Question for Web Service Buffs

[Web Developer]

I'm trying to understand how async callbacks are possible with web services
since they use HTTP (which is stateless) for their communication protocol.
What happens under the covers to allow services to perform callbacks when
they're complete?

Thanks for your help.

[John Bailo]

Web Developer wrote:

I'm trying to understand how async callbacks are possible with web services
since they use HTTP (which is stateless) for their communication protocol.
What happens under the covers to allow services to perform callbacks when
they're complete?

Thanks for your help.

What allows a web page to be sent back to your browser when you enter a
URL in the location?

[John Bailo]

Web Developer wrote:

I'm trying to understand how async callbacks are possible with web services
since they use HTTP (which is stateless) for their communication protocol.
What happens under the covers to allow services to perform callbacks when
they're complete?

Thanks for your help.

What allows a web page to be sent back to your browser when you enter a
URL in the location?

[Web Developer]

Responding to a question with a question doesn't quite answer it. Can you
provide any low-level details about how it works?

It seems like the client must be opening a TCP connection (on port 80) that
stays open. Is that right? If so, in the async communication, how does the
web server know when to close the connection?

Thanks.

"John Bailo" wrote:

Web Developer wrote:

I'm trying to understand how async callbacks are possible with web services
since they use HTTP (which is stateless) for their communication protocol.
What happens under the covers to allow services to perform callbacks when
they're complete?

Thanks for your help.

What allows a web page to be sent back to your browser when you enter a
URL in the location?

[Web Developer]

Responding to a question with a question doesn't quite answer it. Can you
provide any low-level details about how it works?

It seems like the client must be opening a TCP connection (on port 80) that
stays open. Is that right? If so, in the async communication, how does the
web server know when to close the connection?

Thanks.

"John Bailo" wrote:

Web Developer wrote:

I'm trying to understand how async callbacks are possible with web services
since they use HTTP (which is stateless) for their communication protocol.
What happens under the covers to allow services to perform callbacks when
they're complete?

Thanks for your help.

What allows a web page to be sent back to your browser when you enter a
URL in the location?

[John Bailo]

Web Developer wrote:

Responding to a question with a question doesn't quite answer it. Can you
provide any low-level details about how it works?

It seems like the client must be opening a TCP connection (on port 80) that
stays open. Is that right?
You just said it was /stateless/.
If so, in the async communication, how does the
web server know when to close the connection?

Thanks.

"John Bailo" wrote:

Web Developer wrote:

I'm trying to understand how async callbacks are possible with web services
since they use HTTP (which is stateless) for their communication protocol.
What happens under the covers to allow services to perform callbacks when
they're complete?

Thanks for your help.

What allows a web page to be sent back to your browser when you enter a
URL in the location?

[John Bailo]

Web Developer wrote:

Responding to a question with a question doesn't quite answer it. Can you
provide any low-level details about how it works?

It seems like the client must be opening a TCP connection (on port 80) that
stays open. Is that right?
You just said it was /stateless/.
If so, in the async communication, how does the
web server know when to close the connection?

Thanks.

"John Bailo" wrote:

Web Developer wrote:

I'm trying to understand how async callbacks are possible with web services
since they use HTTP (which is stateless) for their communication protocol.
What happens under the covers to allow services to perform callbacks when
they're complete?

Thanks for your help.

What allows a web page to be sent back to your browser when you enter a
URL in the location?

[Web Developer]

John,
I have no idea what your statement means, but it's not an answer.

Can anyone else describe what happens when an async callback is made from a
web service?

Thanks.

[Web Developer]

John,
I have no idea what your statement means, but it's not an answer.

Can anyone else describe what happens when an async callback is made from a
web service?

Thanks.

[Dave Stienessen]

If I'm not mistaken, an async call to a web service all happens on the client
side - basically a thread is spawned on the client side to invoke the web
service via the thread pool and when the thread completes the web service
call, it invokes you callback.
HTH
--
Dave Stienessen

"Web Developer" wrote:

John,
I have no idea what your statement means, but it's not an answer.

Can anyone else describe what happens when an async callback is made from a
web service?

Thanks.

[Dave Stienessen]

If I'm not mistaken, an async call to a web service all happens on the client
side - basically a thread is spawned on the client side to invoke the web
service via the thread pool and when the thread completes the web service
call, it invokes you callback.
HTH
--
Dave Stienessen

"Web Developer" wrote:

John,
I have no idea what your statement means, but it's not an answer.

Can anyone else describe what happens when an async callback is made from a
web service?

Thanks.

[Web Developer]

Thanks Dave. That makes sense.

[Web Developer]

Thanks Dave. That makes sense.

[Chris Bova]

Callbacks to the client from a web service (as in, open a connection to
my web browser when you get finished) are not possible/practical.
Usually the way long running async operations are handled is to have
the client check back at a short interval (using the META refresh tag
for example). Each checkback is a separate, stateless, http request. If
they happen to check back after you've finished servicing their
request, display the results, which you have persisted in the meantime
in session state or someplace like that. Check out the "Asynchronous
Wait State Pattern in ASP.NET" article on MSDN for more info and sample
code.

Chris Bova