Specifying Retry Strategies in Code

You do not need to define your retry strategies in a configuration file. In scenarios, with a small number of operations that require retry logic, it may be quicker to define the all of the retry policy in code.

The following code sample shows how you can define your retry strategy, create a retry policy, and use the retry policy to invoke a method that may fail because of a transient fault.

using Microsoft.Practices.TransientFaultHandling;
using Microsoft.Practices.EnterpriseLibrary.WindowsAzure.TransientFaultHandling;
...
// Define your retry strategy: retry 5 times, starting 1 second apart
// and adding 2 seconds to the interval each retry.
var retryStrategy = new Incremental(5, TimeSpan.FromSeconds(1), 
  TimeSpan.FromSeconds(2));

// Define your retry policy using the retry strategy and the Azure storage
// transient fault detection strategy.
var retryPolicy =
  new RetryPolicy<StorageTransientErrorDetectionStrategy>(retryStrategy);

// Receive notifications about retries.
retryPolicy.Retrying += (sender, args) =>
    {
        // Log details of the retry.
        var msg = String.Format("Retry - Count:{0}, Delay:{1}, Exception:{2}",
            args.CurrentRetryCount, args.Delay, args.LastException);
        Trace.WriteLine(msg, "Information");
    };

try
{
  // Do some work that may result in a transient fault.
  retryPolicy.ExecuteAction(
    () =>
    {
        // Call a method that uses Azure storage and which may
        // throw a transient exception.
        this.queue.CreateIfNotExist();
    });
}
catch (Exception)
{
  // All the retries failed.
}

This example shows how to use the Retrying event to receive notifications in your code when a retry occurs.

Usage Notes

• The block provides three retry strategy classes: Incremental, FixedInterval, and ExponentialBackoff.
• The block provides overloaded versions of the Incremental, FixedInterval, and ExponentialBackoffconstructors that enable you to specify whether the first retry should be attempted immediately. The default behavior is that the first retry should happen immediately.
• The block provides four detection strategy classes: StorageTransientErrorDetectionStrategy, CacheTransientErrorDetectionStrategy, ServiceBusTransientErrorDetectionStrategy, and SqlAzureTransientErrorDetectionStrategy.
• Overloaded versions of the ExecuteAction method enable you to invoke methods that return void, that return a value, and that are either synchronous or asynchronous.
• If you are using Microsoft Azure storage and you have already defined a retry policy by using the Microsoft.WindowsAzure.StorageClient.RetryPolicy delegate, then you can use this policy with the block through the AzureStorageExtensions class and the AsAzureStorageClientRetryPolicy method.
• If you are re-using the same RetryPolicy instance in multiple locations in your code, be aware that the same Retrying event handler will be invoked from each location.

Next Topic | Previous Topic | Home

Last built: June 7, 2012