"static" means there is only one copy of the data. This is available to all
users of an application. If one user changes it, it is changed for all users
.
You need to study the difference between the ASP.NET Application object vs.
what is "static" - they have similar features but are not the same thing. An
Application is a running instance of your web site in IIS, to put it in
simplest terms.
--Peter
"Inside every large program, there is a small program trying to get out."
http://www.eggheadcafe.com
http://petesbloggerama.blogspot.com
http://www.blogmetafinder.com
"Dave" wrote:
> I have a global.asax file with Application_Start defined and create some
> static data there and in another module used in the asp.net application an
d
> I realize that static data is shared amongst child apps of an IIS
> application and can be used by multiple users during the application life
> cycle and for multiple page loads for the same or different page under a
> root application.
> What I don't understand and need to know is whether that static data would
> be shared by ALL users of my application on a single server if my
> application was loaded at all or whether it is possible to have my
> application loaded multiple times such that each loading of my application
> has its own set of static data that is potentially shared by multiple user
s.
> Exactly what is an asp.net "application instance" in terms of windows
> process, thread and object terminology which I understand well - is it a
> user's sequenced use of the loaded assembly, concurrent thread usage of an
> assembly or is it multiple loads of an assembly each of which can be used
by
> multiple users/threads?
> As an analogy, let's say I write a multi threaded desktop app and allowed
> multiple threads to use an object called X that was created by the main
> thread. If that object X had static data then all threads in one process
> that loaded my application would share that data in X even if each thread
> had its own instance of X. But if I loaded 2 copies of my desktop
> application (like running 2 copies of notepad.exe), each process would hav
e
> only one instance of object X static data no matter how many isntances of
X
> and each set of X static data would be shared by multiple threads in that
> process but the staic data would not be shared between processes.
> My concern is what scope I must lock at for all users of my asp.net
> application on one machine. Can there be multiple copies of my static data
?
> One for each asp.net "application instance" or whether instance is just
> referring to the fact that multiple users can be sharing the same static
> data in the module that was loaded for the benefit of multiple users which
I
> believe I read are sequenced thru one at a time. Or do I really have to
> worry about some users sharing one set of static data for one loading of m
y
> application and another set of users sharing another set of static data
> because my asp.net application was loaded again for them?
> Hope I made myself clear. If I can have multiple sets of users each with
> their own shared static data then I need to somehow lock across the multip
le
> copies of the static data.
> So to summarize:
> 1. Can/must a C# lock be used for static data for ALL users on one machine
-
> depends if users are sequenced thru the application. Or is this totally
> insufficient to protect a shared resource under asp.net?
>
> 2. Or rather must I somehow externally [like named semaphores] synchronize
> across multiple application instances to protect that truly only one user
at
> a time on a given machine can modify a resource similar to what I would ne
ed
> to do if I had multiple desktop processes running on one machine that had
to
> sequence use of a resource one at a time?
> Whew...thanks!
> Dave
>Peter,
Thanks but this does not answer my question [which I overly stated I think]
which you misunderstood and would like you to reread if you would. I know
what static is just fine, at least from the desktop or server exe
application perspective and it is not true that there can only be one
instance of static data on a machine. In a desktop or server exe
application, if two .exe modules are loaded into memory as 2 separate
processes they each have their own copy of the static data in my program and
in fact do NOT share that data.
What I don't know is how asp.net works in this regard. If 1000 users all hit
the same web page at roughly the same time, will there truly be only one
copy of the static data for all those users or is it possible that
IIS/asp.net could start multiple appdomains/processes whatever that would
cause more than one instance of my static data to exist, say 400 using one
copy and 600 using the other. Perhaps this is only an issue if the case of a
web garden which supposedly starts additional worker threads though I'm not
sure what their effect is on instances of my code or data. I am not
concerned about the case of a web farm where different machines are
involved. One use of knowing how this works for sure is to determine if I
can do a "lock (object)" so as to serialize access to a chunk of code that
let's say updates a file shared by all child apps of an IIS application. I
have also read that asp.net serializes users through an application instance
which does not make a lot of sense to me as that would certainly ruin
performance scaling so am not sure if the asp.net app is expected to be
reentrant or not.
What I am asking is if there somehow can be multiple instances of my static
data on the same machine due to IIS loading multiple copies to help scale
servicing a large number of users. I have read both ways (see below) - that
all users truly share the same application data and that only users running
the same application share static or application data but that there can be
multiple instances loaded with each being shared by multiple users.
And for all purposes that I can see having indeed read about them I see no
discernable difference between using application state and static variables
in an asp.net application and would like you to point out any difference in
result. In fact, I have also read it is no longer suggested one use
application state.
