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Hashtable.Synchronized Method

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

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

'Declaration
Public Shared Function Synchronized ( _
	table As Hashtable _
) As Hashtable
'Usage
Dim table As Hashtable
Dim returnValue As Hashtable

returnValue = Hashtable.Synchronized(table)
public static Hashtable Synchronized (
	Hashtable table
)
public static function Synchronized (
	table : Hashtable
) : Hashtable
Not applicable.

Parameters

table

The Hashtable to synchronize.

Return Value

A synchronized (thread safe) wrapper for the Hashtable.

Exception typeCondition

ArgumentNullException

table is a null reference (Nothing in Visual Basic).

NoteNote:

The HostProtectionAttribute attribute applied to this method 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.

Synchronized supports multiple writing threads, provided that no threads are reading the Hashtable. The synchronized wrapper does not provide thread-safe access in the case of one or more readers and one or more writers.

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

import System.*;
import System.Collections.*;

public class SamplesHashtable
{
    public static void main(String[] args)
    {
        // Creates and initializes a new Hashtable.
        Hashtable myHT = new Hashtable();

        myHT.Add(new Integer(0), "zero");
        myHT.Add(new Integer(1), "one");
        myHT.Add(new Integer(2), "two");
        myHT.Add(new Integer(3), "three");
        myHT.Add(new Integer(4), "four");

        // Creates a synchronized wrapper around the Hashtable.
        Hashtable mySyncdHT = Hashtable.Synchronized(myHT);

        // Displays the sychronization status of both Hashtables.
        Console.WriteLine("myHT is {0}.", (myHT.get_IsSynchronized()) ? 
            "synchronized" : "not synchronized");
        Console.WriteLine("mySyncdHT is {0}.", 
            (mySyncdHT.get_IsSynchronized()) ? 
            "synchronized" : "not synchronized");
    } //main
} //SamplesHashtable

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

import System
import System.Collections

// Creates and initializes a new Hashtable.
var myHT : Hashtable = 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.
var mySyncdHT : Hashtable = Hashtable.Synchronized(myHT)

// Displays the sychronization status of both Hashtables.
var msg : String
if(myHT.IsSynchronized)
    msg = "synchronized"
else
    msg = "not synchronized"
Console.WriteLine("myHT is {0}.", msg)
if(mySyncdHT.IsSynchronized)
    msg = "synchronized"
else
    msg = "not synchronized"
Console.WriteLine("mySyncdHT is {0}.", msg)

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

Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0, 1.0

XNA Framework

Supported in: 1.0

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