perf: only import os environment variables once per worker thread

[AlliBalliBaba]

I noticed that php_import_environment_variables will lock and increasingly slow down the server as more environment variables are imported.
Since many frameworks will cache environment variables in production, the import often ends up being redundant. I think it would make sense to only import them once per thread, at least in worker mode.

Some open points:

• How do other SAPIs optimize this? (not yet sure what exactly's happening here: litespeed fpm )
• Should this be an optional configuration in the Caddyfile?
• Should this also be possible in non-worker mode?

Here is a graph showing that the server slows down with an increasing amount of environment variables .
When we load the environment from a zval that's cached on the thread, the slowdown is much less significant:

the env variables have ~40 characters each
Note that 10 threads is the 'ideal' amount of threads on my 20 core machine when PHP does minimal work

[AlliBalliBaba]

worker without caching (~20 env variables)

worker with caching (~20 env variables)

[AlliBalliBaba]

Leak should be fixed. I think caching the os environment is the expected default for worker mode. I can add it as optional to the Caddy config though

[dunglas]

I'm in favor of both adding this cache (without an option to disable it) to mimick the FPM behavior and merging #1086.

Very good work again!

[dunglas]

Can we merge this one?

[AlliBalliBaba]

I think we can probably merge this. Super-globals (or auto_globals) still have some weirdness about them that I'm trying to understand. Their ->jit mechanism to only load when they are being accessed doesn't restore itself when they are destroyed (more specifically this is true for $_SERVER). But that's probably something for a different PR.

[dunglas]

Thank you!