Newbie question communicating between 2 progs
garrett at bgb.cc
Mon Jun 10 20:51:43 CEST 2002
Ben Thursfield wrote:
> Peter Hansen schrieb:
>>The question is ambiguous. When you say "frames", the only thing
>>that comes to mind is that you are running Python on client-side
>>Internet Explorer under Windows, as scripts in two different parts
>>of a window (the frames) simultaneously. I think you must have
>>meant something different however.
>>Could you please describe more about your environment? The
>>term "frame" can mean a number of things.
> That's right. I am running 2 cgi-scripts in two different frames of the
> browser, the one should only print an array into the frame and the other one
> communicates with a server. I decided to split the programm up because i want
> to refresh the printing frame every second. The main frame changes the array
> the second frame prints it out. My host has Python installed, so the
> #usr/bin/python method works fine.
> So the question is how can the programm responsible for printing out the array
> access the array defined in the other programm.
This is a suprisingly hard problem.
The two programs are only running while the frame they handle is being
generated. They shutdown and start up on each refresh request. I'm assuming
you aren't using some form of server push, which has it's own problems. They
don't save any state at all between refreshes of the same page. This means you
have to solve the problem of having a program communicate it's state to
itself! The good news is that when the program can communicate to itself, you
can use the same mechanism to communicate with the other frame.
should be visible to all pages on the local site (you can control this) so
they will allow you scripts to communicate with themselves and each other. You
can store a fair amount in one (I'm not sure what the size limit is), and it
can be binary.
A few warnings.
Some people disable cookies. This can totally break your site.
All cookies are always uploaded as part of every page request everywhere
they are visible. This means that you shouldn't make them too large or you
will slow your site. If they are big, try to restrict cookie visibility to
just the pages that really need them. You can specify where the cookies are
visible when you create them. You can even store the state info in a database
and use the cookie as a key to retreive it.
When it comes to security, you cannot trust the contents of the cookie. The
contents need to be validated the same way the values from a form would be. A
tricky black hat can force the cookie contents to be anything they want.
Two last bits of advice from an old web developer (well as old as a web
developer can be).
Try to avoid frames. They cause a lot of problems for both you and for your
users. For example, they often break cross-browser, they can break bookmarks,
and they can break printing.
Try to avoid refreshes, especially frequent ones. Someone with a poor link
will spend more time looking at an empty page that hasn't loaded than they
will looking at your content.
> I hope i described the problem better now.
Don Garrett http://www.bgb.cc/garrett/
BGB Consulting garrett at bgb.cc
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