Implement GH-10854: TSRM should set a smarter value for expected_threads

[nielsdos]

Closes GH-10854

The tsrm_startup() function is currently always called with expected_threads = 1. This means that the hashtable used in the TSRM will only contain a single bucket, and all thread resources will therefore be in the same linked list. So it's not really a hashtable right now, even though it's supposed to be.

This patch adds a function tsrm_startup_ex() which takes the expected thread count as an argument. It also keeps the tsrm_startup() function so there are no BC breaks.

In the Apache SAPI we query how many threads we have, and pass that to the tsrm_startup_ex() function.

[iluuu1994]

Looks reasonable to me. I wonder if allocating a higher value "just in case" would make sense, as this allocation is unique and very small.

[nielsdos]

The current value should be the maximum number of threads per children. So I think that's good for the capacity of the hashtable.
Do you mean to increase it just to prevent collisions? In that case it's probably better if we choose the closest prime number >= the expected_threads count. But that would be something to implement in TSRM itself instead of Apache.

[iluuu1994]

I meant increasing it for the other SAPIs, but I don't know if that makes sense.

[nielsdos]

I checked the other SAPIs:

• CGI, CLI, PHPDBG: only run 1 thread, so nothing needs to change
• Fuzzer: not important to optimize the table, so nothing needs to change
• Embed: depends on the embedder, we could provide something in which they can configure it I guess, but maybe that's for another PR
• FPM: comment on top of file says it only runs in 1 thread, so nothing needs to change

So we only need to think some more about embed probably :-). I haven't spent time looking at that SAPI yet; and I think that would be for another PR.

[iluuu1994]

Right, so this looks fine then 🙂