Hi Aaron Piotrowski,

> I would like to introduce an RFC for adding full-stack fibers to PHP: 
> https://wiki.php.net/rfc/fibers
>
> Fibers are primarily used to implement green-threads or coroutines for 
> asynchronous I/O. Fibers are similar to threads, except fibers exist within a 
> single thread and require cooperative scheduling of the fibers by the 
> process. Since fibers do not require a full CPU context switch, they are 
> lightweight and more performant than multi-processing or threading for 
> awaiting I/O.
>
> An implementation as an extension is at https://github.com/amphp/ext-fiber
>
> Fibers are a complex feature. The RFC contains many examples and links to 
> code using fibers to help explain and demonstrate what is possible, however 
> I’m certain many more questions and concerns will arise. Looking forward to 
> feedback and discussion.

I took a look at the amphp/ext-fiber repo a few weeks ago - nothing stood out 
as a major concern but I'm only moderately familiar with threading,
A minor comment is that it'd be easier to read the phpt test cases if the 
`--EXPECTF--`
section included the file's basename in the test output of error traces instead 
of just `%s`, etc.
(e.g. tests/002-throw.phpt)

```
Stack trace:
#0 %s(%d): {closure}()
#1 %s(%d): Loop->tick()
#2 %s(%d): Loop->run()
...
```

I didn't see in the test cases/rfc:
How do the `zend_try`/`zend_catch`/`zend_end_try` macros and 
`zend_error_noreturn` macros get handled after a fatal error?
I'm not 100% sure - I think those use setjmp/longjmp internally - will fatal 
errors continue to work if there's a fatal error from within a fiber.
(e.g. `require_once` on a file with a compile-time fatal error such as 
duplicate parameters).
I forget exactly how they work, e.g. in the context of a web server before this 
RFC - at a glance I'd guess an unrecoverable fatal error would cause the worker 
to shut down.
Would being in a different fiber and different C stack interfere with the 
shutdown process for fatal errors? (I guess the macros could be changed to make 
that switch to the main fiber if needed to fix that)

Thanks,
-Tyson Andre

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