Performance update involving zval containers. Why not possible?

Hi,

first of all I want to say that I am just a newbie in PHP. I am
switching to PHP from other languages and I am exploring how PHP manages
references. To do that I am gathering information about what happens
with Symbol Tables and Variables Containers when using references. You
know: reference-counting, copy-on-write and all that stuff...

I found out some cases where I think that some Variable Containers
copies could be skipped, thus saving memory and improving performance
relying in the copy-on-write principle. I wrote a PDF trying to explain
what I mean. It is not written in a very techy language, because I am
just new and don't know too much about the internals, but I hope you can
understand it and post your comments.

Probably if my "update" hasn't been done yet, is because it is not
possible, but I will very glad to hear your comments and learn from you.

Thank you very much.

Pascal Chevrel wrote:

Le 20/09/2013 14:06, ruben a écrit :

Hi,

first of all I want to say that I am just a newbie in PHP. I am
switching to PHP from other languages and I am exploring how PHP manages
references. To do that I am gathering information about what happens
with Symbol Tables and Variables Containers when using references. You
know: reference-counting, copy-on-write and all that stuff...

I found out some cases where I think that some Variable Containers
copies could be skipped, thus saving memory and improving performance
relying in the copy-on-write principle. I wrote a PDF trying to explain
what I mean. It is not written in a very techy language, because I am
just new and don't know too much about the internals, but I hope you can
understand it and post your comments.

Probably if my "update" hasn't been done yet, is because it is not
possible, but I will very glad to hear your comments and learn from you.

Thank you very much.

Hi Ruben,

I think you forgot to put a link to your pdf :)

Regards,

Pascal

Sorry, here it is:
https://www.dropbox.com/s/wxdc99miw82zje9/PHP_references.pdf

Change the function to:
function & do_something(& $s) {

and it should do what you are expecting, reusing a single reference.

http://www.php.net/manual/en/language.references.return.php for more
reference.

I found out some cases where I think that some Variable Containers
copies could be skipped, thus saving memory and improving performance
relying in the copy-on-write principle. I wrote a PDF trying to explain
what I mean. It is not written in a very techy language, because I am
just new and don't know too much about the internals, but I hope you can
understand it and post your comments.

Sorry, here it is:
https://www.dropbox.com/s/wxdc99miw82zje9/PHP_references.pdf

Yes, in this simplified version there might be a way to figure this out
by doing special handling in the return handler (basically putting the
returned variable aside, do the cleanup and then see whether the
separation is still needed.

In most reference cases you will have other immediate calls and
operations in between which change the picture.

The general suggestion is: Don't use references, then the copy-on-write
can work in the most efficient way and really copy only when needed.
I've collected some thoughts about that on
http://schlueters.de/blog/archives/125-Do-not-use-PHP-references.html
Getting code with references right is hard and in 99% of the cases
(exceptions are in the area of circular graphs or algorithms working on
graphs ...while even there often using objects is better) other
approaches lead to faster and more maintainable code.

johannes