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Queue.Synchronized Method

Returns a new Queue that wraps the original queue, and is thread safe.

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

<HostProtectionAttribute(SecurityAction.LinkDemand, Synchronization := True)> _
Public Shared Function Synchronized ( _
	queue As Queue _
) As Queue


Type: System.Collections.Queue

The Queue to synchronize.

Return Value

Type: System.Collections.Queue
A Queue wrapper that is synchronized (thread safe).


queue is Nothing.

The wrapper returned by this method locks the queue before an operation is performed so that it is performed in a thread-safe manner.

To guarantee the thread safety of the Queue, all operations must be done through this wrapper only.

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 HostProtectionAttribute attribute applied to this type or member 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.

The following code example shows how to lock the collection using the SyncRoot during the entire enumeration. This method is an O(1) operation.

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

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

Imports System
Imports System.Collections

Public Class SamplesQueue    

    Public Shared Sub Main()

        ' Creates and initializes a new Queue. 
        Dim myQ As New Queue()

        ' Creates a synchronized wrapper around the Queue. 
        Dim mySyncdQ As Queue = Queue.Synchronized(myQ)

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

' This code produces the following output. 
' myQ is not synchronized. 
' mySyncdQ 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
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