6. Task, Auto Reset Event

Task and AutoResetEvent in C#

Introduction

The C# language provides various ways to handle multithreaded programming, two of which include the Task class and the AutoResetEvent class.

AutoResetEvent

The AutoResetEvent class in C# is a signalling mechanism. It plays a vital role in thread synchronization, allowing one thread to unblock another. This class is found within the System.Threading namespace.

Key Points:

• An AutoResetEvent is used to send a signal to a thread that something happened.

• It has two primary states: signaled and non-signaled.

• When in the signaled state, if a thread calls WaitOne, the thread continues execution and the AutoResetEvent returns to the non-signaled state.

• If a thread calls WaitOne while the AutoResetEvent is in the non-signaled state, the thread will block until another thread changes the state to signaled using the Set method.

Example:

AutoResetEvent autoResetEvent = new AutoResetEvent(false);

Thread thread1 = new Thread(() => {
    Console.WriteLine("Thread1 is waiting...");
    autoResetEvent.WaitOne();
    Console.WriteLine("Thread1 is released...");
});

Thread thread2 = new Thread(() => {
    Console.WriteLine("Thread2 is working...");
    Thread.Sleep(2000); // simulates work
    autoResetEvent.Set();
    Console.WriteLine("Thread2 has signaled.");
});

thread1.Start();
thread2.Start();

Task Class

The Task class represents a single operation that does not return a value and that usually executes asynchronously. The Task class is a part of the System.Threading.Tasks namespace.

Key Points:

• The Task class leverages the thread pool to execute tasks in the background.

• Unlike a thread, a Task can return a result.

• A Task can be awaited, meaning it can be paused until the result is ready.

• The TaskCreationOptions enumeration provides several options for customizing the behavior of a task.

TaskCreationOptions

TaskCreationOptions is an enumeration that provides several options to customize the behavior of Task. The LongRunning option indicates that the task will take a long time to execute.

Example:

var task = Task.Factory.StartNew(() => TaskMethod("Task 1"), TaskCreationOptions.LongRunning);

Await vs Result

The key difference between await and Result is that Result blocks the current thread until the task is finished executing, while await does not block the current thread but instead yields control back to the caller until the task is completed.

Example:

public async Task<int> CalculateResult()
{
    await Task.Delay(5000); // simulates some calculation
    return 5;
}

public async Task TestMethod()
{
    Task<int> calculation = CalculateResult();
    int result = await calculation; // does not block the thread
    Console.WriteLine(result);
}

public void BlockingMethod()
{
    Task<int> calculation = CalculateResult();
    int result = calculation.Result; // blocks the thread
    Console.WriteLine(result);
}

In conclusion, understanding the Task and AutoResetEvent classes in C# is crucial for effective multithreaded programming. These classes provide the tools needed to create responsive applications that can handle a multitude of tasks simultaneously.

Reference

The content in this document is based on the original notes provided in Azerbaijani. For further details, you can refer to the original document using the following link:

Original Note - Azerbaijani Version