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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)

[HostProtectionAttribute(SecurityAction.LinkDemand, Synchronization = true)]
public static ArrayList Synchronized(
	ArrayList list
)

Parameters

list
Type: System.Collections.ArrayList
The ArrayList to synchronize.

Return Value

Type: System.Collections.ArrayList
An ArrayList wrapper that is synchronized (thread safe).

ExceptionCondition
ArgumentNullException

list is null.

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.

NoteNote

The HostProtectionAttribute attribute applied to this type or member 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.

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.
*/ 


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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