01-thread-vs-task.md

01 - Thread vs Task

Goal

Understand the difference between:

• sequential execution
• raw Thread
• Task
• Task.WhenAll

Step 1: Inspect the interface

public interface IActionRunner
{
    Task RunAsync(
        IReadOnlyCollection<Func<CancellationToken, Task>> actions,
        CancellationToken cancellationToken);
}

Step 2: Implement sequential execution

Open:

src/MultithreadingLab.Core/ActionRunners/SequentialActionRunner.cs

This version should execute one action after another.

Step 3: Implement raw Thread execution

Open:

src/MultithreadingLab.Core/ActionRunners/ThreadActionRunner.cs

Requirements:

• Create one Thread per action.
• Start each thread.
• Join each thread.
• Capture exceptions.
• Throw an AggregateException if any action fails.

Step 4: Implement Task-based execution

Open:

src/MultithreadingLab.Core/ActionRunners/TaskActionRunner.cs

Requirements:

• Schedule actions using Task.Run.
• Await all using Task.WhenAll.
• Respect cancellation.
• Do not swallow exceptions.

Step 5: Add tests

Create tests for:

• empty input
• all actions executed
• exception propagation
• cancellation behavior

Step 6: Benchmark

Run:

dotnet run -c Release --project benchmarks/MultithreadingLab.Benchmarks --filter *ActionRunner*

Compare:

• sequential
• raw thread
• task-based

Trade-offs

Raw Thread

Pros:

• Full control over thread lifetime.
• Good for understanding low-level behavior.

Cons:

• Expensive to create.
• Poor scalability when creating many threads.
• Easy to misuse with async code.

Task

Pros:

• Better default abstraction.
• Uses ThreadPool for CPU-bound work.
• Composes naturally with async/await.

Cons:

• Can still cause ThreadPool starvation if abused.
• Task.Run should not be used blindly around already-async I/O operations.

Key takeaway

Use raw Thread for learning or special low-level scenarios. Use Task, async/await, and higher-level primitives for most application code.