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ArrayList.IsSynchronized Property

Gets a value indicating whether access to the ArrayList is synchronized (thread safe).

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

Public Overridable ReadOnly Property IsSynchronized As Boolean

Property Value

Type: System.Boolean
true if access to the ArrayList is synchronized (thread safe); otherwise, false. The default is false.



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. 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.

Dim myCollection As New ArrayList()

SyncLock myCollection.SyncRoot
    For Each item As Object In myCollection
        ' Insert your code here.
    Next item
End SyncLock

Retrieving the value of this property 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.

Imports System
Imports System.Collections

Public Class SamplesArrayList

    Public Shared Sub Main()

        ' Creates and initializes a new ArrayList.
        Dim myAL As New ArrayList()

        ' 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"
            str = "not synchronized"
        End If
        Console.WriteLine("myAL is {0}.", str)
        If mySyncdAL.IsSynchronized Then
            str = "synchronized"
            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. 

.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.