This patch lazily allocates id tables for shape children. If a shape
has only one single child, it tags the child with a bit. When we read
children, if the id table has the bit set, we know it's a single child.
If we need to add more children, then we create a new table and evacuate
the child to the new table.
Co-Authored-By: Matt Valentine-House <matt@eightbitraptor.com>
We can only allocate enough shapes to fit in the shape buffer.
MAX_SHAPE_ID was based on the theoretical maximum number of shapes we
could have, not on the amount of memory we can actually consume. This
commit changes the MAX_SHAPE_ID to be based on the amount of memory
we're allowed to consume.
Co-Authored-By: Jemma Issroff <jemmaissroff@gmail.com>
[Bug #19536]
When objects are moved between size pools, their frozen status is lost
in the shape. This will cause the frozen check to be bypassed when there
is an inline cache. For example, the following script should raise a
FrozenError, but doesn't on Ruby 3.2 and master.
class A
def add_ivars
@a = @b = @c = @d = 1
end
def set_a
@a = 10
end
end
a = A.new
a.add_ivars
a.freeze
b = A.new
b.add_ivars
b.set_a # Set the inline cache in set_a
GC.verify_compaction_references(expand_heap: true, toward: :empty)
a.set_a
This makes the behavior of classes and modules when there are too many instance variables match the behavior of objects with too many instance variables.
Create SHAPE_MAX_NUM_IVS (currently 50) and limit all shapes of
T_OBJECTS to that number of IVs. When a shape with a T_OBJECT has more than 50 IVs, fall back to the
obj_too_complex shape which uses hash lookup for ivs.
Note that a previous version of this commit
78fcc9847a was reverted in
88f2b94065 because it did not account for
non-T_OBJECTS
Create SHAPE_MAX_NUM_IVS (currently 50) and limit all shapes to that
number of IVs. When a shape has more than 50 IVs, fallback to the
obj_too_complex shape which uses hash lookup for ivs.
Under strict aliasing, writing to the memory location of a different
type is not allowed and will result in undefined behavior. This was
happening in shape.c due to `rb_id_table_lookup` writing to the memory
location of `VALUE *` that was casted from a `rb_shape_t **`.
This was causing test failures when compiled with LTO.
Fixes [Bug #19248]
Co-Authored-By: Alan Wu <alanwu@ruby-lang.org>
RubyVM::Shape is usually not available (you need SHAPE_DEBUG macro,
which is not defined by default). So it seems confusing to leave
RubyVM::Shape in the document.
This hides only method definitions because, well, I can't find a way to
hide things defined by rb_define_const or rb_struct_define_under. I gave
up making the C-based documentation right. You should define things in
Ruby instead.
Make printing shapes better, use a struct instead of specific methods
for each field on a shape.
Co-Authored-By: Aaron Patterson <tenderlove@ruby-lang.org>
When moving Objects between size pools we have to assign a new shape.
This happened during updating references - we tried to create a new shape
tree that mirrored the existing tree, but based on the root shape of the
new size pool.
This causes allocations to happen if the new tree doesn't already exist,
potentially triggering a GC, during GC.
This commit changes object movement to look for a pre-existing new tree
during object movement, and if that tree does not exist, we don't move
the object to the new pool.
This allows us to remove the shape allocation from update references.
Co-Authored-By: Peter Zhu <peter@peterzhu.ca>
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>
Count how many "variations" each class creates. A "variation" is a a
unique ordering of instance variables on a particular class. This can
also be thought of as a branch in the shape tree.
For example, the following Foo class will have 2 variations:
```ruby
class Foo ; end
Foo.new.instance_variable_set(:@a, 1) # case 1: creates one variation
Foo.new.instance_variable_set(:@b, 1) # case 2: creates another variation
foo = Foo.new
foo.instance_variable_set(:@a, 1) # does not create a new variation
foo.instance_variable_set(:@b, 1) # does not create a new variation (a continuation of the variation in case 1)
```
We will use this number to limit the amount of shapes that a class can
create and fallback to using a hash iv lookup.
Co-Authored-By: Aaron Patterson <tenderlove@ruby-lang.org>
When moving Objects between size pools we have to assign a new shape.
This happened during updating references - we tried to create a new shape
tree that mirrored the existing tree, but based on the root shape of the
new size pool.
This causes allocations to happen if the new tree doesn't already exist,
potentially triggering a GC, during GC.
This commit changes object movement to look for a pre-existing new tree
during object movement, and if that tree does not exist, we don't move
the object to the new pool.
This allows us to remove the shape allocation from update references.
