ConcurrentBag<T> in C#: Thread-Safe Collection Guide


In the world of concurrent programming in C#, managing data safely across multiple threads is a paramount concern. With the introduction of ConcurrentBag, the .NET framework offers a powerful tool for developers to handle collections concurrently without worrying about threading issues. In this article, we'll delve into ConcurrentBag and its usage and provide simple examples to help developers grasp its concepts more effectively.

Understanding ConcurrentBag

ConcurrentBag is a thread-safe collection class introduced in .NET Framework 4.0 under the System.Collections.Concurrent namespace. It is designed to store objects of type T in a thread-safe manner, making it suitable for scenarios where multiple threads need to add, remove, or iterate over items simultaneously.

Key Features

  1. Thread Safety: ConcurrentBag ensures thread safety by employing locking mechanisms internally. This means multiple threads can manipulate the bag concurrently without encountering race conditions or other synchronization issues.
  2. No Ordering Guarantee: Unlike some other concurrent collections like ConcurrentQueue or ConcurrentStack, ConcurrentBag does not guarantee the order of elements. It is primarily optimized for scenarios where order is not significant.
  3. Allows Duplicates: ConcurrentBag permits duplicate elements. Each addition operation adds the item to the bag without checking for duplicates. This behavior can be advantageous in certain scenarios where duplicates are acceptable.

Basic Usage Example

Let's walk through a simple example to illustrate how ConcurrentBag can be used in a multi-threaded environment:

using System;
using System.Collections.Concurrent;
using System.Threading.Tasks;

class Program
    static void Main(string[] args)
        ConcurrentBag<int> concurrentBag = new ConcurrentBag<int>();

        // Add items concurrently using Parallel.ForEach
        Parallel.ForEach(Enumerable.Range(1, 10), (i) =>
            Console.WriteLine($"Added {i} by Thread {Task.CurrentId}");

        // Iterate over the bag to print items
        Console.WriteLine("\nContents of ConcurrentBag:");
        foreach (var item in concurrentBag)

In this example, we create a ConcurrentBag and add integers from 1 to 10 concurrently using Parallel.ForEach. Each addition operation is executed by a different thread. Finally, we iterate over the bag to print its contents.


ConcurrentBag is a valuable addition to the .NET framework for handling concurrency scenarios efficiently. By providing thread-safe operations on collections, it simplifies development tasks related to multi-threaded programming, ensuring data integrity and preventing common synchronization issues.

Developers should leverage ConcurrentBag in scenarios where thread safety and concurrent access to a collection are required. However, it's essential to remember that while ConcurrentBag offers thread safety, it does not guarantee ordering or provide atomicity for compound operations. Understanding these nuances will help developers harness the full potential of ConcurrentBag in their applications.

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