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Synchronous & Asynchronous and MultiThread Programming -7 — Thread Local Storage & Timers

Alperen Öz
6 min readSep 7, 2024

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Thread Local Storage (TLS) & Timers

Thread Local Storage (TLS) in .NET

Thread Local Storage (TLS) is a mechanism in C# and other programming languages that allows each thread to maintain its own private storage for data. This is particularly useful in multi-threaded applications, where threads need to operate independently without interfering with each other’s data. TLS ensures that each thread can store its unique values, inaccessible by other threads, thus preserving thread data integrity.

Purpose and Advantages of Thread Local Storage

Purpose:

  1. The primary purpose of TLS is to provide a way for each thread to store data specific to its context. With TLS, every thread can maintain private data that cannot be accessed by any other thread, ensuring thread isolation and preventing conflicts that might arise in shared data access scenarios.

Advantages:

  1. Data Integrity: TLS ensures that data remains consistent and secure within a thread. If one thread modifies its stored value, this change applies solely to that thread, without affecting the data of other threads. This reduces the risk of data corruption and race conditions in multi-threaded environments.
  2. Performance: TLS can improve performance, particularly in scenarios where shared data access is frequent. By isolating data at the thread level, TLS eliminates the need for costly synchronization mechanisms, such as locks, thus reducing overhead and increasing efficiency.
  3. Code Maintainability and Safety: TLS promotes better code structure by reducing the complexity of managing shared data across threads. Each thread handles its own data, reducing potential bugs and making the codebase easier to maintain. Furthermore, by eliminating unsafe data sharing, the overall security and stability of the application are enhanced.

ThreadStatic Attribute

The ThreadStatic attribute in C# is used to indicate that a field or variable should have a separate instance for each thread.

When applied, each thread maintains its own copy of the value, which cannot be accessed or modified by other threads. This attribute is only applicable to static fields and ensures that a static field behaves as thread-specific data.

By using the ThreadStatic attribute, static variables are isolated per thread, allowing for the safe handling of thread-local data without needing additional synchronization mechanisms.

[ThreadStatic]
static int x = 0;
private static void Main(string[] args)
{
    Thread thread1 = new(() =>
    {
        while (x < 10)
            Console.WriteLine($"Thread1 {++x}");
    });

    Thread thread2 = new(() =>
    {
        while (x < 10)
            Console.WriteLine($"Thread2 {++x}");
    });

    Thread thread3 = new(() =>
    {
        while (x < 10)
            Console.WriteLine($"Thread3 {++x}");
    });

    thread1.Start();
    thread2.Start();
    thread3.Start();
}

//output without ThreadStatic attribute;

//Thread1 1
//Thread1 4
//Thread1 5
//Thread1 6
//Thread1 7
//Thread2 2
//Thread2 9
//Thread2 10
//Thread3 3
//Thread1 8

//output with ThreadStatic attribute;

//Thread2 1
//Thread1 1
//Thread3 1
//Thread3 2
//Thread1 2
//Thread1 3
//Thread1 4
//Thread3 3
//Thread3 4
//Thread3 5
//Thread3 6
//Thread1 5
//Thread2 2
//Thread2 3
//Thread1 6
//Thread1 7
//Thread1 8
//Thread1 9
//Thread1 10
//Thread3 7
//Thread3 8
//Thread2 4
//Thread3 9
//Thread2 5
//Thread2 6
//Thread2 7
//Thread2 8
//Thread2 9
//Thread2 10
//Thread3 10

As seen in the example, the variable x is marked with the ThreadStatic attribute. As a result, although thread1, thread2, and thread3 all use this shared variable, each of them creates its own instance of the x object in its local storage due to the ThreadStatic marking. Each thread, therefore, processes the x object independently within its own context.

In modern C# programming, the more powerful and flexible ThreadLocal<T> class is often preferred over the ThreadStatic attribute. This class provides similar functionality but with enhanced flexibility and safety.

ThreadLocal<T> Class

The ThreadLocal<T> class exhibits more flexible behavior compared to the ThreadStatic attribute by providing Thread-Local Storage (TLS) for both static and instance fields. This means that not only can static fields have thread-local data, but instance fields can also maintain separate data per thread.

Additionally, the ThreadLocal<T> class allows defining default values for the thread-local data. This adds further flexibility, as each thread can initialize its data with a specific value when the thread first accesses the ThreadLocal<T> instance.

ThreadLocal<int> x = new(() => 0);
Thread thread1 = new(() =>
{
    while (x.Value < 10)
        Console.WriteLine($"Thread1 {++x.Value}");
});

Thread thread2 = new(() =>
{
    while (x.Value < 10)
        Console.WriteLine($"Thread2 {++x.Value}");
});

Thread thread3 = new(() =>
{
    while (x.Value < 10)
        Console.WriteLine($"Thread3 {++x.Value}");
});

thread1.Start();
thread2.Start();
thread3.Start();

//Thread1 1
//Thread2 1
//Thread2 2
//Thread1 2
//Thread1 3
//Thread1 4
//Thread1 5
//Thread1 6
//Thread1 7
//Thread1 8
//Thread1 9
//Thread1 10
//Thread3 1
//Thread3 2
//Thread2 3
//Thread2 4
//Thread2 5
//Thread2 6
//Thread2 7
//Thread2 8
//Thread2 9
//Thread3 3
//Thread2 10
//Thread3 4
//Thread3 5
//Thread3 6
//Thread3 7
//Thread3 8
//Thread3 9
//Thread3 10

GetData & SetData Methods

Another approach to implementing Thread Local Storage (TLS) is through the use of the GetData and SetData methods. These methods store and retrieve data in areas specific to each thread, known as "slots."