Co-Authored-By: Peter Zhu <peter@peterzhu.ca>
Since edc7af48ac, we now no longer have
undef ivar transitions. Instead, we rebuild the shapes table. When we do
this, we need to ensure that we retain our capacities on shapes.
I see several arguments in doing so.
First they use a non trivial amount of memory, so for various memory
profiling/mapping tools it is relevant to have visibility of the space
occupied by shapes.
Then, some pathological code can create a tons of shape, so it is
valuable to have a way to have a way to observe shapes without having
to compile Ruby with `SHAPE_DEBUG=1`.
And additionally it's likely much faster to dump then this way than
to use `RubyVM::Shape`.
There are however a few open questions:
- Shapes can't respect the `since:` argument. Not sure what to do when
it is provided. Would probably make sense to not dump them.
- Maybe it would make more sense to have a separate `ObjectSpace.dump_shapes`?
- Maybe instead `dump_all` should take a `shapes: false` argument?
Additionally, `ObjectSpace.dump_shapes` is added for the use case of
debugging the evolution of the shape tree.
Cases like this:
```ruby
obj = Object.new
loop do
obj.instance_variable_set(:@foo, 1)
obj.remove_instance_variable(:@foo)
end
```
can cause us to use many more shapes than we want (and even run out).
This commit changes the code such that when an instance variable is
removed, we'll walk up the shape tree, find the shape, then rebuild any
child nodes that happened to be below the "targetted for removal" IV.
This also requires moving any instance variables so that indexes derived
from the shape tree will work correctly.
Co-Authored-By: Jemma Issroff <jemmaissroff@gmail.com>
Co-authored-by: John Hawthorn <jhawthorn@github.com>
This commit significantly speeds up shape transitions as it changes
get_next_shape_internal to not perform a lookup (and instead require
the caller to perform the lookup). This avoids double lookups during
shape transitions.
There is a significant (~2x) speedup in the following micro-benchmark:
puts(Benchmark.measure do
o = Object.new
100_000.times do |i|
o.instance_variable_set(:"@a#{i}", 0)
end
end)
Before:
22.393194 0.201639 22.594833 ( 22.684237)
After:
11.323086 0.022284 11.345370 ( 11.389346)
We would like to differentiate types of objects via their shape. This
commit adds a special T_OBJECT shape when we allocate an instance of
T_OBJECT. This allows us to avoid testing whether an object is an
instance of a T_OBJECT or not, we can just check the shape.
In rb_shape_rebuild_shape, we need to increase the capacity when
capacity == next_iv_index since the next ivar will be writing at index
next_iv_index.
This bug can be reproduced when assertions are turned on and you run the
following code:
class Foo
def initialize
@a1 = 1
@a2 = 1
@a3 = 1
@a4 = 1
@a5 = 1
@a6 = 1
@a7 = 1
end
def add_ivars
@a8 = 1
@a9 = 1
end
end
class Bar < Foo
end
foo = Foo.new
foo.add_ivars
bar = Bar.new
GC.start
bar.add_ivars
bar.clone
You will get the following crash:
Assertion Failed: object.c:301:rb_obj_copy_ivar:src_num_ivs <= shape_to_set_on_dest->capacity
This commit adds a `capacity` field to shapes, and adds shape
transitions whenever an object's capacity changes. Objects which are
allocated out of a bigger size pool will also make a transition from the
root shape to the shape with the correct capacity for their size pool
when they are allocated.
This commit will allow us to remove numiv from objects completely, and
will also mean we can guarantee that if two objects share shapes, their
IVs are in the same positions (an embedded and extended object cannot
share shapes). This will enable us to implement ivar sets in YJIT using
object shapes.
Co-Authored-By: Aaron Patterson <tenderlove@ruby-lang.org>
* Avoid RCLASS_IV_TBL in marshal.c
* Avoid RCLASS_IV_TBL for class names
* Avoid RCLASS_IV_TBL for autoload
* Avoid RCLASS_IV_TBL for class variables
* Avoid copying RCLASS_IV_TBL onto ICLASSes
* Use object shapes for Class and Module IVs
`iv_count` is a misleading name because when IVs are unset, the new
shape doesn't decrement this value. `next_iv_count` is an accurate, and
more descriptive name.
Shape IDs are unsigned. This commit unwraps the shape id as an unsigned
int, which will automatically raise an argument error and also eliminate
a compilation warning.
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>
Aaron Patterson
Peter Zhu
HParker
Takashi Kokubun
Haldun Bayhantopcu
Matt Valentine-House
Jemma Issroff
Jean Boussier
John Hawthorn
Nobuyoshi Nakada