RetryHelper 2.0.0

RetryHelper

This is a generic helper to help try some action until the given condition is met. It now works seamlessly with C# async/await keywords for asynchronous operations, which is very common in a scenario that requires retry logic.

Usage

Write retry logic for operations like web request or file operation in a more readable way rather than a try-catch nested in a loop. You can specify end conditions based on return value or exception, config the retry interval, maximum retry count and maximum retry time limitation.

Examples:

One-line example

RetryHelper.Instance.Try(() => TryDoSomething()).UntilNoException();

One-line async example

await RetryHelper.Instance.Try(async () => await TryGetValueAsync()).Until(async result => result < await GetQuota());

Example 1: Retry until I get a return value < 0.1 from the method TryGetValue.

// Basic usage
RetryHelper.Instance.Try(() => TryGetValue()).Until(result => result < 0.1);

// Get the result from the retried method
var resultSmallEnough = RetryHelper.Instance.Try(() => TryGetValue()).Until(result => result < 0.1);

// Specify interval
RetryHelper.Instance.Try(() => TryGetValue()).WithTryInterval(100).Until(result => result < 0.1);

// Specify max try count, will throw TimeoutException if exceeded
RetryHelper.Instance.Try(() => TryGetValue()).WithMaxTryCount(20).Until(result => result < 0.1);

// Can also constrain the total try time
RetryHelper.Instance.Try(() => TryGetValue()).WithTimeLimit(TimeSpan.FromSeconds(10)).Until(result => result < 0.1);

// Specify the extra success/fail/timeout action
RetryHelper.Instance.Try(() => TryGetValue())
    .WithMaxTryCount(20)
    .OnSuccess(result => Trace.TraceInformation($"Got result {result}."))
    .OnFailure(result => Trace.TraceWarning($"Try failed. Got {result}."))
    .OnTimeout(lastResult => Trace.TraceError("Did not get result under 0.1 in 20 times."))
    .Until(result => result < 0.1);

• OnSuccess: Executed after the condition is met.
• OnFailure: Executed after each failed attempt and before the next attempt.
• OnTimeout: Executed after all allowed attempts have failed.

Example 2: Retry method TryDoSomething until there's no exception thrown.

// Retry on any (non-fatal) exception
RetryHelper.Instance.Try(() => TryDoSomething()).UntilNoException();

// Retry on specific exception
RetryHelper.Instance.Try(() => TryDoSomething()).UntilNoException<ApplicationException>();

Example 3: Retry until I get a return value < 0.1 from an asynchronous method TryGetValueAsync

// Basic usage
await RetryHelper.Instance.Try(async () => await TryGetValueAsync()).Until(result => result < 0.1);

// async/await keywords can be omitted for simplicity in this case
await RetryHelper.Instance.Try(() => TryGetValueAsync()).Until(result => result < 0.1);

// Asynchronous until condition is also supported
await RetryHelper.Instance.Try(async () => await TryGetValueAsync()).Until(async result => result + await TryGetValueAsync() < 0.2);

// In case the operation is not asynchronous, but you want to use an asynchronous until condition, use TryAsync
await RetryHelper.Instance.TryAsync(() => TryGetValue()).Until(async result => result + await TryGetValueAsync() < 0.2);

// Asynchronous OnSuccess/OnFailure/OnTimeout
// Note that asyhronous operation taken in OnFailure counts against TimeLimit,
// i.e. when retrying with time limit, the more time taken in OnFailure, the less
// retries can be performed.
await RetryHelper.Instance.Try(async () => await TryGetValueAsync())
    .WithTryInterval(100)
    .WithMaxTryCount(20)
    .OnSuccess(async result => await LogToServerAsync($"Got result {result}."))
    .OnFailure(async result => await LogToServerAsync($"Try failed. Got {result}."))
    .OnTimeout(async lastResult => await LogToServerAsync("Did not get result under 0.1 in 20 times."))
    .Until(result => result < 0.1);

Change the global default settings

RetryHelper.Instance.DefaultMaxTryCount = 3;
RetryHelper.Instance.DefaultMaxTryTime = TimeSpan.FromSeconds(10);
RetryHelper.Instance.DefaultTryInterval = TimeSpan.FromMilliseconds(100);

Get another RetryHelper instance with custom TraceSource and unique configration

var retryHelper = new RetryHelper(new TraceSource("MyTraceSource"))
{
    DefaultMaxTryCount = 10,
    DefaultMaxTryTime = TimeSpan.FromSeconds(30),
    DefaultTryInterval = TimeSpan.FromMilliseconds(500),
};

Change Log

v2.0.0 (2018/5/17)

• Support asynchronous operations, conditions and callbacks (async/await keywords)
• Updated target framework to .NET 4.5
• Fixed a bug that OnFailure is not respected if not registed last

LICENSE

Apache 2.0 License