MessagePriority Enumeration
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MessagePriority Enumeration

 

Specifies the priority Message Queuing applies to a message while it is en route to a queue, and when inserting the message into the destination queue.

Namespace:   System.Messaging
Assembly:  System.Messaging (in System.Messaging.dll)

public enum MessagePriority

Member nameDescription
AboveNormal

Between High and Normal message priority.

High

High message priority.

Highest

Highest message priority.

Low

Low message priority.

Lowest

Lowest message priority.

Normal

Normal message priority.

VeryHigh

Between Highest and High message priority.

VeryLow

Between Low and Lowest message priority.

The MessagePriority enumeration is used by the Message class's Priority property. This property affects how Message Queuing handles the message both while it is en route and once it reaches its destination. Higher-priority messages are given preference during routing and inserted toward the front of the destination queue. Messages with the same priority are placed in the queue according to their arrival time.

When Message Queuing routes a message to a public queue, the priority level of the message is added to the priority level of the public queue (which you can access through the MessageQueue class's BasePriority property). The priority level of the queue has no effect on how messages are placed in the queue, only on how Message Queuing handles the message while en route.

Base priority applies only to public queues. For a private queue, the base priority is always zero.

You can set a meaningful priority only for non-transactional messages. Message Queuing automatically sets the priority for transactional messages to Lowest, which causes transactional message priority to be ignored.

The following example sends two messages of different priorities to the queue, and retrieves them subsequently.

using System;
using System.Messaging;

namespace MyProject
{

	/// <summary>
	/// Provides a container class for the example.
	/// </summary>
	public class MyNewQueue
	{

		//**************************************************
		// Provides an entry point into the application.
		//		 
		// This example sends and receives a message from
		// a queue.
		//**************************************************

		public static void Main()
		{
			// Create a new instance of the class.
			MyNewQueue myNewQueue = new MyNewQueue();

			// Send messages to a queue.
			myNewQueue.SendMessage(MessagePriority.Normal, "First Message Body.");
			myNewQueue.SendMessage(MessagePriority.Highest, "Second Message Body.");

			// Receive messages from a queue.
			myNewQueue.ReceiveMessage(); 
			myNewQueue.ReceiveMessage();

			return;
		}


		//**************************************************
		// Sends a string message to a queue.
		//**************************************************

		public void SendMessage(MessagePriority priority, string messageBody)
		{

			// Connect to a queue on the local computer.
			MessageQueue myQueue = new MessageQueue(".\\myQueue");

			// Create a new message.
			Message myMessage = new Message();

			if(priority > MessagePriority.Normal)
			{
				myMessage.Body = "High Priority: " + messageBody;
			}
			else myMessage.Body = messageBody;

			// Set the priority of the message.
			myMessage.Priority = priority;


			// Send the Order to the queue.
			myQueue.Send(myMessage);

			return;
		}


		//**************************************************
		// Receives a message.
		//**************************************************

		public  void ReceiveMessage()
		{
			// Connect to the a queue on the local computer.
			MessageQueue myQueue = new MessageQueue(".\\myQueue");

			// Set the queue to read the priority. By default, it
			// is not read.
			myQueue.MessageReadPropertyFilter.Priority = true;

			// Set the formatter to indicate body contains a string.
			myQueue.Formatter = new XmlMessageFormatter(new Type[]
				{typeof(string)});

			try
			{
				// Receive and format the message. 
				Message myMessage =	myQueue.Receive(); 

				// Display message information.
				Console.WriteLine("Priority: " + 
					myMessage.Priority.ToString());
				Console.WriteLine("Body: " + 
					myMessage.Body.ToString());
			}

			catch (MessageQueueException)
			{
				// Handle Message Queuing exceptions.
			}

			// Handle invalid serialization format.
			catch (InvalidOperationException e)
			{
				Console.WriteLine(e.Message);
			}

			// Catch other exceptions as necessary.

			return;
		}
	}
}

.NET Framework
Available since 1.1
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