Hashtable.Synchronized(Hashtable) Method

Definition

Namespace:

System.Collections

Assembly:

System.Runtime.dll

Source:

Hashtable.cs

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

public:
 static System::Collections::Hashtable ^ Synchronized(System::Collections::Hashtable ^ table);

public static System.Collections.Hashtable Synchronized (System.Collections.Hashtable table);

static member Synchronized : System.Collections.Hashtable -> System.Collections.Hashtable

Public Shared Function Synchronized (table As Hashtable) As Hashtable

Parameters

table

Hashtable

The Hashtable to synchronize.

Returns

Hashtable

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

Exceptions

ArgumentNullException

table is null.

Examples

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

#using <system.dll>

using namespace System;
using namespace System::Collections;
void main()
{
   
   // Creates and initializes a new Hashtable.
   Hashtable^ myHT = gcnew Hashtable;
   myHT->Add( (int^)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.
   Hashtable^ mySyncdHT = Hashtable::Synchronized( myHT );
   
   // Displays the sychronization status of both Hashtables.
   Console::WriteLine( "myHT is {0}.", myHT->IsSynchronized ? (String^)"synchronized" : "not synchronized" );
   Console::WriteLine( "mySyncdHT is {0}.", mySyncdHT->IsSynchronized ? (String^)"synchronized" : "not synchronized" );
}

/*
 This code produces the following output.

 myHT is not synchronized.
 mySyncdHT is synchronized.
 */

using System;
using System.Collections;

public class SamplesHashtable2
{
    public static void Main()
    {
        // Creates and initializes a new Hashtable.
        var myHT = 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.
        Hashtable mySyncdHT = Hashtable.Synchronized(myHT);

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

/*
This code produces the following output.

myHT is not synchronized.
mySyncdHT is synchronized.
*/

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, "synchronized", "not synchronized")
        Console.WriteLine($"myHT is {msg}.")
        msg = If(mySyncdHT.IsSynchronized, "synchronized", "not synchronized")
        Console.WriteLine($"mySyncdHT is {msg}.")
    End Sub
End Class

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

Remarks

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:

Hashtable^ myCollection = gcnew Hashtable();
bool lockTaken = false;

try
{
    Monitor::Enter(myCollection->SyncRoot, lockTaken);
    for each (Object^ item in myCollection)
    {
        // Insert your code here.
    }
}
finally
{
    if (lockTaken)
    {
        Monitor::Exit(myCollection->SyncRoot);
    }
}

var myCollection = new Hashtable();
lock (myCollection.SyncRoot)
{
    foreach (object item in myCollection)
    {
        // Insert your code here.
    }
}

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.

See also

• IsSynchronized
• SyncRoot