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C# | Check if ArrayList is Synchronized (thread safe)

Last Updated : 11 Jul, 2025
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ArrayList.IsSynchronized Property is used to get a value which indicate whether access to the ArrayList is synchronized (thread safe). Syntax: 
public virtual bool IsSynchronized { get; }
Return Value: This property returns the true if access to the ArrayList is synchronized (thread safe) otherwise it returns false. The default is false. Below programs illustrate the use of above-discussed property: Example 1: CSharp 
// C# code to check if ArrayList
// Is Synchronized or not
using System;
using System.Collections;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating an ArrayList
        ArrayList myList = new ArrayList();

        // Adding elements to ArrayList
        myList.Add("A");
        myList.Add("B");
        myList.Add("C");
        myList.Add("D");
        myList.Add("E");
        myList.Add("F");

        // Creates a synchronized
        // wrapper around the ArrayList
        ArrayList smyList = ArrayList.Synchronized(myList);

        // Displays the synchronization
        // status of both ArrayList
        Console.WriteLine("myList is {0}.", myList.IsSynchronized ?
                               "Synchronized" : "Not Synchronized");

        Console.WriteLine("smyList is {0}.", smyList.IsSynchronized ? 
                                "Synchronized" : "Not Synchronized");
    }
}
Output: 
myList is Not Synchronized.
smyList is Synchronized.
Example 2: CSharp 
// C# code to check if ArrayList
// Is Synchronized or not
using System;
using System.Collections;

class GFG {

    // Driver code
    public static void Main()
    {

        // Creating an ArrayList
        ArrayList myList = new ArrayList();

        // Adding elements to ArrayList
        myList.Add(1);
        myList.Add(2);
        myList.Add(3);
        myList.Add(4);
        myList.Add(5);
        myList.Add(5);

        // the default is false for 
        // IsSynchronized property
        Console.WriteLine(myList.IsSynchronized);
    }
}
Output: 
False
Note:
  • Retrieving the value of this property is an O(1) operation.
  • To guarantee the thread safety of the ArrayList, all operations must be done through the wrapper returned by the Synchronized method.
  • Enumerating through a collection is intrinsically not a thread-safe procedure. Even when a collection is synchronized, other threads can still modify the collection, which causes the enumerator to throw an exception.
Reference:

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Kirti_Mangal
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