At 18:07 06/08/2001, Andrei Zmievski wrote:
>On Mon, 06 Aug 2001, Zeev Suraski wrote:
> > BTW, there's no good reason not to load all of the extensions you may need
> > in all of your scripts from php.ini.  Loading many extensions doesn't pose
> > a significant/noticeable load.  Loading using dl() does.
>Can you explain why the difference matters?

Sure.  dl() means that module_init is done multiple times.  It also means 
that module_shutdown is done multiple times, *and* has to take care of 
cleaning up after the extension *completely*.  That is, clean whatever 
functions, classes, ini entries and callbacks this function may have 
registered.  Right now, only PHP functions and ini entries (to a degree) 
are handled properly.

- It's slow.  We encourage putting expensive operations into the 
module_init, using dl() means they end up being done multiple times.

- Under Apache, it's even worse - since in addition to slowliness, it also 
ends up consuming significantly more memory, since any memory the extension 
allocates in module_init (e.g., the function entries it registers) cannot 
be shared between the processes.

- It prevents the engine from optimizing function calls at compile time, by 
looking at what kind of arguments these functions expect.  This is left for 
run-time, which results in significantly slower run-time performance.

- Literally, none of the extensions properly cleans up after itself, 
leaving PHP in various degrees of instability.  This rarely translates to 
crashes, because people don't usually have a script in which they dl() and 
then use a class, another script in which they use the class without 
dl()'ing first, and call the 2nd script right after calling the 1st 
one.  Still, from a cleanliness perspective and in theory, it's bad.

- Another buglet resulting from this is the crash in debug mode, in case of 
a memory leak inside an extension, which is reported in the bugs db.  It's 
no biggy, but also has no good solution.

I don't think the solution should be fixing all of the extensions to clean 
up after themselves, when the only gain is having dl() work, and when using 
dl() is almost always(*) significantly worse than simply adding the 
extension to the php.ini file.

(*) I can't think of any case in which it isn't, but I'm staying humble :)


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