From: xtkoba+ruby@... Date: 2021-06-14T01:24:32+00:00 Subject: [ruby-core:104257] [Ruby master Bug#17951] Collistions in Proc#hash values for blocks defined at the same line Issue #17951 has been updated by xtkoba (Tee KOBAYASHI). A possible fix: ```diff --- a/proc.c +++ b/proc.c @@ -1451,7 +1451,7 @@ rb_hash_proc(st_index_t hash, VALUE prc) GetProcPtr(prc, proc); hash = rb_hash_uint(hash, (st_index_t)proc->block.as.captured.code.val); hash = rb_hash_uint(hash, (st_index_t)proc->block.as.captured.self); - return rb_hash_uint(hash, (st_index_t)proc->block.as.captured.ep >> 16); + return rb_hash_uint(hash, (st_index_t)proc->block.as.captured.ep); } MJIT_FUNC_EXPORTED VALUE ``` I do not understand the meaning of the 16-bit right shift in the original code. ---------------------------------------- Bug #17951: Collistions in Proc#hash values for blocks defined at the same line https://bugs.ruby-lang.org/issues/17951#change-92436 * Author: decuplet (Nikita Shilnikov) * Status: Open * Priority: Normal * ruby -v: ruby 3.0.1p64 (2021-04-05 revision 0fb782ee38) [x86_64-darwin20] * Backport: 2.6: UNKNOWN, 2.7: UNKNOWN, 3.0: UNKNOWN ---------------------------------------- ```ruby require 'set' def capture(&block) block end # it creates 1k of same blocks blocks = Array.new(1000) { capture { :foo } } hashes = blocks.map(&:hash).uniq ids = blocks.map(&:object_id).uniq equality = blocks.map { blocks[0].eql?(_1) }.tally hash = blocks.to_h { [_1, nil] } set = blocks.to_set puts(hashes.size) # => 11 puts(ids.size) # => 1000 puts(equality.inspect) # => {true=>1, false=>999} puts(hash.size) # => 1000 puts(set.size) # => 1000 ``` The script builds one thousand blocks and then compares them in various ways. I would expect proc objects to be completely opaque and thus be treated as separate objects. As in, they are not equal. All tests but first confirm this expectation. However, `Proc#hash` doesn't return 1000 different results rather it varies between 3 and 20 on my machine. As I understand, current behavior doesn't violate ruby's guarantees. But I would expect `Proc#hash` results to be as unique as `Proc#object_id`, at least a lot more unique than they currently are. The problem is likely to occur only for blocks defined at the same line. ref to similar/related issue https://bugs.ruby-lang.org/issues/6048 -- https://bugs.ruby-lang.org/ Unsubscribe: