Solve real coding problems
The simplest way to add or overwrite a value in a ConcurrentDictionary is to use the indexer: If the key doesn’t exist, this adds it. If the key exists, this overwrites it. The indexer is thread-safe. The indexer is the simplest way to unconditionally add / overwrite a value. Sometimes you’ll want to use other … Read more
Let’s say you’re firing off Task.Run() a bunch of times in a loop and passing in the loop variable, like this: The natural assumption is that this will print out 0 through 9. But instead, it’s printing out ten 10’s: This is a common mistake, especially when using Task.Run() in a loop. What’s happening here … Read more
When you want thread(s) to wait until they’re signaled before continuing, there are two simple options: I’ll show examples of using both of these. ManualResetEventSlim examples ManualResetEventSlim is like waving a flag at a car race. All race cars (threads) line up at the starting line and wait for the flag, and then they all … Read more
When a Task throws an exception and stops running, it has faulted. The question is, how do you get the exception that was thrown from the faulted Task? This depends on if you’re awaiting the Task or not. This article shows how to handle a faulted Task’s exception in two scenarios: when you’re awaiting the … Read more
The Async Main feature was added in C# 7.1 and works with all overloads of the Main() method. To make the Main() method async, add async Task to the method signature, like this: This is syntax sugar that compiles down to calling GetAwaiter().GetResult() on whatever you’re awaiting. In other words, it’s equivalent to doing the … Read more
The HttpClient class was designed to be used concurrently. It’s thread-safe and can handle multiple requests. You can fire off multiple requests from the same thread and await all of the responses, or fire off requests from multiple threads. No matter what the scenario, HttpClient was built to handle concurrent requests. To use HttpClient effectively … Read more
You can use the FileSystemWatcher class to detect file system changes, such as when a file is created, deleted, modified, or renamed. When a change happens, it raises an event that you can handle. This is an event-based alternative to polling for file changes. In this article, I’ll show how to use FileSystemWatcher to detect … Read more
Let’s say you have code that converts a string to a DateTime with DateTime.Parse(): By default, DateTime.Parse() uses CultureInfo.CurrentCulture to figure out the date format. The current culture ultimately comes from your OS settings. So when you run this code on a computer that is using the en-US locale, the current culture will automatically default … Read more
When you have multiple threads trying to do work at the same time, and you want to throttle how many of them are actually executing (such as when you’re sending concurrent requests with HttpClient), you can use SemaphoreSlim. Example – a busy grocery store Grocery stores have a limited number of checkout lanes open. Let’s … Read more
You can use SQL Server query notifications to send push notifications to your code when data changes. This is an alternative to polling the database for changes. In this article, I’ll show how to configure this feature and work with it in the code. 1 – Enable Service Broker and configure permissions You need to … Read more
One day I decided to challenge myself by trying to implement multithreaded quicksort. I wanted to see how it would compare to the built-in Array.Sort() method. I came up with two algorithms that were 2-4x faster than Array.Sort(): After continuing to tinker, in attempts to further optimize, I came across the AsParallel().OrderBy() method (PLINQ). After … Read more
I often need to be able to run multiple threads and update the UI based on the results. For example, I may need to execute GET requests to 10 different endpoints concurrently, and then report their results in a datagrid as they come back. The problem is you can’t just update the UI from any … Read more