This documentation is archived and is not being maintained.

ArrayList.Synchronized Method (ArrayList)

.NET Framework 1.1

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

[Visual Basic]
Overloads Public Shared Function Synchronized( _
   ByVal list As ArrayList _
) As ArrayList
[C#]
public static ArrayList Synchronized(
 ArrayList list
);
[C++]
public: static ArrayList* Synchronized(
 ArrayList* list
);
[JScript]
public static function Synchronized(
   list : ArrayList
) : ArrayList;

Parameters

list
The ArrayList to synchronize.

Return Value

An ArrayList wrapper that is synchronized (thread-safe).

Exceptions

Exception Type Condition
ArgumentNullException list is a null reference (Nothing in Visual Basic).

Remarks

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 could 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.

[Visual Basic, C#] The following code example shows how to lock the collection using the SyncRoot during the entire enumeration:

[C#] 
ArrayList myCollection = new ArrayList();
 lock( myCollection.SyncRoot ) {
 foreach ( Object item in myCollection ) {
 // Insert your code here.
 }
}
[Visual Basic] 
Dim myCollection As New ArrayList()
Dim item As Object
SyncLock myCollection.SyncRoot
 For Each item In myCollection
 ' Insert your code here.
 Next item
End SyncLock

Example

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

[Visual Basic] 
Imports System
Imports System.Collections

Public Class SamplesArrayList
    
    
    Public Shared Sub Main()
        
        ' Creates and initializes a new ArrayList.
        Dim myAL As New ArrayList()
        myAL.Add("The")
        myAL.Add("quick")
        myAL.Add("brown")
        myAL.Add("fox")
        
        ' Creates a synchronized wrapper around the ArrayList.
        Dim mySyncdAL As ArrayList = ArrayList.Synchronized(myAL)
        
        ' Displays the sychronization status of both ArrayLists.
        Dim str As String
        If myAL.IsSynchronized Then
            str = "synchronized"
        Else
            str = "not synchronized"
        End If
        Console.WriteLine("myAL is {0}.", str)
        If mySyncdAL.IsSynchronized Then
            str = "synchronized"
        Else
            str = "not synchronized"
        End If
        Console.WriteLine("mySyncdAL is {0}.", str)
    End Sub
End Class

' This code produces the following output.
' 
' myAL is not synchronized.
' mySyncdAL is synchronized. 

[C#] 
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.
*/ 

[C++] 
#using <mscorlib.dll>
using namespace System;
using namespace System::Collections;


int main()  {
 
       // Creates and initializes a new ArrayList instance.
       ArrayList* myAL = new ArrayList();
       myAL->Add( S"The" );
       myAL->Add( S"quick" );
       myAL->Add( S"brown" );
       myAL->Add( S"fox" );
 
       // Creates a synchronized wrapper around the ArrayList.
       ArrayList* mySyncdAL = ArrayList::Synchronized( myAL );
 
       // Displays the sychronization status of both ArrayLists.
       String* szRes = myAL->IsSynchronized ? "synchronized" : "not synchronized";
       Console::WriteLine( "myAL is {0}.", szRes );

       String* szSyncRes = mySyncdAL->IsSynchronized ? "synchronized" : "not synchronized";
       Console::WriteLine( "mySyncdAL is {0}.", szSyncRes );
    }

 /* 
 This code produces the following output.
 
 myAL is not synchronized.
 mySyncdAL is synchronized.
 */ 

[JScript] 
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.
 */ 

Requirements

Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family, .NET Compact Framework, Common Language Infrastructure (CLI) Standard

See Also

ArrayList Class | ArrayList Members | System.Collections Namespace | ArrayList.Synchronized Overload List | SyncRoot | IsSynchronized

Show: