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Fix memory leak when duplicating too complex object

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[Bug #20162]

Creating a ST table then calling st_replace leaks memory because the
st_replace overwrites the ST table without freeing any of the existing
memory. This commit changes it to use st_copy instead.

For example:

    RubyVM::Shape.exhaust_shapes

    o = Object.new
    o.instance_variable_set(:@a, 0)

    10.times do
      100_000.times { o.dup }

      puts `ps -o rss= -p #{$$}`
    end

Before:

    23264
    33600
    42672
    52160
    61600
    71728
    81056
    90528
    100560
    109840

After:

    14752
    14816
    15584
    15584
    15664
    15664
    15664
    15664
    15664
    15664
This commit is contained in:
Peter Zhu 2024-01-08 11:32:48 -05:00
parent f165fa09e7
commit 82b57d7bfe
2 changed files with 14 additions and 2 deletions
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3
object.c
View File

@ -302,8 +302,7 @@ rb_obj_copy_ivar(VALUE dest, VALUE obj)
if (rb_shape_obj_too_complex(obj)) { if (rb_shape_obj_too_complex(obj)) {
// obj is TOO_COMPLEX so we can copy its iv_hash // obj is TOO_COMPLEX so we can copy its iv_hash
st_table * table = rb_st_init_numtable_with_size(rb_st_table_size(ROBJECT_IV_HASH(obj))); st_table *table = st_copy(ROBJECT_IV_HASH(obj));
st_replace(table, ROBJECT_IV_HASH(obj));
rb_obj_convert_to_too_complex(dest, table); rb_obj_convert_to_too_complex(dest, table);
return; return;

13
test/ruby/test_shapes.rb
View File

@ -942,6 +942,19 @@ class TestShapes < Test::Unit::TestCase
assert_shape_equal(RubyVM::Shape.of(obj), RubyVM::Shape.of(obj2)) assert_shape_equal(RubyVM::Shape.of(obj), RubyVM::Shape.of(obj2))
end end
def test_duplicating_too_complex_objects_memory_leak
assert_no_memory_leak([], "#{<<~'begin;'}", "#{<<~'end;'}", "[Bug #20162]", rss: true)
RubyVM::Shape.exhaust_shapes
o = Object.new
o.instance_variable_set(:@a, 0)
begin;
1_000_000.times do
o.dup
end
end;
end
def test_freezing_and_duplicating_object def test_freezing_and_duplicating_object
obj = Object.new.freeze obj = Object.new.freeze
obj2 = obj.dup obj2 = obj.dup