C# | Creating a synchronized (thread-safe) wrapper for the ArrayList

Synchronized(ArrayList) method is used to get an ArrayList wrapper that is synchronized (thread safe).

Syntax:

public static System.Collections.ArrayList Synchronized (System.Collections.ArrayList list);

Here, the list is the ArrayList which is to be synchronized.

Return Value: It returns an ArrayList wrapper which is synchronized (thread safe).

Exception: This method throws ArgumentNullException if the list is null.

Below programs illustrate the use of above-discussed method:

Example 1:

// 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("Geeks");
        myList.Add("for");
        myList.Add("Geeks");
        myList.Add("Noida");
        myList.Add("Geeks Classes");
        myList.Add("Delhi");

        // 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:

// 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("Geeks");
        myList.Add("for");
        myList.Add("Geeks");
        myList.Add("Noida");
        myList.Add("Geeks Classes");
        myList.Add("Delhi");

        // it will give error as
        // the parameter is null
        ArrayList smyList = ArrayList.Synchronized(null);
    }
}

Runtime Error:

Unhandled Exception:
System.ArgumentNullException: Value cannot be null.
Parameter name: list

Note: For the thread safety of the ArrayList, all operations must be done through this wrapper.

Reference:

• https://docs.microsoft.com/en-us/dotnet/api/system.collections.arraylist.synchronized?view=netframework-4.7.2#System_Collections_ArrayList_Synchronized_System_Collections_ArrayList_