On 9/14/06, Jose <jmalv04@gmail.com> wrote:
On 9/14/06, Giovanni Piero Deretta <gpderetta@gmail.com> wrote:
What do you exactly mean with web continuations? Is it session management done with coroutines instead of encoding state in session ids? I will see if i can come up with something. Ideas are wellcome.
The term is used when continuations are used to handle the app flow in web forms. It's one of the most popular topics in advanced web development ! Traditional session handling is done via session ids with cookies but it has big shortcomings when using back button or creating a new browser window plus coding the app flow is not as natural or elegant as it can be with web continuations. Web continuations handle the execution state not just the session state.
Some references below. The basic hello example is a calculator app or a guessing game. The pdf below provides a real world example (a shopping cart)
check section: Web Continuations revolutionizing webapp development http://it.sun.com/eventi/jc05/pdf/2-ProNetics.pdf
Crossing borders: Continuations, Web development, and Java programming http://www-128.ibm.com/developerworks/java/library/j-cb03216/
Yield, Web Continuations! Article shows how to emulate web continuation in .NET framework http://www.codeproject.com/useritems/YeildContinuations.asp
After a quick look I see that there could be some problems on implementing web continuations with coroutines. The problem is that coroutines are a subset of full continuations. One shot continuations and subcontinuations can be implemented with coroutines (and vice versa), but full continuations cannot. A continuation can be restored multiple times, and this behaviour is for example used to implement back button handling (the continuation relative to the previous page state is saved, so it can be restored when the previous state is reloaded). I do not see how this could be implemented with coroutines automatically unless coroutines where deepcopy-able (you could copy a coroutine and then resome that copy). Unfortuantely it is not feasible to make deep copies of them in the current language. As far as i can see, this is the only place where the 'fullness' aspect of web continuations is used. If you can handle the back button problem in some other way or simply ignore the problem, then coroutines are a good way to implement web continuations. BTW, unless I 'm missing something, the .NET implementation has the same limitation. -- Giovanni P. Deretta