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IsSynchronized Property

Hashtable.IsSynchronized Property

Gets a value indicating whether access to the Hashtable 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 Hashtable is synchronized (thread safe); otherwise, false. The default is false.



A Hashtable can support one writer and multiple readers concurrently. To support multiple writers, 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 Hashtable()
SyncLock myCollection.SyncRoot
    For Each item In myCollection
        ' Insert your code here. 
End SyncLock

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

Imports System
Imports System.Collections

Public Class SamplesHashtable    

    Public Shared Sub Main()

        ' Creates and initializes a new Hashtable. 
        Dim myHT As New Hashtable()
        myHT.Add(0, "zero")
        myHT.Add(1, "one")
        myHT.Add(2, "two")
        myHT.Add(3, "three")
        myHT.Add(4, "four")

        ' Creates a synchronized wrapper around the Hashtable. 
        Dim mySyncdHT As Hashtable = Hashtable.Synchronized(myHT)

        ' Displays the sychronization status of both Hashtables. 
        Dim msg As String 
        If myHT.IsSynchronized Then
            msg = "synchronized" 
            msg = "not synchronized" 
        End If
        Console.WriteLine("myHT is {0}.", msg)
        If mySyncdHT.IsSynchronized Then
            msg = "synchronized" 
            msg = "not synchronized" 
        End If        
        Console.WriteLine("mySyncdHT is {0}.", msg)
    End Sub 
End Class 

' This code produces the following output. 
' myHT is not synchronized. 
' mySyncdHT is synchronized. 

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

XNA Framework

Supported in: 3.0, 2.0, 1.0
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