Using Asynchronous Methods with Retries

You can use the Transient Fault Handling Application Block to invoke asynchronous methods that require a retry policy.

The following code example shows how to invoke the pair of asynchronous methods BeginDeleteIfExists and EndDeleteIfExists. The EndDeleteIfExists method returns a Boolean value to indicate whether the blob was deleted.

// 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");
    };

// Do some work that may result in a transient fault.
retryPolicy.ExecuteAction(
    ac =>
    {
        // Invoke the begin method of the asynchronous call.
        this.DataBlob.BeginDeleteIfExists(ac, null);
    },
    ar =>
    {
        // Invoke the end method of the asynchronous call.
        return this.DataBlob.EndDeleteIfExists(ar);
    },
    v =>
    {
        // Action to perform if the asynchronous operation
        // succeeded.
        if (v)
            {
                Trace.WriteLine("Blob deleted successfully", "Information");
            }
            else
            {
                Trace.WriteLine("The Blob was not deleted", "Information");
            }
    },
    e =>
    {
        // Action to perform if the asynchronous operation
        // failed after all the retries.
        var msg = String.Format("Delete blob failed: {0}", e.ToString());
        Trace.WriteLine(msg, "Error");
    });

Usage Notes

• There are two overloaded versions of the ExecuteAction method that you can use to invoke asynchronous methods. One invokes methods that do not have a return value and one invokes methods that do have a return value. If the asynchronous method returns a value, it is passed to the success handler.
• You could use the value that is passed to the success handler to begin another asynchronous operation. For example, if deleting the blob succeeded, begin a copy from blob operation.
• The success handler is called when the asynchronous operation succeeds. The failure handler is called if the asynchronous operation cannot be completed despite the retry attempts.

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Last built: June 7, 2012