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C# 4 and .NET 4

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overview ❘ 1359<br />

Laptop Computer,<br />

Independent Client<br />

Message Queuing<br />

Server<br />

figure 46-2<br />

Message Queue<br />

Web Server,<br />

Dependent Client<br />

Message Queue<br />

Message Queuing<br />

Server<br />

Internet<br />

Database<br />

Client<br />

figure 46-3<br />

Message Queue<br />

message queuing features<br />

Message Queuing is part of the Windows operating system. The main features of this service are:<br />

➤<br />

➤<br />

➤<br />

➤<br />

➤<br />

Messages can be sent in a disconnected environment. It is not necessary for the sending <strong>and</strong> receiving<br />

applications to run at the same time.<br />

With express mode, messages can be sent very quickly. Express-mode messages are just stored in<br />

memory.<br />

For a recoverable mechanism, messages can be sent using guaranteed delivery. Recoverable messages<br />

are stored within files. They are delivered even in cases when the server reboots.<br />

Message queues can be secured with access-control lists to define which users can send or receive<br />

messages from a queue. Messages can also be encrypted to avoid network sniffers reading them.<br />

Messages can be sent with priorities so that high-priority items are h<strong>and</strong>led faster.<br />

Message Queuing 3.0 supports sending multicast messages.<br />

Message Queuing 4.0 supports poison messages. A poison message is one that isn’t getting resolved. You can<br />

define a poison queue where unresolved messages are moved. For example, if the job after reading the message<br />

from the normal queue was to insert it into the database, but the message did not get into the database <strong>and</strong><br />

thus this job failed, it would get sent to the poison queue. It is someone’s job to h<strong>and</strong>le the poison queue —<br />

<strong>and</strong> that person should deal with the message in a way that resolves it.<br />

➤<br />

Message Queuing 5.0 supports more secure authentication algorithms <strong>and</strong> can h<strong>and</strong>le a larger number<br />

of queues. (Message Queuing 4.0 had performance problems with several thous<strong>and</strong> queues.)<br />

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