How to Safely Cancel an Async Operation in C#

Asynchronous programming is essential for building responsive applications, but it comes with challenges - particularly when you need to cancel operations.

Here's how to safely implement cancellation in C#.

Using CancellationTokenSource

The key to proper cancellation is the CancellationTokenSource class. This provides a token that can be passed to async methods and monitored for cancellation requests.

// Create a cancellation source with timeout
var cts = new CancellationTokenSource(TimeSpan.FromSeconds(10));
var token = cts.Token;

try
{
    // Pass token to async operations
    await DoLongRunningTaskAsync(token);
}
catch (OperationCanceledException)
{
    // Handle cancellation gracefully
    Console.WriteLine("Operation was canceled");
}
finally
{
    // Always dispose the CancellationTokenSource
    cts.Dispose();
}

Implementing Cancellation in Your Methods

When writing cancellable async methods, check for cancellation at appropriate points:

async Task DoLongRunningTaskAsync(CancellationToken token)
{
    // Check before starting expensive work
    token.ThrowIfCancellationRequested();
    
    for (int i = 0; i < 100; i++)
    {
        // Periodically check during loops
        if (token.IsCancellationRequested)
        {
            // Clean up resources if needed
            CleanupResources();
            
            // Then throw the standard exception
            throw new OperationCanceledException(token);
        }
        
        await Task.Delay(100, token); // Built-in methods accept tokens
    }
}

Best Practices

  1. Always dispose of CancellationTokenSource objects
  2. Use token.ThrowIfCancellationRequested() for cleaner code
  3. Check for cancellation before expensive operations
  4. Pass the token to all nested async calls
  5. Handle OperationCanceledException appropriately in your calling code

By following these patterns, you can ensure your async operations respond promptly to cancellation requests while maintaining clean, resource-efficient code.

0
5

Related

XML (Extensible Markup Language) is a widely used format for storing and transporting data.

In C#, you can create XML files efficiently using the XmlWriter and XDocument classes. This guide covers both methods with practical examples.

Writing XML Using XmlWriter

XmlWriter provides a fast and memory-efficient way to generate XML files by writing elements sequentially.

Example:

using System;
using System.Xml;

class Program
{
    static void Main()
    {
        using (XmlWriter writer = XmlWriter.Create("person.xml"))
        {
            writer.WriteStartDocument();
            writer.WriteStartElement("Person");

            writer.WriteElementString("FirstName", "John");
            writer.WriteElementString("LastName", "Doe");
            writer.WriteElementString("Age", "30");

            writer.WriteEndElement();
            writer.WriteEndDocument();
        }
        Console.WriteLine("XML file created successfully.");
    }
}

Output (person.xml):

<?xml version="1.0" encoding="utf-8"?>
<Person>
    <FirstName>John</FirstName>
    <LastName>Doe</LastName>
    <Age>30</Age>
</Person>

Writing XML Using XDocument

The XDocument class from LINQ to XML provides a more readable and flexible way to create XML files.

Example:

using System;
using System.Xml.Linq;

class Program
{
    static void Main()
    {
        XDocument doc = new XDocument(
            new XElement("Person",
                new XElement("FirstName", "John"),
                new XElement("LastName", "Doe"),
                new XElement("Age", "30")
            )
        );
        doc.Save("person.xml");
        Console.WriteLine("XML file created successfully.");
    }
}

This approach is ideal for working with complex XML structures and integrating LINQ queries.

When to Use Each Method

  • Use XmlWriter when performance is critical and you need to write XML sequentially.
  • Use XDocument when you need a more readable, maintainable, and flexible way to manipulate XML.

Conclusion

Writing XML files in C# is straightforward with XmlWriter and XDocument. Choose the method that best suits your needs for performance, readability, and maintainability.

1
127

Raw string literals in C# provide a flexible way to work with multiline strings, with some interesting rules around how quotes work.

The key insight is that you can use any number of double quotes (three or more) to delimit your string, as long as the opening and closing sequences have the same number of quotes.

The Basic Rules

  1. You must use at least three double quotes (""") to start and end a raw string literal
  2. The opening and closing quotes must have the same count
  3. The closing quotes must be on their own line for proper indentation
  4. If your string content contains a sequence of double quotes, you need to use more quotes in your delimiter than the longest sequence in your content

Examples with Different Quote Counts

// Three quotes - most common usage
string basic = """
    This is a basic
    multiline string
    """;

// Four quotes - when your content has three quotes
string withThreeQuotes = """"
    Here's some text with """quoted""" content
    """";

// Five quotes - when your content has four quotes
string withFourQuotes = """""
    Here's text with """"nested"""" quotes
    """"";

// Six quotes - for even more complex scenarios
string withFiveQuotes = """"""
    Look at these """""nested""""" quotes!
    """""";

The N+1 Rule

The general rule is that if your string content contains N consecutive double quotes, you need to wrap the entire string with at least N+1 quotes. This ensures the compiler can properly distinguish between your content and the string's delimiters.

// Example demonstrating the N+1 rule
string example1 = """
    No quotes inside
    """; // 3 quotes is fine

string example2 = """"
    Contains """three quotes"""
    """"; // Needs 4 quotes (3+1)

string example3 = """""
    Has """"four quotes""""
    """""; // Needs 5 quotes (4+1)

Practical Tips

  • Start with three quotes (""") as your default
  • Only increase the quote count when you actually need to embed quote sequences in your content
  • The closing quotes must be on their own line and should line up with the indentation you want
  • Any whitespace to the left of the closing quotes defines the baseline indentation
// Indentation example
string properlyIndented = """
    {
        "property": "value",
        "nested": {
            "deeper": "content"
        }
    }
    """; // This line's position determines the indentation

This flexibility with quote counts makes raw string literals extremely versatile, especially when dealing with content that itself contains quotes, like JSON, XML, or other structured text formats.

1
71

Reading a file line by line is useful when handling large files without loading everything into memory at once.

✅ Best Practice: Use File.ReadLines() which is more memory efficient.

Example

foreach (string line in File.ReadLines("file.txt"))
{
    Console.WriteLine(line);
}

Why use ReadLines()?

Reads one line at a time, reducing overall memory usage. Ideal for large files (e.g., logs, CSVs).

Alternative: Use StreamReader (More Control)

For scenarios where you need custom processing while reading the contents of the file:

using (StreamReader reader = new StreamReader("file.txt"))
{
    string? line;
    while ((line = reader.ReadLine()) != null)
    {
        Console.WriteLine(line);
    }
}

Why use StreamReader?

Lets you handle exceptions, encoding, and buffering. Supports custom processing (e.g., search for a keyword while reading).

When to Use ReadAllLines()? If you need all lines at once, use:

string[] lines = File.ReadAllLines("file.txt");

Caution: Loads the entire file into memory—avoid for large files!

3
249