Re: Witango-Talk: Thread Safe Class file

[Customer Support]

The thread safe property for a TCF in the dev studio is actually no  
longer relevant in the Witango 5 Server as each request runs in its own  
thread rather than being passed into different resource threads.  This  
was only an issue in the cooperatively threaded T2K server and how it  
worked.  The architecture of the new server does not use this property  
and there is no penalty in performance when using TCFs, except for the  
instantiation of the object.

TCFs aside you do have to be careful with the preemptive threading in  
the Witango 5 Server with shared scopes variable (custom scope,  
application scope) as you can have one request change a variable that  
another thread may be using.  Take for instance a while action using a  
custom scoped variable in one thread like this (pseudo code):

myScope$MyVar=0
WHILE (myScope$MyVar != 100) {
        Other Actions
        Increment myScope$MyVar
        }
If another thread is started and runs the same code there is a chance  
that both could increment myScope$MyVar simultaneously.  Let say that  
the value of myScope$MyVar is 99 when this occurs, there is a chance  
that this loop will never exit as myScope$MyVar is equal to 101 before  
the end of the loop iteration.  This would create an infinite loop.   
Request scope is the safest scope followed by user scope which would  
only have this type of issue in a framed site.

I will let the doc writers know to update the manual and engineering so  
they can decide what to do with the dev studio.

Witango Support

On 05/03/2004, at 3:59 PM, <[EMAIL PROTECTED]> wrote:



I have noticed that for any TCF object, no matter how simple (even an  
empty
one), the property reads "Thread Safe:  No".

According to the documentation:
"If the field indicates No (not thread safe), Witango Server waits for  
one
execution of the instance to complete before it starts another, to  
avoid any
interference between the two. From the user's perspective, the  
difference is
in performance only. "
If this is true, what difference does it make if we have an algorithm  
to
handle critical sections?

For all practical reasons, once one creates such an object there is a
performance penalty.
Perhaps the documentation should more clearly state this problem with  
TCFs.

The "thread safe" subject is so briefly mentioned in the manual is  
difficult
to understand why is it mentioned at all...

Where do I go wrong?

- Mike.



-----Original Message-----
From: Fogelson, Steve [mailto:[EMAIL PROTECTED]
Sent: Monday, March 01, 2004 12:05
To: '[EMAIL PROTECTED]'
Subject: RE: Witango-Talk: Thread Safe Class file
Actually, I read about "thread safe" when reviewing Witango  
documentation
for class files. Seemed like it would be advantageous with multi  
threading
version 5. Maybe it is no big deal not to be thread safe. I just  
thought it
would allow Witango to handle more concurrent requests.

I checked a couple of my class files (per documentation) to see if  
they were
thread safe and it indicates they are not. So I was wondering:

1) Do we have the ability to change this flag or does the app studio
determine if it is?
2) What is required of a class file in order to be thread safe
Thanks for the comments

Steve

-----Original Message-----
From: Robert Shubert [mailto:[EMAIL PROTECTED]
Sent: Monday, March 01, 2004 1:28 PM
To: [EMAIL PROTECTED]
Subject: RE: Witango-Talk: Thread Safe Class file
Oops, my bad ... I was replying to Bill's post, who replied to you,  
replying
to Bill who replied to Steve ... I think. :)

-----Original Message-----
From: Alan Wolfe [mailto:[EMAIL PROTECTED]
Sent: Monday, March 01, 2004 1:36 PM
To: [EMAIL PROTECTED]
Subject: Re: Witango-Talk: Thread Safe Class file
Steve was asking actualy so i dont know what his intentions are, i was  
just
tossing in my 2 cents (:

----- Original Message -----
From: "Robert Shubert" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Monday, March 01, 2004 10:25 AM
Subject: RE: Witango-Talk: Thread Safe Class file

Alan,

If you mean to make a TCF that is thread safe, it depends on why you
need it thread safe. Normally just using the method scope for all
action
internal to the TCF is enough, however if you need to deal with
external
dependencies, ie writing to two different log files in tandem, then
you
need to use a higher scope, such as instance, or domain to record your
busy flag. Since I have more than one server, I can only depend on my
database as a single point of reference, and therefore set and release
a
flag in my database to solve certain overrun problems. Make sure to
alert yourself or log when contention occurs since it can become a
problem can cause congestion if it goes wrong.
Robert

-----Original Message-----
From: Alan Wolfe [mailto:[EMAIL PROTECTED]
Sent: Monday, March 01, 2004 12:42 PM
To: [EMAIL PROTECTED]
Subject: Re: Witango-Talk: Thread Safe Class file
hey Bill, correct me if im wrong but wouldnt this work too?  I just
like
this method because it waits until the other thread is done, so you
dont
have to have code to recheck if it's busy.

while (user$active != 0)
{
  (doing nothing...)
}
user$active = 1;

do the stuff

user$active = 0;

----- Original Message -----
From: "Bill Conlon" <[EMAIL PROTECTED]>
To: "Witango-Talk" <[EMAIL PROTECTED]>
Sent: Monday, March 01, 2004 9:11 AM
Subject: Re: Witango-Talk: Thread Safe Class file

Here's pseudo code to handle critical sections:

if (user$active>0)
     error return, "sorry, you have a request pending, try again"
else
     user$active=user$active+1
if  (user$active=1)
     process stuff
else
     error return:  "sorry a thread inserted itself between the
first
error check and the processing check"
endif
user$active=user$active-1
good return


Where would I look to find out how to create a "thread safe" class
file?
Steve Fogelson
Internet Commerce Solutions

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Bill Conlon

To the Point
345 California Avenue Suite 2
Palo Alto, CA 94306
office: 650.327.2175
fax:    650.329.8335
mobile: 650.906.9929
e-mail: mailto:[EMAIL PROTECTED]
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