From: naruse@...
Date: 2017-04-18T09:14:21+00:00
Subject: [ruby-core:80763] [Ruby trunk Feature#13434] better method	definition in C API

Issue #13434 has been updated by naruse (Yui NARUSE).


I agree with the concept.

From r55102, rb_scan_args is statically resolved by C compilers on some environment, rb_get_kwargs is still inefficient.
To allow C compilers statically resolve them, Ruby method in C should be defined in more machine friendly way.

I thought the new API should use C struct (write rb_method_info by hand?).
Anyway we should list up the requirement of the new API, for example
* readonly/unused flag for arguments.
* whether the caller requires return single value, multiple value (like Perl's wantarray), or not.

----------------------------------------
Feature #13434: better method definition in C API
https://bugs.ruby-lang.org/issues/13434#change-64351

* Author: normalperson (Eric Wong)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
Current ways to define and parse arguments in the Ruby C API are clumsy,
slow, and impede potential optimizations.

The current C API for defining (rb_define_{singleton_}, method),
and parsing (rb_scan_args, rb_get_kwargs) is orthogonal but inefficient.

rb_get_kwargs creates garbage which pure Ruby kwarg methods do not.
[Feature #11339] was an ugly workaround to use Ruby wrapper methods
for IO#*nonblock methods to avoid garbage from rb_get_kwargs.

Furthermore, it should be possible to annotate args for C functions as
"read-only, use-once" or similar.  In other words, it should be possible to
implement my idea from [ruby-core:80626] where method lookup can be done
out-of-order in some cases, and allow optimizations such as replacing
"putstring" insns with garbage-free "putobject" insns for constants strings
without introducing backwards incompatibility for Rubyists.

We can also get rid of the limited basic op redefinition checks and
implement more generic versions of opt_aref_with / opt_aset_with
for more functions that can take frozen string args.

The "read-only, use-once" annotation can even make it safe for
a dynamic strings to be immediately recycled to reduce garbage.

So we could annotate "puts" and IO#write in a way that causes the VM to
immediately recycle its argument if it's a dynamically-generated string:

	puts "#{dynamic} #{string(:here)}"

I am not good at API design; so I'm not sure what it should look like.

Perhaps sendmsg_nonblock may be implemented like:

```
struct rb_method_info {
    /* to be filled in by rb_def_method ... */
};

static VALUE
sendmsg_nonblock(struct rb_method_info *info, int argc, VALUE *argv, VALUE self)
{
    VALUE mesg, flags, dest_sockaddr, control, exception;

    rb_get_args(info, argc, argv,
		&mesg, &flags, &dest_sockaddr, &control, &exception);

    ...
}

/*
 * ALLCAPS variable names mean read-only (like "constants" in Ruby)
 * "1" prefix means use only once, eligible for immediately recycle
 * if dynamic string
 */

rb_def_method(rb_cBasickSocket, sendmsg_nonblock,
              "sendmsg_nonblock(1MESG "
				"1FLAGS = 0), "
				"1DEST_SOCKADDR = nil), "
				"*1CONTROL, exception: true)", -1);

/* rb_hash_aset can be done as:
 * where 0KEY (not "1" prefix) means it is constant and persistent,
 * and "val" (all lower case, no prefix) means it is a normal
 * variable which can persistent after the function returns
 */
rb_def_method(rb_Hash, rb_hash_aset, "[0KEY]=val", 2);
```

Thoughts?

The existing C API must continue to work, so 3rd-party extensions can
migrate to the new API slowly.




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