Thanks,
Dave
From
http://findarticles.com/p/articles/..._n15717172/pg_1 -
talks about sets of users sharing different instances but in a manner that
does not clear things up:
"However, what I just said isn't the full story. You don't get just one
HttpApplication. That's where it gets bizarre. The ASP.NET system actually
creates multiple instances of HttpApplication (or of your derived class in
Global.asax) in order to handle multiple requests. The whole idea is so that
IIS and the ASP.NET system can handle high-performance Web sites that get
heavy traffic.
Even though there are multiple HttpApplication instances, there's still no
guarantee which of these are shared among which users. Each user accessing
the site does not necessarily get his own instance of HttpApplication. In
general, you don't want to make any assumptions about the individual
instances of HttpApplication. And remember, even though there may be
multiple HttpApplication instances, only one instance of the application
itself is running on the server."
----
----
"Peter Bromberg [C# MVP]" <pbromberg@.yahoo.NoSpamMaam.com> wrote in message
news:5C4AF146-0B5D-494E-89AA-9C07F34CC28B@.microsoft.com...
> "static" means there is only one copy of the data. This is available to
> all
> users of an application. If one user changes it, it is changed for all
> users.
> You need to study the difference between the ASP.NET Application object
> vs.
> what is "static" - they have similar features but are not the same thing.
> An
> Application is a running instance of your web site in IIS, to put it in
> simplest terms.
> --Peter
> "Inside every large program, there is a small program trying to get out."
> http://www.eggheadcafe.com
> http://petesbloggerama.blogspot.com
> http://www.blogmetafinder.com
>
> "Dave" wrote:
>
Hi Peter,
Here is at least one other opinion on static vs. application object where
they argue that static is better since the data can be in more readily
available form. And the second link argues it should not even be used. Truly
would like to know what you see as the differences. Thanks, Dave
http://www.bloggingdeveloper.com/po...
n-Object.aspx
http://findarticles.com/p/articles/..._n15717172/pg_7
"Dave" <dave@.nospam.com> wrote in message
news:OYN%23xvAKIHA.280@.TK2MSFTNGP03.phx.gbl...
> Peter,
> Thanks but this does not answer my question [which I overly stated I
> think] which you misunderstood and would like you to reread if you would.
> I know what static is just fine, at least from the desktop or server exe
> application perspective and it is not true that there can only be one
> instance of static data on a machine. In a desktop or server exe
> application, if two .exe modules are loaded into memory as 2 separate
> processes they each have their own copy of the static data in my program
> and in fact do NOT share that data.
> What I don't know is how asp.net works in this regard. If 1000 users all
> hit the same web page at roughly the same time, will there truly be only
> one copy of the static data for all those users or is it possible that
> IIS/asp.net could start multiple appdomains/processes whatever that would
> cause more than one instance of my static data to exist, say 400 using one
> copy and 600 using the other. Perhaps this is only an issue if the case of
> a web garden which supposedly starts additional worker threads though I'm
> not sure what their effect is on instances of my code or data. I am not
> concerned about the case of a web farm where different machines are
> involved. One use of knowing how this works for sure is to determine if I
> can do a "lock (object)" so as to serialize access to a chunk of code that
> let's say updates a file shared by all child apps of an IIS application. I
> have also read that asp.net serializes users through an application
> instance which does not make a lot of sense to me as that would certainly
> ruin performance scaling so am not sure if the asp.net app is expected to
> be reentrant or not.
> What I am asking is if there somehow can be multiple instances of my
> static data on the same machine due to IIS loading multiple copies to help
> scale servicing a large number of users. I have read both ways (see
> below) - that all users truly share the same application data and that
> only users running the same application share static or application data
> but that there can be multiple instances loaded with each being shared by
> multiple users.
> And for all purposes that I can see having indeed read about them I see no
> discernable difference between using application state and static
> variables in an asp.net application and would like you to point out any
> difference in result. In fact, I have also read it is no longer suggested
> one use application state.
> Thanks,
> Dave
> From
> http://findarticles.com/p/articles/..._n15717172/pg_1 -
> talks about sets of users sharing different instances but in a manner that
> does not clear things up:
> "However, what I just said isn't the full story. You don't get just one
> HttpApplication. That's where it gets bizarre. The ASP.NET system actually
> creates multiple instances of HttpApplication (or of your derived class in
> Global.asax) in order to handle multiple requests. The whole idea is so
> that IIS and the ASP.NET system can handle high-performance Web sites that
> get heavy traffic.
> Even though there are multiple HttpApplication instances, there's still no
> guarantee which of these are shared among which users. Each user accessing
> the site does not necessarily get his own instance of HttpApplication. In
> general, you don't want to make any assumptions about the individual
> instances of HttpApplication. And remember, even though there may be
> multiple HttpApplication instances, only one instance of the application
> itself is running on the server."
> ----
----
> "Peter Bromberg [C# MVP]" <pbromberg@.yahoo.NoSpamMaam.com> wrote in
> message news:5C4AF146-0B5D-494E-89AA-9C07F34CC28B@.microsoft.com...
>
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