Thanks very much Hans, and thanks for such a clear explanation.
I have a tendency to think myself into corners sometimes ;�)
> -----Original Message-----
> From: Hans Liebenberg [mailto:[EMAIL PROTECTED]]
> Sent: 16 July 2001 15:58
> To: [EMAIL PROTECTED]
> Subject: Re: concurrent access to variables with class or block scope
>
>
> Hi Paul,
>
> Your question relates more to general programming then servlets
> specifically.
> If from with in a method you create an object x:
> MyObject x = new MyObject()
>
> It doesn't matter how many threads access the members of x as
> long as each
> one create a new instance of x as above.
>
> >>But surely, if two requests (threads) run through this
> block at the same
> >>time there is still a possibility of a problem with data integrity?
>
> ..method variables never share the same address space for
> multiple threads.
> The only time you may have this is if your method is declared
> as static
> accessing static variables.
>
> As far as multi threaded servlets are concerned you should
> never have member
> variables unless they are to be shared amongst all threads.
>
>
> So for your servlet, rather create an object that handles
> your for request
> say MyRequestHandler, and create a new Instance of the
> RequestHandler for
> each thread (as above) and you can have as many member
> variables as you want
> :)
>
> -----Original Message-----
> From: A mailing list for discussion about Sun Microsystem's
> Java Servlet
> API Technology. [mailto:[EMAIL PROTECTED]]On
> Behalf Of Paul
> Foxton
> Sent: 16 July 2001 15:22
> To: [EMAIL PROTECTED]
> Subject: concurrent access to variables with class or block scope
>
>
> Hi all,
>
> I've been wondering about the fact that concurrent requests
> to a servlet
> will result in a new thread being created to access the same
> instance of the
> servlet as long as singleThreadModel is not implemented with
> reference to
> the following:
>
> If you have a servlet which accesses a database, and request
> parameters from
> an HTML form are used to build the SQL where clause, if these request
> parameters are stored in class instance variables (i.e.
> declared at the
> beginning of the class and outside of any methods, so class
> scope), would
> this mean that there is a possibility of data being overwritten in the
> middle of 2 or more concurrent requests and therefore compromising the
> integrity of the data retrieved from the database?
>
> If so, I would have thought that the way around this is to
> store the values
> from the request parameters in variables declared inside
> methods, which
> would then have block scope within that method.
>
> But surely, if two requests (threads) run through this block
> at the same
> time there is still a possibility of a problem with data integrity?
>
> This doesn't seem quite right to me tho, because then you
> would have to
> synchronize access to any method or variable which was used
> to build an sql
> query or update.
>
> Can anyone clarify?
>
> Sorry if this is an obvious question. I've read through the
> documentation on
> threads in servlets at Suns java site, but am still a little confused.
>
> Thanks,
>
> Paul
>
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