reuse open(2) from rb_file_load_ok on POSIX-like system

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.

1 files changed, 3 insertions, 0 deletions

diff --git a/internal/parse.h b/internal/parse.h
index f242c384ad..7cadd0cd5b 100644
--- a/internal/parse.h
+++ b/internal/parse.h
@@ -10,10 +10,13 @@
  */
 #include "ruby/ruby.h"          /* for VALUE */
 struct rb_iseq_struct;          /* in vm_core.h */
+struct ruby_file_load_state;    /* internal/file.h */
 
 /* parse.y */
 VALUE rb_parser_set_yydebug(VALUE, VALUE);
 void *rb_parser_load_file(VALUE parser, VALUE name);
+void *rb_parser_load_state(VALUE parser, VALUE name,
+                        struct ruby_file_load_state *);
 void rb_parser_keep_script_lines(VALUE vparser);
 void rb_parser_error_tolerant(VALUE vparser);
 void rb_parser_keep_tokens(VALUE vparser);