Async Expiring Lazy

See blog article for more background details and a follow up post for further update.

Installation

Grab the Nuget package called Strathweb.AsyncExpiringLazy. It is cross compiled for .NET Standard 1.1, .NET Standard 2.0 and .NET Framework 4.6.1 and compatible with:

• .NET Framework 4.6.1
• all version of .NET Core
• Xamarin
• Mono
• Universal Windows Platform

Latest version:

Usage

The code sample shows creating a lazy epxiring value with AsyncExpiringLazy<T> and letting it get recreated on first reuse after expiration.

var testInstance = new AsyncExpiringLazy<TokenResponse>(async metadata =>
{
    await Task.Delay(1000);
    return new ExpirationMetadata<TokenResponse>
    {
        Result = new TokenResponse
        {
            AccessToken = Guid.NewGuid().ToString()
        }, ValidUntil = DateTimeOffset.UtcNow.AddSeconds(2)
    };
});

// 1. check if value is created - shouldn't
Assert.False(await testInstance.IsValueCreated());

// 2. fetch lazy expiring value
var token = await testInstance.Value();

// 3a. verify it is created now
Assert.True(await testInstance.IsValueCreated());

// 3b. verify it is not null
Assert.NotNull(token.AccessToken);

// 4. fetch the value again. Since it's lifetime is 2 seconds, it should be still the same
var token2 = await testInstance.Value();
Assert.Same(token, token2);

// 5. sleep for 2 seconds to let the value expire
await Task.Delay(2000);

// 6a. verify the value expired
Assert.False(await testInstance.IsValueCreated());

// 6b. fetch again
var token3 = await testInstance.Value();

// 7. verify we now have a new (recreated) value - as the previous one expired
Assert.NotSame(token2, token3);

// 8. invalidate the value manually before it has a chance to expire
await testInstance.Invalidate();

// 9. check if value is created - shouldn't anymore
Assert.False(await testInstance.IsValueCreated());

The next code sample shows creating a lazy epxiring value with AsyncExpiringEager<T> and letting it get recreated silently as soon as it expires. Pay attetion to the different from the previous example at step 6a.

using var testInstance = new AsyncExpiringEager<TokenResponse>(async metadata =>
{
    await Task.Delay(1000);
    return new ExpirationMetadata<TokenResponse>
    {
        Result = new TokenResponse
        {
            AccessToken = Guid.NewGuid().ToString()
        }, ValidUntil = DateTimeOffset.UtcNow.AddSeconds(2)
    };
});

// 1. check if value is created - shouldn't
Assert.False(testInstance.IsValueCreated());

// 2. fetch lazy expiring value
var token = await testInstance.Value();

// 3a. verify it is created now
Assert.True(testInstance.IsValueCreated());

// 3b. verify it is not null
Assert.NotNull(token.AccessToken);

// 4. fetch the value again. Since it's lifetime is 2 seconds, it should be still the same
var token2 = await testInstance.Value();
Assert.Same(token, token2);

// 5. sleep for 2 seconds to let the value expire
await Task.Delay(2000);

// 6a. verify the value was eagerly created just before it expired
Assert.True(testInstance.IsValueCreated());

// 6b. fetch again
var token3 = await testInstance.Value();

// 7. verify we now have a new (recreated) value - as the previous one expired
Assert.NotSame(token2, token3);

// 8. invalidate the value manually before it has a chance to expire
testInstance.Invalidate();

// 9. check if value is created - shouldn't anymore
Assert.False(testInstance.IsValueCreated());

License

MIT