Concurrency in flowscript

[Gerry Kaplan <gk...@kaplansoftware.com>]

I'm curious about how Cocoon handles concurrency under the following
circumstances.

Let's say that a pipeline calls a flowscript function to show a form. When
the user completes the form and submits, the flowscript reads an XML
document, then adds the data from the form to the document, and then
re-saves the document.

What would happen if, at the exact same moment, another user called upon the
same pipeline and displayed the form, then submitted. But the first user's
save hasn't occurred yet. When the 2nd user saves the document, it will
overwrite any changes that the first user added.

The real scenario is a self-registration form. The application keeps a
single XML document that contains a "user" node for each user. When the user
self registers, their entries are added into the users.xml document. Does
Cocoon allow multiple instances of the same form to execute simultaneously?
Or is there a "synchronized" type of keyword in flowscript that would
prevent both users from reading/updating/writing the same XML document?

Gerry

RE: Concurrency in flowscript

[Gerry Kaplan <gk...@kaplansoftware.com>]

Thanks much for your feedback.

In fact, my current design creates a separate xml file for each user, and I
started wavering on whether it was better to keep them all in one file or
not. Ultimately, I will use an LDAP. I need to find a Cocoon consultant who
has experience with using an LDAP, as I have limited LDAP experience. This
is the only time in the app that concurrency is an issue. An LDAP would be a
great solution to user management for sure.

Thanks again!

Gerry 

-----Original Message-----
From: Ralph Goers [mailto:Ralph.Goers@dslextreme.com] 
Sent: Monday, September 12, 2005 12:32 AM
To: users@cocoon.apache.org
Subject: Re: Concurrency in flowscript

To make a long story short, Cocoon would be like any other application in
your scenario.  You have to provide the synchronization into the pipeline.
You have to add the transaction support so that the second user would be
informed that the document had changed by the first user while he was
editing it.

However, as far as I can see this has nothing to do with the forms.  I'm
pretty sure they will execute independently as each flow will create its own
form object.

Does your design really call for a single users.xml document?  I just can't
imagine that scaling very well - it would get rather huge.  I could imagine
each user having an entry in a database table or in an LDAP repository and
every user getting their own user.xml document though.  That wouldn't have
any of the problems you are mentioning.  I seem to recall some of the
samples using a users.xml to look up a user during authentication, but those
are just sample pipelines and not necessarily meant to be a production
design.  You can use other mechanisms to perform the authentication.

Ralph

Gerry Kaplan wrote:

>I'm curious about how Cocoon handles concurrency under the following 
>circumstances.
>
>Let's say that a pipeline calls a flowscript function to show a form. 
>When the user completes the form and submits, the flowscript reads an 
>XML document, then adds the data from the form to the document, and 
>then re-saves the document.
>
>What would happen if, at the exact same moment, another user called 
>upon the same pipeline and displayed the form, then submitted. But the 
>first user's save hasn't occurred yet. When the 2nd user saves the 
>document, it will overwrite any changes that the first user added.
>
>The real scenario is a self-registration form. The application keeps a 
>single XML document that contains a "user" node for each user. When the 
>user self registers, their entries are added into the users.xml 
>document. Does Cocoon allow multiple instances of the same form to execute
simultaneously?
>Or is there a "synchronized" type of keyword in flowscript that would 
>prevent both users from reading/updating/writing the same XML document?
>
>Gerry
>  
>


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Re: Concurrency in flowscript

[Ralph Goers <Ra...@dslextreme.com>]

To make a long story short, Cocoon would be like any other application 
in your scenario.  You have to provide the synchronization into the 
pipeline.  You have to add the transaction support so that the second 
user would be informed that the document had changed by the first user 
while he was editing it.

However, as far as I can see this has nothing to do with the forms.  I'm 
pretty sure they will execute independently as each flow will create its 
own form object.

Does your design really call for a single users.xml document?  I just 
can't imagine that scaling very well - it would get rather huge.  I 
could imagine each user having an entry in a database table or in an 
LDAP repository and every user getting their own user.xml document 
though.  That wouldn't have any of the problems you are mentioning.  I 
seem to recall some of the samples using a users.xml to look up a user 
during authentication, but those are just sample pipelines and not 
necessarily meant to be a production design.  You can use other 
mechanisms to perform the authentication.

Ralph

Gerry Kaplan wrote:

>I'm curious about how Cocoon handles concurrency under the following
>circumstances.
>
>Let's say that a pipeline calls a flowscript function to show a form. When
>the user completes the form and submits, the flowscript reads an XML
>document, then adds the data from the form to the document, and then
>re-saves the document.
>
>What would happen if, at the exact same moment, another user called upon the
>same pipeline and displayed the form, then submitted. But the first user's
>save hasn't occurred yet. When the 2nd user saves the document, it will
>overwrite any changes that the first user added.
>
>The real scenario is a self-registration form. The application keeps a
>single XML document that contains a "user" node for each user. When the user
>self registers, their entries are added into the users.xml document. Does
>Cocoon allow multiple instances of the same form to execute simultaneously?
>Or is there a "synchronized" type of keyword in flowscript that would
>prevent both users from reading/updating/writing the same XML document?
>
>Gerry
>  
>


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