Hashtable.Synchronized Method (Hashtable)

 

Returns a synchronized (thread-safe) wrapper for the Hashtable.

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

<HostProtectionAttribute(SecurityAction.LinkDemand, Synchronization := True)>
Public Shared Function Synchronized (
	table As Hashtable
) As Hashtable

Parameters

table
Type: System.Collections.Hashtable

The Hashtable to synchronize.

Return Value

Type: System.Collections.Hashtable

A synchronized (thread-safe) wrapper for the Hashtable.

Exception Condition
ArgumentNullException

table is null.

The Synchronized method is thread safe for multiple readers and writers. Furthermore, the synchronized wrapper ensures that there is only one writer writing at a time.

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.
    Next
End SyncLock

This method is an O(1) operation.

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"
        Else
            msg = "not synchronized"
        End If
        Console.WriteLine("myHT is {0}.", msg)
        If mySyncdHT.IsSynchronized Then
            msg = "synchronized"
        Else
            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. 

Universal Windows Platform
Available since 10
.NET Framework
Available since 1.1
Return to top
Show: