[ruby-core:112620] [Ruby master Feature#19465] [PATCH] reuse open(2) from rb_file_load_ok on POSIX-like system

Issue #19465 has been updated by k0kubun (Takashi Kokubun).

Status changed from Closed to Assigned
Assignee set to normalperson (Eric Wong)

Since there has been no action since @hsbt reported it, I temporarily reverted the commit at commit:526111290b2e01e798f436dfe4acc3bf10c6bbd1. Please have a look at the failure and re-push it once the issue is resolved. Thank you!

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Feature #19465: [PATCH] reuse open(2) from rb_file_load_ok on POSIX-like system
https://bugs.ruby-lang.org/issues/19465#change-102068

* Author: normalperson (Eric Wong)
* Status: Assigned
* Priority: Normal
* Assignee: normalperson (Eric Wong)
----------------------------------------
```
When loading Ruby source files, we can save the result of
successful opens as open(2)/openat(2) are a fairly expensive
syscalls.  This also avoids a time-of-check-to-time-of-use
(TOCTTOU) problem.

This reduces open(2) syscalls during `require'; but should be
most apparent when users have a small $LOAD_PATH.  Users with
large $LOAD_PATH will benefit less since there'll be more
open(2) failures due to ENOENT.

With `strace -c -e openat ruby -e exit' under Linux, this
results in a ~14% reduction of openat(2) syscalls
(glibc uses openat(2) to implement open(2)).

 % time     seconds  usecs/call     calls    errors syscall
 ------ ----------- ----------- --------- --------- ----------------
   0.00    0.000000           0       296       110 openat
   0.00    0.000000           0       254       110 openat

Additionally, the introduction of `struct ruby_file_load_state'
may make future optimizations more apparent.

This change cannot benefit binary (.so) loading since the
dlopen(3) API requires a filename and I'm not aware of an
alternative that takes a pre-existing FD.  In typical
situations, Ruby source files outnumber the mount of .so
files.


I've only tested this lightly on small apps since I don't have
large codebases to test on.  However, I think organizing various
on-stack variables into `struct ruby_file_load_state' can be
beneficial if we end up using io-uring on Linux.
```


---Files--------------------------------
0001-reuse-open-2-from-rb_file_load_ok-on-POSIX-like-syst.patch (15.2 KB)


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