[Proposal] Idea for Application level variables

I noticed something which you said, and forgive me if this part may be
obvious, but you mentioned across instances of applications? Do you mean
something like a shared memory between all web connections to the
server? One issue I could forsee if this is the case, what happens when
there is no connections to the server for an extended period of time
(extended being even as short as a few minutes)? Should PHP store this
superglobal's value indefinitely, or perform some type of garbage
collection? If PHP should clean up after itself, what criteria would you
expect to be followed for deciding if something is no longer useful? I
don't think you would want this criteria configurable in a ini setting
for example, because hosting companies all do something different. If a
developer were to use this feature, they would need a standardized
timeframe that the values would last. This is just a couple things I
think would need to be considered before implementing something like
this. If I am way out in left field, I apologize.

-Jeremy

-----Original Message-----
From: Davey [mailto:davey@php.net]
Sent: Thursday, August 07, 2003 8:15 AM
To: internals@lists.php.net
Subject: Re: [PHP-DEV] [Proposal] Idea for Application level variables

Andrey,

// masv = my application shared vars. This is the name of the shared
var. > // Only the first 4 chars are used to calculate memory address.
$_APPLICATION = new Shm_Protected_Var("masv", 1024 /memory/); >
$_APPLICATION->start_section() > var_dump($_APPLICATION->getVal());
$_APPLICATION->end_section();

This isn't quite as transparent as $_SESSION is and $_APPLICATION would
also not be a superglobal. What I would like to see at the end of this
is a $_APPLICATION variable (or $_APP? some poeple complained that
$_APPLICATION is too long) that behaves exactly like $_SESSION (in
assignment etc) except that its values are available not across
sessions but across applications and instances of applications.

• Davey

Andrey Hristov wrote:

Hi Davey,
I don't know whether this will be implemented in an extension but
there are sollutions in userland : to use sysvshm+sysvsem or shmop.
The sysvshm+sysvsem extension exposes the C api. I know for 2 wrappers

around this API to make the use of shared memory (and thus something
like application wide variables) easy to implement in userspace:

http://www.php-tools.de/site.php?&PHPSESSID=b4a4ab7142b7d3209c7eee976912
0cba

&file=patMisc/shmc.xml
2)http://www.hristov.com/andrey/projects/php_stuff/shm.php.gz

The second one is written according to PEAR CS. It exposes 4 classes.
Shm_Protected_Var is what is needed to implement $_APPLICATION:

// masv = my application shared vars. This is the name of the shared
var. // Only the first 4 chars are used to calculate memory address.
$_APPLICATION = new Shm_Protected_Var("masv", 1024 /memory/);
$_APPLICATION->start_section() var_dump($_APPLICATION->getVal());
$_APPLICATION->end_section();

Regards,
Andrey

----- Original Message -----
From: "Davey" davey@php.net
To: internals@lists.php.net
Sent: Thursday, August 07, 2003 3:36 PM
Subject: [PHP-DEV] [Proposal] Idea for Application level variables

Hey,

I'm quite new to this, so please don't shoot this down too harshly. If
I don't explain something clearly enough, please ask me.

Because Application variables are pretty much shared session
variables, I wonder if perhaps the session code can be modified to
handle these variables.

In userland, the implementation would be similar to sessions, and can
work on two levels, for a single file or for a group of files.

Userland usage examples:

// cross file (i.e. an entire website)
application_vars_start('my_website'); // my_website is used as the SID

$_APPLICATION['website_users'] += 1;

// single file
application_vars_start(); // uses filename based SID, see below
$_APPLICATION['page_users'] += 1;

I figured that by using the following in place of the user-input SID,
you can easily have page-wide application vars, and by using the arg
for
application_var_start() in the the place of
SG(request_info).path_translated you can have it across whatever you
like, problem is when you have multiple sites on the same server,
someone else might choose the same name

PHP_MD5_CTX context;
PHP_MD5Init(&context);
PHP_MD5Update(&context, SG(request_info).path_translated,
strlen(SG(request_info).path_translated));
PHP_MD5Final(key, &context);

I don't know if this is clear enough, but in my head at least, it
seems a inexpensive solution to something PHP is (in some peoples
opinion) lacking. (Note: SRM seems like overkill just for this).

Another nice thing about this, as it'll be using the Session
infrastructure it could use the session handlers aswell (sqlite, mm
etc)

one problem that has been mentioned is multi-threaded situations, but
I would assume that either the current session code doesn't suffer
from this (and therefore neither will this) or that the session code
will need to be fixed itself anyways.

It should be noted that $_APPLICATION will not be affected during
run-time by other scripts changes, i.e. if a.php changes
$_APPLICATION['foo'] whilst b.php is running, it doesn't see the
changes till the next load... it might be nice to add a function to
force a reload of data in the current file though?

I'm not sure if you'd consider this to be implemented into the core,
but perhaps you could implement it into a PECL extension and then it
can be considered for core after it has had some real-life
testing/scenarios thrown at it?

Just to make it clear, I don't know C/C++ at all, this is just an idea
that you might or might not like to implement, I cannot do it (I had
help with the MD5 stuff ;).

• Davey