ok

as i was reading the wonderfull book

professional asp 3.0, (chapter 15, page 615 bottom and

page 618 top to middle-

where it says that components in vb should not be 

stored in session variables)

, which i already love,

i thought how i could build a small chat aplication

with asp and vb.



in a few words said my problems are:



- i think that each user should be reprezented by an

instance of

a compoment written in vb. the problem is that i read

that these 

objects should not be stored as session variables.so

how could i

put a mesage ( say this is a proprety of the component

with read only

asignement) from one object to another without finding

them anymore in the

memory...without beeing global as a sesion variable

is?

- say i could find a solution to the above issue..but

how about actually transmiting

the message from the server to the client's machine.

say i got the ip of that machine

, but after that..how do i do it with asp...or

vb...beats me...





thank u



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I have a small chat application that sounds similar to what you wanted to

do. I wrote a free-threaded dictionary that is stored in the application

object. Each entry in the dictionary hold an instance of a free-threaded

message queue component that I also  wrote. The site works as such:



- At startup each each session adds itself to the dictionary, naming the key

after the session ID:



function Session_OnStart()

{

Application("chatdictionary").Add(Session.SessionID, new

ActiveXControl("ipni.messagequeue"));

}



- Each client then runs a remote script that reads every queue except its

own, and sends the received chat messages back to the browser as an XML

string:



function ReadMessages()

{



var szChatMessages = "<document>";



for(i=1;i<=Application("chatdictionary").count;i++)

{

szChatMessages = szChatMessages + "<message>";

szChatMessages = szChatMessages +

Application("chatdictionary").item(i).Read();

szChatMessages = szChatMessages + "</message>";

}



szChatMessages = szChatMessages  + "</document>";



return szChatMessages;

}



- Each client also runs a remote script that writes to his own queue when

the user presses send:



function SendMessage(szMessage)

{

var objMyQ = Application("chatdictionary").Item(Session.SessionID);

objMyQ.Write(szMessage);

}





In this way, a simple chat room is created. 



It is extremely important for all objects to be free-threaded because access

to the dictionary and the queue can be concurrent and therefore must be

thread-safe.









You can learn more about remote scripting at

http://msdn.microsoft.com/scripting. If you need some pointers on creating

those dictionaries or queues I can help, but hands down, I can only help if

you know C++  : )



J





-----Original Message-----

From: Dragos Tudose [mailto:dtudose@y...]

Sent: Monday, January 14, 2002 1:46 PM

To: ASP components

Subject: [asp_components] components in vb vs session variables





ok

as i was reading the wonderfull book

professional asp 3.0, (chapter 15, page 615 bottom and

page 618 top to middle-

where it says that components in vb should not be 

stored in session variables)

, which i already love,

i thought how i could build a small chat aplication

with asp and vb.



in a few words said my problems are:



- i think that each user should be reprezented by an

instance of

a compoment written in vb. the problem is that i read

that these 

objects should not be stored as session variables.so

how could i

put a mesage ( say this is a proprety of the component

with read only

asignement) from one object to another without finding

them anymore in the

memory...without beeing global as a sesion variable

is?

- say i could find a solution to the above issue..but

how about actually transmiting

the message from the server to the client's machine.

say i got the ip of that machine

, but after that..how do i do it with asp...or

vb...beats me...





thank u



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$subst('Email.Unsub').

thank u..i'll have to sit and chew the code for a

while as i'm a beginner in vb.



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ok

first thing to say..

i noticed your components are in C not in VB..which

explains how u made them free threaded



then ..

i'm thinking about the msmq service.

in the chat project i'm studying the posibility 

of each user beeing served as a msmq component put 

in the dictionary..put in the application object as u told me.





messages are ariving from the users to each queue he or she owns.

in paralel a service or an exe on the server must process the

incoming synchronously or asynchronously.



one problem  is that in asp..as i read form pro asp u can't do it async.

that leaves me only the sync mode to deal with.



ok...but suppose we have this moment in time:





a user says: "how are u?"



another answers: "fine"





how can i control that in the process of harvesting the messages 

(sync..mode) and 

putting all in a variable and sending this variable to each user's 

screen..i don't mess up like this:



"fine"



"how are u?"



thank u again

I understand your question, but I just wanted to clarify that I'm not using

MSMQ myself, though I think it will do a fine job for what you're after if

it has automation interfaces.



Anyway, I think to keep the messages straight you will want two things:



1. Queue management - When you post a message (publisher), the publisher

should publish his message to all queues except his own. While he is

publishing, he really should lock ALL subscriber queues using some global

semaphore (see next point) to ensure that he isn't half done publishing

before someone else sees his message, and replies before the first message

has been completely disseminated.



2. Concurrency management - I satisfied my concurrency management through a

COM object I call a lock manager. I wrote this lock manager because the only

really good concurrency object in IIS is the Application.Lock method. The

bad thing about Application.Lock is that it's global; even simulation of

multiple locks with arrays and counters ultimately boils down to that single

lock, which doesn't scale very well. Anyway, back to the point - if you

design this thing such that all subscribers agree to acquire the lock before

they publish, you guarantee that the messages will come out in order. So if

one guy says "hi", his remote script goes to the server, locks all the

queues (using whatever lock you decide to use), publishes "Hi" to all

participants, then releases the lock. While you are publishing right up to

the very last nanosecond before you release the lock, subscribers may be

pulling the message you just sent off of their queues. Further more, suppose

that you are about half way done publishing when the first recipient already

writes back "hi back". In order to send the "hi back" message, his publish

routine by design must attempt to acquire the lock, and in doing so, will

block until the first message "hi" has been published to all queues, and

then acquire the lock as soon as the "hi" publisher releases it. This is a

very classic multi-threading paradigm which should suite your needs quite

well. 



Lastly, to get this thing up and running, you can certainly prototype using

the Application.Lock method - just keep in mind the design could be enhanced

in the future. So all things said, your remote scripts would look something

like:



function Publish(szMessage)

{

Application.Lock();



for all subscribers except me

{

subscriber->publish(szMessage);

}



Application.Unlock();

}



function Read()

{



while still messages in my Q

build XML string with messages

{

<document>

<message>

hi there

yo anyone here

yes

</message>

<message>

go away

</message>

</document>

}



}









Note that because the publish method does the locking, and the queue MUST be

free threaded, it's safe to read the queue even while it's being written to,

and therefore you don't need a lock to read.



Hope this helps!!





J



-----Original Message-----

From: dtudose@y... [mailto:dtudose@y...]

Sent: Thursday, January 17, 2002 2:25 PM

To: ASP components

Subject: [asp_components] RE: components in vb vs session variables





ok

first thing to say..

i noticed your components are in C not in VB..which

explains how u made them free threaded



then ..

i'm thinking about the msmq service.

in the chat project i'm studying the posibility 

of each user beeing served as a msmq component put 

in the dictionary..put in the application object as u told me.





messages are ariving from the users to each queue he or she owns.

in paralel a service or an exe on the server must process the

incoming synchronously or asynchronously.



one problem  is that in asp..as i read form pro asp u can't do it async.

that leaves me only the sync mode to deal with.



ok...but suppose we have this moment in time:





a user says: "how are u?"



another answers: "fine"





how can i control that in the process of harvesting the messages 

(sync..mode) and 

putting all in a variable and sending this variable to each user's 

screen..i don't mess up like this:



"fine"



"how are u?"



thank u again

 




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$subst('Email.Unsub').

thanks J.i'll study in every detail what u send me

here.





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