[Bug #20342] Consider wrapped load in `main` methods

This reverts commit 6b73406833dd22e489114fa77c1c80c4b7af2ed0.

	Make io_fwrite safe for compaction

	[Bug #20169]

	Embedded strings are not safe for system calls without the GVL because
	compaction can cause pages to be locked causing the operation to fail
	with EFAULT. This commit changes io_fwrite to use rb_str_tmp_frozen_no_embed_acquire,
	which guarantees that the return string is not embedded.

	Don't pin named structs defined in Ruby

	[Bug #20311]

	`rb_define_class_under` assumes it's called from C and that the
	reference might be held in a C global variable, so it adds the
	class to the VM root.

	In the case of `Struct.new('Name')` it's wasteful and make
	the struct immortal.

	Make Struct memory leak test faster

	[Bug #20311]

	It times out on some platform, so we can reduce iterations.
	On my machine it completes in 250ms and RSS grows 8X.

The class variable cache that was added in
https://github.com/ruby/ruby/pull/4544 changed the behavior of class
variables on cloned classes. As reported when a class is cloned AND a
class variable was set, and the class variable was read from the
original class, reading a class variable from the cloned class would
return the value from the original class.

This was happening because the IC (inline cache) is stored on the ISEQ
which is shared between the original and cloned class, therefore they
share the cache too.

To fix this we are now storing the `cref` in the cache so that we can
check if it's equal to the current `cref`. If it's different we don't
want to read from the cache. If it's the same we do. Cloned classes
don't share the same cref with their original class.

This will need to be backported to 3.1 in addition to 3.2 since the bug
exists in both versions.

We also added a marking function which was missing.

Fixes [Bug #19379]

Co-authored-by: Aaron Patterson <tenderlove@ruby-lang.org>

	Fix indentation in vm_setivar_default

	---
	 vm_insnhelper.c | 6 +++---
	 1 file changed, 3 insertions(+), 3 deletions(-)

	[Bug #19469] Fix crash when resizing generic iv list

	The following script can sometimes trigger a crash:

	```ruby
	GC.stress = true

	class Array
	  def foo(bool)
	    if bool
	      @a = 1
	      @b = 2
	      @c = 1
	    else
	      @c = 1
	    end
	  end
	end

	obj = []
	obj.foo(true)

	obj2 = []
	obj2.foo(false)

	obj3 = []
	obj3.foo(true)
	```

	This is because vm_setivar_default calls rb_ensure_generic_iv_list_size
	to resize the iv list. However, the call to gen_ivtbl_resize reallocs
	the iv list, and then inserts into the generic iv table. If the
	st_insert triggers a GC then the old iv list will be read during
	marking, causing a use-after-free bug.

	Co-Authored-By: Jemma Issroff <jemmaissroff@gmail.com>
	---
	 internal/variable.h |  2 +-
	 variable.c          | 23 ++++++++++++++++++-----
	 vm_insnhelper.c     |  4 ++--
	 3 files changed, 21 insertions(+), 8 deletions(-)

	Only emit circular dependency warning for owned thread shields [Bug
	 #19415]

	If multiple threads attemps to load the same file concurrently
	it's not a circular dependency issue.

	So we check that the existing ThreadShield is owner by the current
	fiber before warning about circular dependencies.
	---
	 internal/thread.h                                     |  1 +
	 load.c                                                |  3 ++-
	 spec/ruby/core/kernel/shared/require.rb               | 11 +++++++++++
	 spec/ruby/fixtures/code/concurrent_require_fixture.rb |  4 ++++
	 test/ruby/test_require.rb                             |  3 ---
	 thread.c                                              | 11 +++++++++++
	 6 files changed, 29 insertions(+), 4 deletions(-)
	 create mode 100644 spec/ruby/fixtures/code/concurrent_require_fixture.rb

	Use Thread.pass until thread.stop? to wait for thread to block

	[Bug #19415]

	It should be more reliable
	---
	 spec/ruby/fixtures/code/concurrent_require_fixture.rb | 2 +-
	 1 file changed, 1 insertion(+), 1 deletion(-)

On a hash miss we need to call default if it is redefined in order to
return the default value to be used. Previously we checked this with
rb_method_basic_definition_p, which avoids the method call but requires
a method lookup.

This commit replaces the previous check with BASIC_OP_UNREDEFINED_P and
a new BOP_DEFAULT. We still need to fall back to
rb_method_basic_definition_p when called on a subclasss of hash.

    |                |compare-ruby|built-ruby|
    |:---------------|-----------:|---------:|
    |hash_aref_miss  |       2.692|     3.531|
    |                |           -|     1.31x|

Co-authored-by: Daniel Colson <danieljamescolson@gmail.com>
Co-authored-by: "Ian C. Anderson" <ian@iancanderson.com>
Co-authored-by: Jack McCracken <me@jackmc.xyz>

SIZE_POOL_COUNT is a GC macro, it should belong in gc.h and not shape.h.
SIZE_POOL_COUNT doesn't depend on shape.h so we can have shape.h depend
on gc.h.

Co-Authored-By: Matt Valentine-House <matt@eightbitraptor.com>

When an object becomes "too complex" (in other words it has too many
variations in the shape tree), we transition it to use a "too complex"
shape and use a hash for storing instance variables.

Without this patch, there were rare cases where shape tree growth could
"explode" and cause performance degradation on what would otherwise have
been cached fast paths.

This patch puts a limit on shape tree growth, and gracefully degrades in
the rare case where there could be a factorial growth in the shape tree.

For example:

```ruby
class NG; end

HUGE_NUMBER.times do
  NG.new.instance_variable_set(:"@unique_ivar_#{_1}", 1)
end
```

We consider objects to be "too complex" when the object's class has more
than SHAPE_MAX_VARIATIONS (currently 8) leaf nodes in the shape tree and
the object introduces a new variation (a new leaf node) associated with
that class.

For example, new variations on instances of the following class would be
considered "too complex" because those instances create more than 8
leaves in the shape tree:

```ruby
class Foo; end
9.times { Foo.new.instance_variable_set(":@uniq_#{_1}", 1) }
```

However, the following class is *not* too complex because it only has
one leaf in the shape tree:

```ruby
class Foo
  def initialize
    @a = @b = @c = @d = @e = @f = @g = @h = @i = nil
  end
end
9.times { Foo.new }
``

This case is rare, so we don't expect this change to impact performance
of most applications, but it needs to be handled.

Co-Authored-By: Aaron Patterson <tenderlove@ruby-lang.org>