Enter a Catch Method in WaitAndRetryAsync

user_484390 0
Viewed 180

Goal:
If you have tried the third time and it is not a success. Then you want to use another method.
I would like to to prevent displaying a error message webpage.

Problem:
is it possible to enter a method that is similiar as catch method in WaitAndRetryAsync?

RetryPolicy<HttpResponseMesssage> httpWaitAndRetryPolicy = Policy
    .HandleResult<HttpResponseMessage>(r => !r.IsSuccessStatusCode)
    .WaitAndRetryAsync
        (3, retryAttempt => TimeSpan.FromSeconds(Math.Pow(2. retryAttempt)/2));

Thank you!

asp.net-core-2.0 polly c#
2 Answers

You can use ExecuteAsync on your policy and then use ContinueWith to handle final response like this:

 RetryPolicy<HttpResponseMessage>
 .Handle<HttpRequestException>()
 .Or<TaskCanceledException>()
 .WaitAndRetryAsync
     (3, retryAttempt => TimeSpan.FromSeconds(Math.Pow(2, retryAttempt) / 2))
 .ExecuteAsync(() =>
 {
     //do stuff that you want retry

 }).ContinueWith(x =>
 {
     if (x.Exception != null)
     {
         //means exception raised during execute and handle it
     }

     // return your HttpResponseMessage
 }, scheduler: TaskScheduler.Default);

Following @TheodorZoulias's comment the best practice for use ContinueWith is to explicit set TaskScheduler to defualt, because ContinueWith change the scheduler to Current and maybe cause to deadlock.

user_60231730

First of all the WaitAndRetryAsync returns an AsyncRetryPolicy<T>, not a RetryPolicy<T>, which means that your posted code does not compile.

In case of polly the definition of a policy and the execution of that policy are separated. So, first you define a policy (or a mixture of policies) and then execute it whenever it is needed.

Definition

AsyncRetryPolicy<HttpResponseMessage> retryInCaseOfNotSuccessResponsePolicy = Policy
    .HandleResult<HttpResponseMessage>(r => !r.IsSuccessStatusCode)
    .WaitAndRetryAsync
        (3, retryAttempt => TimeSpan.FromSeconds(Math.Pow(2.retryAttempt) / 2));

Execution

HttpResponseMessage serviceResponse = null;
try
{
    serviceResponse = await retryInCaseOfNotSuccessResponsePolicy.ExecuteAsync(
        async ct => await httpClient.GetAsync(resourceUri, ct), default);
}
catch (Exception ex)
    when(ex is HttpRequestException || ex is OperationCanceledException)
{
    //TODO: log
}

if (serviceResponse == null)
{
    //TODO: log
}
user_132688550
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