Each slot is defined using the LocalDataStoreSlot object.

By using these methods, you can assign specific values to a thread’s unique slot, which helps in managing thread-specific data more effectively. These slots allow data isolation across threads, ensuring that each thread’s data remains independent.

static LocalDataStoreSlot localDataStoreSlot = Thread.GetNamedDataSlot("x");
    static int X
    {
        get
        {
            var data = (int?)Thread.GetData(localDataStoreSlot);
            return data is null ? 0 : data.Value;
        }
        set => Thread.SetData(localDataStoreSlot, value);
    }

    static void Main(string[] args)
    {
        Thread thread1 = new(() =>
        {
            while (X < 10)
                Console.WriteLine($"Thread1 {++X}");
        });

        Thread thread2 = new(() =>
        {
            while (X < 10)
                Console.WriteLine($"Thread2 {++X}");
        });

        Thread thread3 = new(() =>
        {
            while (X < 10)
                Console.WriteLine($"Thread3 {++X}");
        });

        thread1.Start();
        thread2.Start();
        thread3.Start();
    }

Timer Class

What are Timers?
Timers are tools used to schedule tasks that repeat at specific intervals. They are frequently used in software development to automate periodic tasks.

For example, timers can be used for regular data backups, sending scheduled notifications, or performing routine system maintenance tasks.

The .NET framework offers various timer classes customized for different needs. These timers are optimized for various scenarios and usage cases. They can be broadly categorized into two types: Multi-threaded Timers and Single-threaded Timers. These categories refer to the threads on which the timers operate and how they are used.

Timer Types in .NET Framework
The .NET framework provides several timer classes for different scenarios, including:

  • System.Threading.Timer
  • System.Timers.Timer
  • System.Windows.Forms.Timer
  • System.Windows.Threading.DispatcherTimer

These timers are designed to support both multi-threading and single-threading operations.

Multi-threaded Timers
Multi-threaded timers allow multiple threads to operate simultaneously and manage synchronization between these threads. They are ideal for background operations that are independent of UI updates.

System.Threading.Timer
System.Threading.Timer is a simple timer used for background tasks that need to run at specific intervals. This timer uses the Thread Pool to execute tasks, making it efficient in terms of performance.

Example Usage:

using System;
using System.Threading;

class Program
{
    static void Main()
    {
        Timer timer = new Timer(Callback, null, 0, 2000);
        Console.WriteLine("Press Enter to exit...");
        Console.ReadLine();
    }

    private static void Callback(object state)
    {
        Console.WriteLine("Tick: {0}", DateTime.Now);
    }
}

System.Timers.Timer
System.Timers.Timer wraps the System.Threading.Timer class and provides additional features.

It is specifically designed to handle timer events directly and offers more comprehensive event-driven programming capabilities.

Example Usage:

using System;
using System.Timers;

class Program
{
    static void Main()
    {
        Timer timer = new Timer(2000); // 2 seconds interval
        timer.Elapsed += OnTimedEvent;
        timer.AutoReset = true;
        timer.Enabled = true;

        Console.WriteLine("Press Enter to exit...");
        Console.ReadLine();
    }

    private static void OnTimedEvent(Object source, ElapsedEventArgs e)
    {
        Console.WriteLine("Tick: {0}", e.SignalTime);
    }
}

Single-threaded Timers
Single-threaded timers are typically used in UI applications and operate on a single thread. This is especially suitable for scenarios where user interface elements need to be updated. The System.Windows.Forms.Timer and System.Windows.Threading.DispatcherTimer are examples of single-threaded timer classes.

System.Windows.Forms.Timer
System.Windows.Forms.Timer is a timer class specifically designed for Windows Forms applications. It runs on the UI thread and can directly update user interface elements.

System.Windows.Threading.DispatcherTimer
System.Windows.Threading.DispatcherTimer is a timer class used in WPF applications. It operates on the Dispatcher thread and can interact with WPF user interface elements.

System.Threading and System.Timers Namespaces

  • System.Threading: The System.Threading namespace provides fundamental threading operations and synchronization objects. System.Threading.Timer is located within this namespace and is used for simple timer operations.
  • System.Timers: The System.Timers namespace supports event-based timers and wraps the System.Threading.Timer class. It provides additional features and convenience. System.Timers.Timer is found in this namespace and is used for more comprehensive timer operations.

Source: Gençay Yıldız — Asenkron & Multithread Programlama

Thread Local Storage
Multithreading

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Alperen Öz

Written by Alperen Öz

47 Followers

Software Engineer @SmartPulse

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