The macro RCLASS_EXT() accesses the prime classext directly, but it can be
valid only in a limited situation when namespace is enabled.
So, to prevent using RCLASS_EXT() in the wrong way, rename the macro and
let the developer check it is ok to access the prime classext or not.
As well as `RB_OBJ_SHAPE_ID` -> `rb_obj_shape_id`
and `RSHAPE` is now a simple alias for `rb_shape_lookup`.
I tried to turn all these into `static inline` but I'm having
trouble with `RUBY_EXTERN rb_shape_tree_t *rb_shape_tree_ptr;`
not being exposed as I'd expect.
[Feature #15408]
Matz decided to deprecate it for Ruby 2.6 or 2.7 but that never
actually happened.
Given the object_id table is a contention point for Ractors
it seems sensible to finally deprecate this API so we can
generate and store object ids more efficiently in the future.
Use `st_foreach_with_replace` rather than to call `st_insert`
from inside `st_foreach`, this saves from having to disable GC.
Co-Authored-By: Peter Zhu <peter@peterzhu.ca>
And get rid of the `obj_to_id_tbl`
It's no longer needed, the `object_id` is now stored inline
in the object alongside instance variables.
We still need the inverse table in case `_id2ref` is invoked, but
we lazily build it by walking the heap if that happens.
The `object_id` concern is also no longer a GC implementation
concern, but a generic implementation.
Co-Authored-By: Matt Valentine-House <matt@eightbitraptor.com>
Ivars will longer be the only thing stored inline
via shapes, so keeping the `iv_index` and `ivptr` names
would be confusing.
Instance variables won't be the only thing stored inline
via shapes, so keeping the `ivptr` name would be confusing.
`field` encompass anything that can be stored in a VALUE array.
Similarly, `gen_ivtbl` becomes `gen_fields_tbl`.
This halves the amount of memory used for embedded RTypedData if they
are one VALUE (8 bytes on 64-bit platforms) over the slot size limit.
For Set, on 64-bit it uses an embedded 56-byte struct. With the
previous implementation, the embedded structs starts at offset 32,
resulting in a total size of 88. Since that is over the 80 byte
limit, it goes to the next highest bucket, 160 bytes, wasting 72
bytes. This allows it to fit in a 80 byte bucket, which reduces
the total size for small sets of from 224 bytes (160 bytes
embedded, 64 bytes malloc, 72 bytes wasted in embedding) to 144
bytes (80 bytes embedded, 64 bytes malloc, 0 bytes wasted in
embedding).
Any other embedded RTypedData will see similar advantages if they
are currently one VALUE over the limit.
To implement this, remove the typed_flag from struct RTypedData.
Embed the typed_flag information in the type member, which is
now a tagged pointer using VALUE type, using the bottom low 2 bits
as flags (1 bit for typed flag, the other for the embedded flag).
To get the actual pointer, RTYPEDDATA_TYPE masks out
the low 2 bits and then casts. That moves the RTypedData data
pointer from offset 32 to offset 24 (on 64-bit).
Vast amount of code in the internals (and probably external C
extensions) expects the following code to work for both RData and
non-embedded RTypedData:
```c
DATA_PTR(obj) = some_pointer;
```
Allow this to work by moving the data pointer in RData between
the dmark and dfree pointers, so it is at the same offset (24
on 64-bit).
Other than these changes to the include files, the only changes
needed were to gc.c, to account for the new struct layouts,
handle setting the low bits in the type member, and to use
RTYPEDDATA_TYPE(obj) instead of RTYPEDDATA(obj)->type.
This implements a hash set which is wait-free for lookup and lock-free
for insert (unless resizing) to use for fstring de-duplication.
As highlighted in https://bugs.ruby-lang.org/issues/19288, heavy use of
fstrings (frozen interned strings) can significantly reduce the
parallelism of Ractors.
I tried a few other approaches first: using an RWLock, striping a series
of RWlocks (partitioning the hash N-ways to reduce lock contention), and
putting a cache in front of it. All of these improved the situation, but
were unsatisfying as all still required locks for writes (and granular
locks are awkward, since we run the risk of needing to reach a vm
barrier) and this table is somewhat write-heavy.
My main reference for this was Cliff Click's talk on a lock free
hash-table for java https://www.youtube.com/watch?v=HJ-719EGIts. It
turns out this lock-free hash set is made easier to implement by a few
properties:
* We only need a hash set rather than a hash table (we only need keys,
not values), and so the full entry can be written as a single VALUE
* As a set we only need lookup/insert/delete, no update
* Delete is only run inside GC so does not need to be atomic (It could
be made concurrent)
* I use rb_vm_barrier for the (rare) table rebuilds (It could be made
concurrent) We VM lock (but don't require other threads to stop) for
table rebuilds, as those are rare
* The conservative garbage collector makes deferred replication easy,
using a T_DATA object
Another benefits of having a table specific to fstrings is that we
compare by value on lookup/insert, but by identity on delete, as we only
want to remove the exact string which is being freed. This is faster and
provides a second way to avoid the race condition in
https://bugs.ruby-lang.org/issues/21172.
