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ArrayList.Synchronized Method (ArrayList)

Returns an ArrayList wrapper that is synchronized (thread safe).

Namespace: System.Collections
Assembly: mscorlib (in mscorlib.dll)

public static ArrayList Synchronized (
	ArrayList list
)
public static ArrayList Synchronized (
	ArrayList list
)
public static function Synchronized (
	list : ArrayList
) : ArrayList
Not applicable.

Parameters

list

The ArrayList to synchronize.

Return Value

An ArrayList wrapper that is synchronized (thread safe).

Exception typeCondition

ArgumentNullException

list is a null reference (Nothing in Visual Basic).

NoteNote:

The HostProtectionAttribute attribute applied to this method has the following Resources property value: Synchronization. The HostProtectionAttribute does not affect desktop applications, which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser. For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes.

To guarantee the thread safety of the ArrayList, all operations must be done through this wrapper.

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. To guarantee thread safety during enumeration, you can either lock the collection during the entire enumeration or catch the exceptions resulting from changes made by other threads.

The following code example shows how to lock the collection using the SyncRoot during the entire enumeration.

ArrayList myCollection = new ArrayList();
  lock(myCollection.SyncRoot) {
  foreach (Object item in myCollection) {
  // Insert your code here.
  }
 }

This method is an O(1) operation.

The following code example shows how to synchronize an ArrayList, determine if an ArrayList is synchronized and use a synchronized ArrayList.

using System;
using System.Collections;
public class SamplesArrayList  {

   public static void Main()  {

      // Creates and initializes a new ArrayList.
      ArrayList myAL = new ArrayList();
      myAL.Add( "The" );
      myAL.Add( "quick" );
      myAL.Add( "brown" );
      myAL.Add( "fox" );

      // Creates a synchronized wrapper around the ArrayList.
      ArrayList mySyncdAL = ArrayList.Synchronized( myAL );

      // Displays the sychronization status of both ArrayLists.
      Console.WriteLine( "myAL is {0}.", myAL.IsSynchronized ? "synchronized" : "not synchronized" );
      Console.WriteLine( "mySyncdAL is {0}.", mySyncdAL.IsSynchronized ? "synchronized" : "not synchronized" );
   }
}
/* 
This code produces the following output.

myAL is not synchronized.
mySyncdAL is synchronized.
*/ 

import System.*;
import System.Collections.*;

public class SamplesArrayList
{
    public static void main(String[] args)
    {
        // Creates and initializes a new ArrayList.
        ArrayList myAL = new ArrayList();

        myAL.Add("The");
        myAL.Add("quick");
        myAL.Add("brown");
        myAL.Add("fox");

        // Creates a synchronized wrapper around the ArrayList.
        ArrayList mySyncdAL = ArrayList.Synchronized(myAL);

        // Displays the sychronization status of both ArrayLists.
        Console.WriteLine("myAL is {0}.", myAL.get_IsSynchronized()
            ? "synchronized" : "not synchronized");
        Console.WriteLine("mySyncdAL is {0}.", mySyncdAL.get_IsSynchronized()
            ? "synchronized" : "not synchronized");
    } //main
} //SamplesArrayList
/* 
 This code produces the following output.
 
 myAL is not synchronized.
 mySyncdAL is synchronized.
 */

import System;
import System.Collections;

// Creates and initializes a new ArrayList.
var myAL : ArrayList = new ArrayList();
myAL.Add( "The" );
myAL.Add( "quick" );
myAL.Add( "brown" );
myAL.Add( "fox" );

// Creates a synchronized wrapper around the ArrayList.
var mySyncdAL : ArrayList  = ArrayList.Synchronized( myAL );

// Displays the sychronization status of both ArrayLists.
Console.WriteLine( "myAL is {0}.", myAL.IsSynchronized ? "synchronized" : "not synchronized" );
Console.WriteLine( "mySyncdAL is {0}.", mySyncdAL.IsSynchronized ? "synchronized" : "not synchronized" );
 
 /* 
 This code produces the following output.
 
 myAL is not synchronized.
 mySyncdAL is synchronized.
 */ 

Windows 98, Windows Server 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

XNA Framework

Supported in: 1.0

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