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Asynchronous Web Services

Asynchronous Web Services. Jaliya N. Ekanayake. Basics of Web Services. Simple Web Service Invocations. Example of Synchronous Service Invocation. Service takes some time to complete Client is waiting for the response Example of Asynchronous Service Invocation

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Asynchronous Web Services

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  1. Asynchronous Web Services Jaliya N. Ekanayake

  2. Basics of Web Services

  3. Simple Web Service Invocations • Example of Synchronous Service Invocation. • Service takes some time to complete • Client is waiting for the response • Example of Asynchronous Service Invocation • Service takes some time to complete • Client is waiting for the response

  4. Some Use Cases • Time consuming web services • long-lived operations • batch processing • peer to peer programs • event driven application models. • Web services that leverage The client can be a Reactive Application • Client can be a server to some other clients. So the blocking is not acceptable.

  5. Some Use Cases contd.. • User may not need to wait for the responses • User is doing some batch submission. • E.g. A bank submitting credit card information to a service provider. • User can check for responses after sending few invocations. • The response from a service represents a collective information. • User need the response after some time. • E.g. A batch submission process, the result will be available in the next day.

  6. Supporting the Asynchrony • Protocol level asynchrony • E.g. JMS can be used to invoke the services asynchronously. • Client subscribes to a topic and return • Response will be delivered to client through the JMS Queue • Client Asynchrony Patterns • Fire and Forget • Callbacks • Polling • Service Asynchrony

  7. Client Machine Server 1 Invoke 2 Send Client Proxy Client Service 3 Return Client Side Asynchrony • Fire and Forget. • Invokes the service and return immediately without ever bothering about a response. • Issues • No waiting. Client can immediately resume the thread. • Easy for the developers • Loosely coupled • No way to verify whether the request has been sent or not.

  8. Fire and Forget • Code Snippet • Example>>

  9. Client Machine Server 2 Send 1 Invoke Client Proxy Client Service 3 Return a Poll Object Polling and getting back the result Poll Object Set the Response Client Side Asynchrony • Polling • Client repeatedly poll for the availability of the results, while performing some other task. • Issues • Client has to wait polling • Client has to handle the complexity of this polling operation • Response can be retrieved asynchronously

  10. Polling • Code Snippet • Example>>

  11. Client Machine Server 3 Send 2 Invoke Client Proxy Client Service 1 Creates a Callback Object Callback 4 Response is dispatched to the callback by the client proxy Client Side Asynchrony • Result Callbacks • Client provides a callback method. Proxy will dispatch the result using the callback method. • Issues • Client has to provide the callback method • Client has to handle the additional complexity • Response can be retrieved asynchronously

  12. Callback • Code Snippet • Example>>

  13. Asynchronous Web Service Model • The service does not “return” anything. • It can send the response (if any) by itself. • Transport may or may not be synchronous • E.g. 1 (HTTP Transport) • Service has a void return type and it will send a response after a while using different HTTP connection • E.g. 2 (One way transport -JMS) • Service sends a response using a new one way transport. • What is required. • Service should have the capability to send the response by itself. • Client should be able to correlate the request and the response • Client should have an addressable endpoint. • Can use WS-Addressing <wsa:relatesTo> for standard correlation.

  14. Client Sender M Service Receiver M Asynchronous Web Service Model contd.. • The model • Features • Service sends the response by itself. • Correlation information contains in the SOAP message itself. • Client has both a Sender and a Receiver.

  15. Support from the Existing Technologies • Microsoft .NET supports the client side asynchrony. • With the WSE 2.0 the service asynchrony is also supported. • Systinet WASP supports the client side asynchrony and WS-Addressing. • Axis 2 (Currently under development) will support both.

  16. Summery • There are many advantages of using asynchronous patterns in implementing web services for B2B, EAI scenarios. • Client Side Asynchrony • Fire & Forget • Polling • Callbacks • Service Asynchrony • Technology support

  17. References • http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnmaj/html/aj2mpsoarch.asp • http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/html/cpconinvokingwebservicesasynchronously.asp • www.fawcette.com/xmlmag/ 2003_02/magazine/practice/dchappell/ • http://www.c-sharpcorner.com/Code/2004/April/AsyncWebServices.asp • http://www.esecurityplanet.com/prodser/article.php/2235201 • http://xml.coverpages.org/ni2004-04-15-a.html

  18. Thank You!

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