C# : Polly Doesn't Work If Function Wraps Up With Try Catch

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Introduction

When working with databases, it's not uncommon to encounter connection timeouts or other exceptions that can disrupt the flow of our application. To mitigate these issues, we can use Polly, a popular .NET library for implementing retry logic and circuit breakers. However, in certain situations, Polly may not work as expected, especially when our code wraps up with a try-catch block. In this article, we'll explore this issue and provide a solution to get Polly working correctly.

Understanding Polly

Polly is a .NET library that provides a simple and flexible way to implement retry logic and circuit breakers. It allows us to define policies that can be applied to our code to handle exceptions and timeouts. With Polly, we can specify the number of retries, the delay between retries, and even the maximum number of attempts before giving up.

The Problem with Try-Catch Blocks

When we wrap our code with a try-catch block, Polly may not work as expected. This is because the try-catch block will catch the exception and execute the catch block directly, bypassing the Polly policy. As a result, the retry logic defined in Polly will not be executed.

Example Code

Let's consider an example code snippet that demonstrates this issue:

using Polly;
using System;
using System.Data.SqlClient;

class Program
{
static void Main(string[] args)
{
var policy = Policy.Handle<SqlException>()
.WaitAndRetry(3, retryAttempt => TimeSpan.FromSeconds(retryAttempt));


    using (var connection = new SqlConnection(&quot;Data Source=myServer;Initial Catalog=myDatabase;Integrated Security=True&quot;))
    {
        connection.Open();

        using (var command = new SqlCommand(&quot;SELECT * FROM myTable&quot;, connection))
        {
            try
            {
                command.ExecuteNonQuery();
            }
            catch (SqlException ex)
            {
                Console.WriteLine({{content}}amp;quot;Caught exception: {ex.Message}&quot;);
            }
        }
    }
}



}

In this example, we define a Polly policy that will retry the connection up to 3 times with a delay of 1 second between retries. However, when the SqlException is caught in the try-catch block, the Polly policy is not executed, and the retry logic is bypassed.

Solution

To get Polly working correctly, we need to remove the try-catch block and let Polly handle the exceptions. We can do this by using the Policy.Handle method to specify the exception type and the retry policy. Here's the updated code:

using Polly;
using System;
using System.Data.SqlClient;

class Program
{
static void Main(string[] args)
{
var policy = Policy.Handle<SqlException>()
.WaitAndRetry(3, retryAttempt => TimeSpan.FromSeconds(retryAttempt));


    using (var connection = new SqlConnection(&quot;Data Source=myServer;Initial Catalog=myDatabase;Integrated Security=True&quot;))
    {
        policy.Execute(() =&gt;
        {
            connection.Open();
            using (var command = new SqlCommand(&quot;SELECT * FROM myTable&quot;, connection))
            {
                command.ExecuteNonQuery();
            }
        });
    }
}



}

In this updated code, we use the Policy.Execute method to execute the code block within the Polly policy. If an exception occurs, Polly will catch it and retry the code block up to the specified number of times.

Best Practices

To ensure that Polly works correctly, follow these best practices:

  1. Remove try-catch blocks: Let Polly handle exceptions and retries.
  2. Use Policy.Handle: Specify the exception type and retry policy using Policy.Handle.
  3. Use Policy.Execute: Execute the code block within the Polly policy using Policy.Execute.

By following these best practices, you can ensure that Polly works correctly and provides the desired retry logic and circuit breaker behavior for your .NET applications.

Conclusion

Q&A: Troubleshooting Polly Issues

In the previous article, we explored the issue of Polly not working correctly when code wraps up with a try-catch block. In this article, we'll provide a Q&A section to help you troubleshoot common issues with Polly.

Q: Why is Polly not retrying my code?

A: There could be several reasons why Polly is not retrying your code. Here are a few possible causes:

  • Try-catch block: If you have a try-catch block in your code, Polly may not be able to catch the exception and retry the code.
  • Policy not defined: Make sure that you have defined a Polly policy using the Policy.Handle method.
  • Policy not executed: Ensure that you are executing the Polly policy using the Policy.Execute method.

Q: How do I configure Polly to retry my code?

A: To configure Polly to retry your code, you can use the Policy.Handle method to specify the exception type and the retry policy. Here's an example:

var policy = Policy.Handle<SqlException>()
    .WaitAndRetry(3, retryAttempt => TimeSpan.FromSeconds(retryAttempt));

In this example, we define a Polly policy that will retry the code up to 3 times with a delay of 1 second between retries.

Q: What is the difference between Policy.Handle and Policy.Execute?

A: Policy.Handle is used to specify the exception type and the retry policy, while Policy.Execute is used to execute the code block within the Polly policy. Here's an example:

var policy = Policy.Handle<SqlException>()
    .WaitAndRetry(3, retryAttempt => TimeSpan.FromSeconds(retryAttempt));

policy.Execute(() =>
{
// Code to be executed within the Polly policy
});

In this example, we define a Polly policy using Policy.Handle and then execute the code block within the policy using Policy.Execute.

Q: How do I handle multiple exceptions with Polly?

A: To handle multiple exceptions with Polly, you can use the Policy.Handle method to specify multiple exception types. Here's an example:

var policy = Policy.Handle<SqlException>()
    .Or<IOException>()
    .WaitAndRetry(3, retryAttempt => TimeSpan.FromSeconds(retryAttempt));

In this example, we define a Polly policy that will retry the code up to 3 times with a delay of 1 second between retries if either a SqlException or an IOException occurs.

Q: Can I use Polly with async code?

A: Yes, you can use Polly with async code. To do this, you can use the Policy.Handle method to specify the exception type and the retry policy, and then use the Policy.ExecuteAsync method to execute the async code block within the Polly policy. Here's an example:

var policy = Policy.Handle<SqlException>()
    .WaitAndRetry(3, retryAttempt => TimeSpan.FromSeconds(retryAttempt));

policy.ExecuteAsync(async () =>
{
// Async code to be executed within the Polly policy
});

In this example, we define a Polly policy using Policy.Handle and then execute the async code block within the policy using Policy.ExecuteAsync.

Conclusion

In this article, we provided a Q&A section to help you troubleshoot common issues with Polly. We covered topics such as configuring Polly to retry code, handling multiple exceptions, and using Polly with async code. By following these best practices, you can ensure that Polly provides the desired retry logic and circuit breaker behavior for your .NET applications.

Best Practices

To ensure that Polly works correctly, follow these best practices:

  1. Remove try-catch blocks: Let Polly handle exceptions and retries.
  2. Use Policy.Handle: Specify the exception type and retry policy using Policy.Handle.
  3. Use Policy.Execute: Execute the code block within the Polly policy using Policy.Execute.
  4. Use Policy.ExecuteAsync: Execute the async code block within the Polly policy using Policy.ExecuteAsync.
  5. Configure Polly correctly: Ensure that you have defined a Polly policy using the Policy.Handle method and executed the code block within the policy using Policy.Execute or Policy.ExecuteAsync.