This is a pretty standard open-addressing hash table with quadratic
probing. Similar to our existing st_table or id_table. Deletes (which
happen on GC) replace existing keys with a tombstone, which is the only
type of update which can occur. Tombstones are only cleared out on
resize.
Unlike st_table, the VALUEs are stored in the hash table itself
(st_table's bins) rather than as a compact index. This avoids an extra
pointer dereference and is possible because we don't need to preserve
insertion order. The table targets a load factor of 2 (it is enlarged
once it is half full).
This inverse table is only useful if `ObjectSpace._id2ref` is used,
which is extremely rare. The only notable exception is the `drb` gem
and even then it has an option not to rely on `_id2ref`.
So if we assume this table will never be looked up, we can just
not maintain it, and if it turns out `_id2ref` is called, we
can lock the VM and re-build it.
```
compare-ruby: ruby 3.5.0dev (2025-04-10T09:44:40Z master 684cfa42d7) +YJIT +PRISM [arm64-darwin24]
built-ruby: ruby 3.5.0dev (2025-04-10T10:13:43Z lazy-id-to-obj d3aa9626cc) +YJIT +PRISM [arm64-darwin24]
warming up..
| |compare-ruby|built-ruby|
|:----------|-----------:|---------:|
|baseline | 26.364M| 25.974M|
| | 1.01x| -|
|object_id | 10.293M| 14.202M|
| | -| 1.38x|
```
Using `rb_obj_clone` introduce other problems, such as `initialize_*`
callbacks invocation in the context of the parent ractor.
So we can revert back to copy the content of the object slots,
but in a way that is aware of size pools.
[Bug #20271]
[Bug #20267]
[Bug #20255]
`rb_obj_alloc(RBASIC_CLASS(obj))` will always allocate from the basic
40B pool, so if `obj` is larger than `40B`, we'll create a corrupted
object when we later copy the shape_id.
Instead we can use the same logic than ractor copy, which is
to use `rb_obj_clone`, and later ask the GC to free the original
object.
We then must turn it into a `T_OBJECT`, because otherwise
just changing its class to `RactorMoved` leaves a lot of
ways to keep using the object, e.g.:
```
a = [1, 2, 3]
Ractor.new{}.send(a, move: true)
[].concat(a) # Should raise, but wasn't.
```
If it turns out that `rb_obj_clone` isn't performant enough
for some uses, we can always have carefully crafted specialized
paths for the types that would benefit from it.
This function replaces the internal rb_obj_gc_flags API. rb_gc_object_metadata
returns an array of name and value pairs, with the last element having
0 for the name.
We should skip reference updating for entries in too complex generic ivars
that are special constants. This fixes the following crash:
MAX_SHAPES = 0x80000
MAX_SHAPES.times do |i|
o = []
o.instance_variable_set(:"@foo#{i}", 1)
end
o = []
o.instance_variable_set(:"@a", 123)
GC.compact
The `ids` array and `dsymbol_fstr_hash` were pinned because they were
kept alive by rb_vm_register_global_object. This prevented the GC from
moving them even though there were reference updating code.
This commit changes it to be marked movable by marking it as a root object.
When the Ractor list is not initialized and a GC is ran at boot, then it
would crash because the newobj_cache of the main Ractor is not cleared.
This commit changes it to use ruby_single_main_ractor when it's available
and iterate over the Ractor list when we have multiple Ractors.
For moving garbage collectors, we may want to combine liveliness checking
with reference updating for performance. This commit allows for non-weak
references to be passed into the callback function when weak_only is false.
Previously, generic ivars worked differently than the other global tables
during compaction. The other global tables had their references updated
through iteration during rb_gc_update_vm_references. Generic ivars updated
the keys when the object moved and updated the values while reference
updating the object. This is inefficient as this required one lookup for
every moved object and one lookup for every object with generic ivars.
Instead, this commit changes it to iterate over the generic ivar table to
update both the keys and values.
We must disable GC when running RUBY_INTERNAL_EVENT_NEWOBJ hooks because
the callback could call xmalloc which could potentially trigger a GC,
and a lot of code is unsafe to trigger a GC right after an object has
been allocated because they perform initialization for the object and
assume that the GC does not trigger before then.
