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Make inline cache reads / writes atomic with object shapes

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Prior to this commit, we were reading and writing ivar index and
shape ID in inline caches in two separate instructions when
getting and setting ivars. This meant there was a race condition
with ractors and these caches where one ractor could change
a value in the cache while another was still reading from it.

This commit instead reads and writes shape ID and ivar index to
inline caches atomically so there is no longer a race condition.

Co-Authored-By: Aaron Patterson <tenderlove@ruby-lang.org>
Co-Authored-By: John Hawthorn <john@hawthorn.email>
This commit is contained in:
Jemma Issroff 2022-10-03 13:52:40 -04:00 • committed by Aaron Patterson
parent ad63b668e2
commit 913979bede
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GPG key ID: 953170BCB4FFAFC6
13 changed files with 222 additions and 244 deletions
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6
variable.c
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@ -1627,7 +1627,7 @@ iterate_over_shapes_with_callback(rb_shape_t *shape, VALUE* iv_list, rb_ivar_for
case SHAPE_ROOT:
return;
case SHAPE_IVAR:
iterate_over_shapes_with_callback(shape->parent, iv_list, callback, arg);
iterate_over_shapes_with_callback(rb_shape_get_shape_by_id(shape->parent_id), iv_list, callback, arg);
VALUE val = iv_list[shape->iv_count - 1];
if (val != Qundef) {
callback(shape->edge_name, val, arg);
@ -1635,7 +1635,7 @@ iterate_over_shapes_with_callback(rb_shape_t *shape, VALUE* iv_list, rb_ivar_for
return;
case SHAPE_IVAR_UNDEF:
case SHAPE_FROZEN:
iterate_over_shapes_with_callback(shape->parent, iv_list, callback, arg);
iterate_over_shapes_with_callback(rb_shape_get_shape_by_id(shape->parent_id), iv_list, callback, arg);
return;
}
}
@ -1694,7 +1694,7 @@ rb_copy_generic_ivar(VALUE clone, VALUE obj)
rb_shape_t * obj_shape = rb_shape_get_shape(obj);
if (rb_shape_frozen_shape_p(obj_shape)) {
rb_shape_set_shape(clone, obj_shape->parent);
rb_shape_set_shape_id(clone, obj_shape->parent_id);
}
else {
rb_shape_set_shape(clone, obj_shape);