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To: Larry Garfield <larry@garfieldtech.com>,
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Date: Mon, 23 Dec 2019 08:58:55 +0100
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Subject: Re: FFI, Preload, and performance
From: cmbecker69@gmx.de ("Christoph M. Becker")

On 20.12.2019 at 23:08, Larry Garfield wrote:

> The documentation doesn't really cover this, so I'm hoping it's OK to as=
k here.
>
> The FFI docs say that for web requests, you really really ought to use p=
reloading and then load/scope to manage an FFI library because it's going =
to be too slow to link up otherwise.  See the example here:
>
> https://www.php.net/manual/en/ffi.examples-complete.php
>
> What is unclear, though, is the performance impact of calling scope().  =
It happens at runtime in the example so I presume it's "fast enough" at ru=
ntime.  However, is it expected that it's only ever called once for a give=
n scope?  Or would it be safe to call multiple times in different places j=
ust to get an unshared reference to it?  Basically, would this be safe or =
a bad idea, and why?
>
>
> final class PrintProxy {
>     private static $ffi =3D null;
>     function __construct() {
>         if (is_null(self::$ffi)) {
>             self::$ffi =3D FFI::scope("DUMMY");
>         }
>     }
>     function printf($format, ...$args) {
>        return (int)self::$ffi->printf($format, ...$args);
>     }
> }
>
> final class SprintfProxy {
>     private static $ffi =3D null;
>     function __construct() {
>         if (is_null(self::$ffi)) {
>             self::$ffi =3D FFI::scope("DUMMY");
>         }
>     }
>     function printf($format, ...$args) {
>        return (string)self::$ffi->sprintf($format, ...$args);
>     }
> }
>
>
> The alternative being to have a single object that wraps scope("DUMMY") =
just once, and then inject that into both of those classes.  Is that worth=
 the extra hassle or no, and why?

=46rom looking at the implementation[1], FFI::scope() looks like a pretty
cheap operation; basically it's just looking up the scope from a
HashTable, and constructing a thin wrapper object around that.

But as always: when in doubt, measure! :)

[1]
<https://github.com/php/php-src/blob/php-7.4.1/ext/ffi/ffi.c#L3387-L3415>

=2D-
Christoph M. Becker