Re: Dynamically introducing code into the application
On 2008-09-02 08:45, Bala wrote:
On Sep 1, 9:35 pm, Erik Wikstr??m <Erik-wikst...@telia.com> wrote:
On 2008-09-01 16:48, Bala wrote:
On Sep 1, 7:15 pm, "Alf P. Steinbach" <al...@start.no> wrote:
* Bala:
1. Suppose you have a Client application that sends your Server a condition like
(1 == 'A' && 2 == 'B') || (3 == 10) && (4 >= 200 && 4 <= 500)
You want to introduce this "if" condition dynamically into the
Server and send the result set back to the Client.
Is this possible in any programming language (C, C++ or JAVA)?
Yes to all.
You just have to compile the code.
I cant recompile the code because the server application is running.
Something like i want to hook the code in.... As far as i
understand, compiler based programming languages need precompiled
code, but this piece of if block is going to come in runtime.. How
would i handle this situation?
You compile it to a shared library/DLL and then load that from you
application. Or you use lisp (or a few other dynamic languages) which
can modify themselves.
Please do not quota signatures.
Hi Erik,
I did think about the following approach.
1. If there is no Dynamic linking then i might generate a new source
file, compile it, run and get the results into the parent process
through IPC.
2. If there is Dynamic Linking, then create a new library/dll, load
and execute it and get the results in the parent application.
But the issue to be addressed here are
1. How costly would this be in terms of performance since the
application will be getting such different requests continously.
2. If 2 different Front Ends send me the same query, then i should be
able to recognize them and use the existing shared library instead of
recompiling it.
To be honest I was not really serious when I wrote that reply, either of
those solutions are bad in more ways than one.
The other approach i was thinking of is to be able to use a third
party high performance regular expression parser and evaluater if at
all that is available to execute the query.
If the expressions the user can enter is limited to a reasonable number
I would spend some time to write a parser/evaluator in C++ and use it to
evaluate the expressions. In "The C++ Programming Language" you can see
an example of a quite advanced calculator. If you understand that you
should be able to expand it to solve your expressions too.
If the expressions are of a more complex nature you should go the route
of using some external/embedded evaluator. An embedded language such as
lua or python might be a good idea, just remember to add some check so
you do not allow the users to run whatever they want.
--
Erik Wikstr??m