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ruby--ruby/test/-ext-/string/test_rb_str_dup.rb

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str_duplicate: Don't share with a frozen shared string This is a follow up for 3f9562015e651735bfc2fdd14e8f6963b673e22a. Before this commit, it was possible to create a shared string which shares with another shared string by passing a frozen shared string to `str_duplicate`. Such string looks like: ``` -------- ----------------- | root | ------ owns -----> | root's buffer | -------- ----------------- ^ ^ ^ ----------- | | | shared1 | ------ references ----- | ----------- | ^ | ----------- | | shared2 | ------ references --------- ----------- ``` This is bad news because `rb_fstring(shared2)` can make `shared1` independent, which severs the reference from `shared1` to `root`: ```c /* from fstr_update_callback() */ str = str_new_frozen(rb_cString, shared2); /* can return shared1 */ if (STR_SHARED_P(str)) { /* shared1 is also a shared string */ str_make_independent(str); /* no frozen check */ } ``` If `shared1` was the only reference to `root`, then `root` can be reclaimed by the GC, leaving `shared2` in a corrupted state: ``` ----------- -------------------- | shared1 | -------- owns --------> | shared1's buffer | ----------- -------------------- ^ | ----------- ------------------------- | shared2 | ------ references ----> | root's buffer (freed) | ----------- ------------------------- ``` Here is a reproduction script for the situation this commit fixes. ```ruby a = ('a' * 24).strip.freeze.strip -a p a 4.times { GC.start } p a ``` - string.c (str_duplicate): always share with the root string when the original is a shared string. - test_rb_str_dup.rb: specifically test `rb_str_dup` to make sure it does not try to share with a shared string. [Bug #15792] Closes: https://github.com/ruby/ruby/pull/2159
2019-05-08 09:44:41 -04:00
require 'test/unit'
require '-test-/string'
class Test_RbStrDup < Test::Unit::TestCase
def test_nested_shared_non_frozen
str = Bug::String.rb_str_dup(Bug::String.rb_str_dup("a" * 50))
assert_send([Bug::String, :shared_string?, str])
assert_not_send([Bug::String, :sharing_with_shared?, str], '[Bug #15792]')
end
def test_nested_shared_frozen
str = Bug::String.rb_str_dup(Bug::String.rb_str_dup("a" * 50).freeze)
assert_send([Bug::String, :shared_string?, str])
assert_not_send([Bug::String, :sharing_with_shared?, str], '[Bug #15792]')
end
end
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