Queue Class

Queues are useful for storing messages in the order they were received for sequential processing. This class implements a queue as a circular array. Objects stored in a Queue are inserted at one end and removed from the other.

The capacity of a Queue is the number of elements the Queue can hold. As elements are added to a Queue, the capacity is automatically increased as required through reallocation. The capacity can be decreased by calling TrimToSize.

The growth factor is the number by which the current capacity is multiplied when a greater capacity is required. The growth factor is determined when the Queue is constructed. The default growth factor is 2.0. The capacity of the Queue will always increase by at least a minimum of four, regardless of the growth factor. For example, a Queue with a growth factor of 1.0 will always increase in capacity by four when a greater capacity is required.

Queue accepts null as a valid value and allows duplicate elements.

For the generic version of this collection, see System.Collections.Generic.Queue<T>

The following example shows how to create and add values to a Queue and how to print out its values.

 using System;
 using System.Collections;
 public class SamplesQueue  {

    public static void Main()  {

       // Creates and initializes a new Queue.
       Queue myQ = new Queue();
       myQ.Enqueue("Hello");
       myQ.Enqueue("World");
       myQ.Enqueue("!");

       // Displays the properties and values of the Queue.
       Console.WriteLine( "myQ" );
       Console.WriteLine( "\tCount:    {0}", myQ.Count );
       Console.Write( "\tValues:" );
       PrintValues( myQ );
    }


    public static void PrintValues( IEnumerable myCollection )  {
       foreach ( Object obj in myCollection )
          Console.Write( "    {0}", obj );
       Console.WriteLine();
    }
 }
 /* 
 This code produces the following output.

 myQ
     Count:    3
     Values:    Hello    World    !
*/ 

.NET Framework

.NET Framework Client Profile

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

Public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

To guarantee the thread safety of the Queue, 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.

Reference