Issue #20608 has been updated by mame (Yusuke Endoh). As you've probably noticed from reading the source, there is no `Hash#find` method. `Enumerable#find` is. It cannot know that `#each` yields a two-element array, so it is not easy to optimize it. We could define Hash#find method as a faster special version of Enumerable#find. I personally don't like the idea of manually copying many Enumerable methods into Hash... I was rather surprised that there is a `Hash#any?`. Even though there is no `Hash#all?`. If the consistency is an issue, a simple fix to this "bug" would be to remove `Hash#any?`. ---------------------------------------- Bug #20608: Hash#find always allocates each iterated pair https://bugs.ruby-lang.org/issues/20608#change-108961 * Author: ivoanjo (Ivo Anjo) * Status: Open * ruby -v: ruby 3.4.0preview1 (2024-05-16 master 9d69619623) [x86_64-linux] * Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN ---------------------------------------- Hey there! Recently I ran into this sharp edge in `Hash#find`: ```ruby puts RUBY_DESCRIPTION def allocated_now = GC.stat(:total_allocated_objects) dummy_hash = 10_000.times.each_with_index.to_h before_allocs = allocated_now dummy_hash.any? { |k, v| } puts "Allocated #{allocated_now - before_allocs} for #{File.read(__FILE__).lines[__LINE__-2]}" before_allocs = allocated_now dummy_hash.each { |k, v| } puts "Allocated #{allocated_now - before_allocs} for #{File.read(__FILE__).lines[__LINE__-2]}" before_allocs = allocated_now dummy_hash.find { |k, v| } puts "Allocated #{allocated_now - before_allocs} for #{File.read(__FILE__).lines[__LINE__-2]}" before_allocs = allocated_now dummy_hash.any? { |k| } puts "Allocated #{allocated_now - before_allocs} for #{File.read(__FILE__).lines[__LINE__-2]}" ``` Result: ``` ruby 3.4.0preview1 (2024-05-16 master 9d69619623) [x86_64-linux] Allocated 0 for dummy_hash.any? { |k, v| } Allocated 0 for dummy_hash.each { |k, v| } Allocated 10002 for dummy_hash.find { |k, v| } Allocated 10000 for dummy_hash.any? { |k| } ``` That is, while `Hash#any?`, `Hash#each`, etc avoid doing any allocations during iteration, `Hash#find` does not hit the `rb_block_pair_yield_optimizable` => `each_pair_i_fast` fast path, and so is massively costly compared to the others. This is very surprising, as I'd expect a `find` to have a comparable cost to `any?` (and I ended up [redoing some code to avoid find](https://github.com/DataDog/dd-trace-rb/pull/3757)). Also while experimenting a bit, it was surprising to me that the allocation optimization only kicks in when `|k, v|` are declared, and thus `.any? { |k| }` is also more expensive. -- https://bugs.ruby-lang.org/

Issue #20608 has been updated by mame (Yusuke Endoh). Assignee set to ko1 (Koichi Sasada) Status changed from Open to Assigned I have prototyped a patch that delays the array allocation of multiple arguments for `Enumerable#find`, `#any?` etc. https://github.com/ruby/ruby/pull/11110 ``` $ ./miniruby bench.rb ruby 3.4.0dev (2024-07-05T17:35:30Z lazy-alloc-of-bloc.. 264a1d8810) [x86_64-linux] Allocated 1 for dummy_hash.any? { |k, v| } Allocated 1 for dummy_hash.each { |k, v| } Allocated 5 for dummy_hash.find { |k, v| } Allocated 10000 for dummy_hash.any? { |k| } ``` `Enumerable#find`, `#all?`, etc. no longer allocate an Array as long as the predicate block returns falsy. However, there is a cost of calling `#each` method, so the performance would be slightly less than direct implementation like Hash#any?. This patch introduces a flag for ifunc. I'm not sure if this issue is worth the complexity. @ko1 What do you think? ---------------------------------------- Bug #20608: Hash#find always allocates each iterated pair https://bugs.ruby-lang.org/issues/20608#change-108965 * Author: ivoanjo (Ivo Anjo) * Status: Assigned * Assignee: ko1 (Koichi Sasada) * ruby -v: ruby 3.4.0preview1 (2024-05-16 master 9d69619623) [x86_64-linux] * Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN ---------------------------------------- Hey there! Recently I ran into this sharp edge in `Hash#find`: ```ruby puts RUBY_DESCRIPTION def allocated_now = GC.stat(:total_allocated_objects) dummy_hash = 10_000.times.each_with_index.to_h before_allocs = allocated_now dummy_hash.any? { |k, v| } puts "Allocated #{allocated_now - before_allocs} for #{File.read(__FILE__).lines[__LINE__-2]}" before_allocs = allocated_now dummy_hash.each { |k, v| } puts "Allocated #{allocated_now - before_allocs} for #{File.read(__FILE__).lines[__LINE__-2]}" before_allocs = allocated_now dummy_hash.find { |k, v| } puts "Allocated #{allocated_now - before_allocs} for #{File.read(__FILE__).lines[__LINE__-2]}" before_allocs = allocated_now dummy_hash.any? { |k| } puts "Allocated #{allocated_now - before_allocs} for #{File.read(__FILE__).lines[__LINE__-2]}" ``` Result: ``` ruby 3.4.0preview1 (2024-05-16 master 9d69619623) [x86_64-linux] Allocated 0 for dummy_hash.any? { |k, v| } Allocated 0 for dummy_hash.each { |k, v| } Allocated 10002 for dummy_hash.find { |k, v| } Allocated 10000 for dummy_hash.any? { |k| } ``` That is, while `Hash#any?`, `Hash#each`, etc avoid doing any allocations during iteration, `Hash#find` does not hit the `rb_block_pair_yield_optimizable` => `each_pair_i_fast` fast path, and so is massively costly compared to the others. This is very surprising, as I'd expect a `find` to have a comparable cost to `any?` (and I ended up [redoing some code to avoid find](https://github.com/DataDog/dd-trace-rb/pull/3757)). Also while experimenting a bit, it was surprising to me that the allocation optimization only kicks in when `|k, v|` are declared, and thus `.any? { |k| }` is also more expensive. -- https://bugs.ruby-lang.org/

Issue #20608 has been updated by ivoanjo (Ivo Anjo). Amazing, thank you! ---------------------------------------- Bug #20608: Hash#find always allocates each iterated pair https://bugs.ruby-lang.org/issues/20608#change-109048 * Author: ivoanjo (Ivo Anjo) * Status: Closed * Assignee: ko1 (Koichi Sasada) * ruby -v: ruby 3.4.0preview1 (2024-05-16 master 9d69619623) [x86_64-linux] * Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN ---------------------------------------- Hey there! Recently I ran into this sharp edge in `Hash#find`: ```ruby puts RUBY_DESCRIPTION def allocated_now = GC.stat(:total_allocated_objects) dummy_hash = 10_000.times.each_with_index.to_h before_allocs = allocated_now dummy_hash.any? { |k, v| } puts "Allocated #{allocated_now - before_allocs} for #{File.read(__FILE__).lines[__LINE__-2]}" before_allocs = allocated_now dummy_hash.each { |k, v| } puts "Allocated #{allocated_now - before_allocs} for #{File.read(__FILE__).lines[__LINE__-2]}" before_allocs = allocated_now dummy_hash.find { |k, v| } puts "Allocated #{allocated_now - before_allocs} for #{File.read(__FILE__).lines[__LINE__-2]}" before_allocs = allocated_now dummy_hash.any? { |k| } puts "Allocated #{allocated_now - before_allocs} for #{File.read(__FILE__).lines[__LINE__-2]}" ``` Result: ``` ruby 3.4.0preview1 (2024-05-16 master 9d69619623) [x86_64-linux] Allocated 0 for dummy_hash.any? { |k, v| } Allocated 0 for dummy_hash.each { |k, v| } Allocated 10002 for dummy_hash.find { |k, v| } Allocated 10000 for dummy_hash.any? { |k| } ``` That is, while `Hash#any?`, `Hash#each`, etc avoid doing any allocations during iteration, `Hash#find` does not hit the `rb_block_pair_yield_optimizable` => `each_pair_i_fast` fast path, and so is massively costly compared to the others. This is very surprising, as I'd expect a `find` to have a comparable cost to `any?` (and I ended up [redoing some code to avoid find](https://github.com/DataDog/dd-trace-rb/pull/3757)). Also while experimenting a bit, it was surprising to me that the allocation optimization only kicks in when `|k, v|` are declared, and thus `.any? { |k| }` is also more expensive. -- https://bugs.ruby-lang.org/