On Wednesday 25 October 2006 14:48, Jon Anderson wrote:
> Take this with a grain of salt. I develop with PHP, but I am not an
> internals guy...
>
> jeff.phplist@xxxxxxxxxxxx wrote:
> > Are the include files only compiled when execution hits them, or are
> > all include files compiled when the script is first compiled, which
> > would mean a cascade through all statically linked include files. By
> > statically linked files I mean ones like "include ('bob.php')" - i.e
> > the filename isn't in a variable.
>
> Compiled when execution hits them. You can prove this by trying to
> conditionally include a file with a syntax error: if (false)
> include('script_with_syntax_error.php'); won't cause an error.
>
> > Secondly, are include files that are referenced, but not used, loaded
> > into memory? I.e Are statically included files automatically loaded
> > into memory at the start of a request? (Of course those where the name
> > is variable can only be loaded once the name has been determined.) And
> > when are they loaded into memory? When the instruction pointer hits
> > the include? Or when the script is initially loaded?
>
> If your include file is actually included, it will use memory. If it is
> not included because of some condition, then it won't use memory.
>
> > Are included files ever unloaded? For instance if I had 3 include
> > files and no loops, once execution had passed from the first include
> > file to the second, the engine might be able to unload the first file.
> > Or at least the code, if not the data.
>
> If you define a global variable in an included file and don't unset it
> anywhere, then it isn't automatically "unloaded", nor are function/class
> definitions unloaded when execution is finished.
>
> Once you include a file, it isn't unloaded later though - even included
> files that have just executed statements (no definitions saved for
> later) seem to eat a little memory once, but it's so minimal that you
> wouldn't run into problems unless you were including many thousand
> files. Including the same file again doesn't eat further memory. I
> assume the eaten memory is for something to do with compilation or
> caching in the ZE.
>
> > Thirdly, I understand that when a request arrives, the script it
> > requests is compiled before execution. Now suppose a second request
> > arrives for the same script, from a different requester, am I right in
> > assuming that the uncompiled form is loaded? I.e the script is
> > tokenized for each request, and the compiled version is not loaded
> > unless you have engine level caching installed - e.g. MMCache or Zend
> > Optimiser.
>
> I think that's correct. If you don't have an opcode cache, the script is
> compiled again for every request, regardless of who requests it.
>
> IMO, you're probably better off with PECL/APC or eAccelerator rather
> than MMCache or Zend Optimizer. I use APC personally, and find it
> exceptional -> rock solid + fast. (eAccelerator had a slight performance
> edge for my app up until APC's most recent release, where APC now has a
> significant edge.)
>
> > Fourthly, am I right in understanding that scripts do NOT share
> > Fifthly, if a script takes 4MB, given point 4, does the webserver
> > demand 8MB if it is simultaneously servicing 2 requests?
>
> Yep. More usually with webserver/PHP overhead.
Unless you're using an opcode cache, as I believe some of the are smarter
about that. Which and how, I don't know. :-)
--
Larry Garfield AIM: LOLG42
larry@xxxxxxxxxxxxxxxx ICQ: 6817012
"If nature has made any one thing less susceptible than all others of
exclusive property, it is the action of the thinking power called an idea,
which an individual may exclusively possess as long as he keeps it to
himself; but the moment it is divulged, it forces itself into the possession
of every one, and the receiver cannot dispossess himself of it." -- Thomas
Jefferson
--
PHP General Mailing List (http://www.php.net/)
To unsubscribe, visit: http://www.php.net/unsub.php
