For<IColor>().Use<Green>();

        // An AlwaysUnique scoped service
        _.AddTransient<Purple>();

        _.AddTransient<Blue>();
    });

    ColorCache singleton = null;
    Green nestedGreen = null;
    Blue nestedBlue = null;
    Purple nestedPurple = null;

    using (var nested = container.GetNestedContainer())
    {
        // SingletonThing's are really built by the parent
        singleton = nested.GetInstance<IColorCache>()
            .ShouldBeOfType<ColorCache>();

        nestedGreen = nested.GetInstance<IColor>()
            .ShouldBeOfType<Green>();

        nestedBlue = nested.GetInstance<Blue>();

        nestedPurple = nested.GetInstance<Purple>();
    }

    // Transients created by the Nested Container
    // are disposed
    nestedGreen.WasDisposed.ShouldBeTrue();
    nestedBlue.WasDisposed.ShouldBeTrue();

    // Unique's created by the Nested Container
    // are disposed
    nestedPurple.WasDisposed.ShouldBeTrue();

    // NOT disposed because it's owned by
    // the parent container
    singleton.WasDisposed.ShouldBeFalse();
}

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cs
[Fact]
public void nested_container_disposal()
{
    var container = new Container(_ =>
    {
        // A SingletonThing scoped service
        _.ForSingletonOf<IColorCache>().Use<ColorCache>();

        // A transient scoped service
        _.For<IColor>().Use<Green>();

        // An AlwaysUnique scoped service
        _.For<Purple>().AlwaysUnique();
    });

    ColorCache singleton = null;
    Green nestedGreen = null;
    Blue nestedBlue = null;
    Purple nestedPurple = null;

    using (var nested = container.GetNestedContainer())
    {
        // SingletonThing's are really built by the parent
        singleton = nested.GetInstance<IColorCache>()
            .ShouldBeOfType<ColorCache>();

        nestedGreen = nested.GetInstance<IColor>()
            .ShouldBeOfType<Green>();

        nestedBlue = nested.GetInstance<Blue>();

        nestedPurple = nested.GetInstance<Purple>();
    }

    // Transients created by the Nested Container
    // are disposed
    nestedGreen.WasDisposed.ShouldBeTrue();
    nestedBlue.WasDisposed.ShouldBeTrue();

    // Unique's created by the Nested Container
    // are disposed
    nestedPurple.WasDisposed.ShouldBeTrue();

    // NOT disposed because it's owned by
    // the parent container
    singleton.WasDisposed.ShouldBeFalse();
}

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Transients

WARNING

This behavior is different from StructureMap. Be aware of this, or you may be vulnerable to memory leaks.

Objects that implement IDisposable are tracked by the container that creates them and will be disposed whenever that container itself is disposed.