Blog
Mert Özen's blog posts on software development, backend, frontend, and DevOps.
Exceptions in C# Async: AggregateException and Errors in WhenAll
An exception in an async method goes into the task and is thrown with its original type at the await. Throwing parameter checks at the call, the difference between Wait, GetResult and await, reaching every error and partial results from WhenAll, an error order that differs between two overloads, AggregateException.Handle and unobserved task exceptions.
How C# async/await Works: The State Machine and Continuations
await does not always wait: on a finished task the code continues on the same thread. What the async keyword actually does, the GetAwaiter/IsCompleted/OnCompleted steps, a working hand-written state machine, looking at the compiler-generated type with reflection (a class in Debug, a struct in Release), which thread runs the continuation, and the awaitable pattern.
C# Task and Task<T>: A Promise That Starts Hot
An async method starts running the moment it is called; await does not start work, it waits for its result. The task life cycle and Status values, creating tasks with Task.FromResult and TaskCompletionSource, awaiting the same task twice, starting work first and awaiting later, and the Task<Task> trap of Task.Factory.StartNew.
C# Threads and the ThreadPool: A Short History of Async from APM and EAP to TPL
Foreground versus background threads, why the Thread class cannot carry results or errors, and a real measurement of 1000 threads against the thread pool. Then .NET's road to async: APM's Begin/End pair, EAP's Completed event, TPL's Task and the async/await that arrived with C# 5.
Why Async Exists in C#: Blocking, I/O and Scale
The same 100 stock queries finish in one second with async and in 8-9 seconds with code that blocks the thread. The difference between I/O-bound and CPU-bound work, what blocking costs in a UI and on a server, thread pool starvation, why async buys capacity rather than speed, and the fake async trap.
Async and Connection Management in Dapper: CancellationToken, Pooling and DI
We see with real output why a CancellationToken only travels through CommandDefinition in Dapper, why async on SQLite actually runs synchronously, how connection pooling helps, why sharing one connection breaks, and the connection factory pattern in ASP.NET Core.
Advanced JavaScript Async Patterns: The Promise.all Family, Cancellation, Retry and Timeouts
We look at the differences between Promise.all, allSettled, any and race, ES2024's Promise.withResolvers, ES2025's Promise.try, supporting AbortSignal in your own functions, retry, timeouts and concurrency limits.