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, 23 insertions, 0 deletions

diff --git a/ruby.c b/ruby.c
index 8287869d20..f7d0238173 100644
--- a/ruby.c
+++ b/ruby.c
@@ -2539,6 +2539,29 @@ rb_parser_load_file(VALUE parser, VALUE fname_v)
     return load_file(parser, fname_v, f, 0, &opt);
 }
 
+void *
+rb_parser_load_state(VALUE parser, VALUE fname_v,
+                     struct ruby_file_load_state *fls)
+{
+    if (fls->filev != Qfalse) {
+        ruby_cmdline_options_t opt;
+
+        cmdline_options_init(&opt);
+        /* TODO: xflag for DOSISH || __CYGWIN__ */
+        if (fls->is_nonblock) {
+            struct rb_io_t *fptr;
+
+            RB_IO_POINTER(fls->filev, fptr);
+            disable_nonblock(fptr->fd);
+        }
+        if (fls->is_fifo) {
+            rb_io_wait(fls->filev, RB_INT2NUM(RUBY_IO_READABLE), Qnil);
+        }
+        return load_file(parser, fname_v, fls->filev, 0, &opt);
+    }
+    return rb_parser_load_file(parser, fname_v);
+}
+
 /*
  *  call-seq:
  *     Process.argv0  -> frozen_string