Synchronous Message Communication with Reply Pattern in Software Use Code 39 Extended in Software Synchronous Message Communication with Reply Pattern

15.3.1 Synchronous Message Communication with Reply Pattern generate, create 3 of 9 barcode none in software projects Specific Terms for GS1 Barcodes The most common form Software Code 39 of software architectural communication pattern for client/server communication is Synchronous Message Communication with Reply, also known as the request/response pattern. Synchronous Message Communication with Reply (Figure 15.7) can involve a single client sending a message to a service and then waiting for a reply, in which case no message queue develops between the client and the service.

However, it is more likely to involve multiple clients interacting with a single service, as described next. In the typical client/server situation, each client sends a request message to a service and waits for a response from it. In this pattern, because there are several clients sending service requests, a message queue can build up at the service.

The client uses synchronous message communication and waits for a response from the service.. component aClien aClient t 1: sendSynchronousMessageWithReply (in request, out response) aService Figure 15.7. Synchronous Message Communication with Reply pattern Designing Client/Server Software Architectures 1: sendBankingTransac tion (in transaction, out response) user interaction : UserClient 2: sendATMTransaction (in transaction, out response) service : BankingService. client : ATMClient Figure 15.8. Examples of the Synchronous Message Communication with Reply pattern: Banking application.

Whether the client us 39 barcode for None es synchronous or asynchronous message communication with the service depends on the application and does not affect the design of the service. Indeed, some of a service s clients may communicate with it via synchronous message communication and others via asynchronous message communication. An example of Multiple Client/Single Service message communication using synchronous message communication with reply is shown in Figure 15.

8, in which the Banking Service responds to service requests from multiple clients, both user clients and ATM clients. Banking Service has a message queue of incoming synchronous requests from the multiple clients. Each ATM Client component sends a synchronous message to Banking Service and then waits for the response.

The service processes each incoming transaction message on a FIFO basis and then sends a synchronous response message to the client. If the client and server are to have a dialog that involves several messages and responses, a connection can be established between them. Messages are then sent and received over the connection.

. 15.3.2 Asynchronous Message Communication with Callback Pattern The Asynchronous Mess barcode 3/9 for None age Communication with Callback pattern is used between a client and a service when the client sends a request to the service and can continue executing without needing to wait for the service response; however, it does need the service response later (Figure 15.9). The callback is an asynchronous response to a client request message sent previously.

This pattern allows the client to execute asynchronously but still follows the client/service paradigm in which a client sends only one message at a time to the service and receives a response from the service.. 1: sendAsynchronousMe ssage ( in message, in callbackHandle) aClient 2: sendCallbackResponse ( in response) aService. Figure 15.9. Asynchronous Message Communication with Callback pattern Architectural Design Server node Client node Client Application Software / GUI software Middleware Operating System Communication Software Service Application S oftware Middleware Operating System, Database Management System Communication Software. network Figure 15.10. Example of middleware in client and server nodes With the callback pat Software USS Code 39 tern, the client sends a remote reference or handle, which is then used by the service to respond to the client. A variation on the callback pattern is for the service to delegate the response to another component by forwarding to it the callback handle..

15.4 MIDDLEWARE IN CLIENT/SERVER SYSTEMS Middleware is a layer Software Code39 of software that sits above the heterogeneous operating system to provide a uniform platform above which distributed applications, such as client/server systems, can run (Bacon 1997). An early form of middleware was the remote procedure call (RPC). Other examples of middleware technology (Szyperski 2003) are Distributed Computing Environment (DCE), which uses RPC technology; Java remote method invocation (RMI); Component Object Model (COM); Jini Java 2 Platform Enterprise Edition (J2EE); and Common Object Request Broker Architecture (CORBA) .

An example of middleware in a client/server con guration is shown in Figure 15.10. On the client node is the client application, which uses a graphical user interface (GUI).

There is a standard operating system, such as Windows, and network communication software, such as TCP/IP (Transmission Control Protocol/Internet Protocol), which is the most widely used protocol on the Internet. A middleware layer sits above the operating system and the network communication software. On the server node is the service application software, which makes use of the middleware services that reside on top of the operating system (e.

g., UNIX, Linux, or Windows), and the network communication software. A le or database management system, usually relational, is used for long-term information storage.

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