Avoid recalculating CounterCache.counter_cached_association_names

[fatkodima]

After merging #49866, a flaky test started to appear - https://buildkite.com/rails/rails/builds/101543#018b9610-f396-4e76-90e9-5bae14521f1e and https://buildkite.com/rails/rails/builds/101530#018b9485-eef8-49a9-8826-be82230fe7fe

from /rails/activesupport/lib/active_support/core_ext/module/redefine_method.rb:20:in `define_method'
from /rails/activesupport/lib/active_support/core_ext/module/redefine_method.rb:20:in `redefine_method'
from /rails/activesupport/lib/active_support/core_ext/module/redefine_method.rb:27:in `redefine_singleton_method'
from /rails/activerecord/lib/active_record/counter_cache.rb:10:in `counter_cached_association_names='
from /rails/activerecord/lib/active_record/counter_cache.rb:194:in `load_schema'
from /rails/activerecord/lib/active_record/model_schema.rb:423:in `columns_hash'
from /rails/activerecord/lib/active_record/locking/optimistic.rb:161:in `locking_enabled?'
from /rails/activerecord/lib/active_record/locking/optimistic.rb:60:in `locking_enabled?'
from /rails/activerecord/lib/active_record/locking/optimistic.rb:148:in `_query_constraints_hash'
from /rails/activerecord/lib/active_record/persistence.rb:944:in `update_columns'
from /rails/activerecord/lib/active_record/encryption/encryptable_record.rb:191:in `block in decrypt_attributes'
from /rails/activerecord/lib/active_record/encryption/contexts.rb:40:in `with_encryption_context'
from /rails/activerecord/lib/active_record/encryption/contexts.rb:50:in `without_encryption'
from /rails/activerecord/lib/active_record/encryption/encryptable_record.rb:191:in `decrypt_attributes'
from /rails/activerecord/lib/active_record/encryption/encryptable_record.rb:166:in `decrypt'
from /rails/activerecord/test/cases/encryption/concurrency_test.rb:22:in `block (2 levels) in thread_encrypting_and_decrypting'
from /rails/activerecord/test/cases/encryption/concurrency_test.rb:20:in `each'
from /rails/activerecord/test/cases/encryption/concurrency_test.rb:20:in `with_index'
from /rails/activerecord/test/cases/encryption/concurrency_test.rb:20:in `block in thread_encrypting_and_decrypting'

The failing line is the

rails/activerecord/test/cases/encryption/concurrency_test.rb

Line 22 in 8c82595

article.decrypt

which calls down the road

rails/activerecord/lib/active_record/locking/optimistic.rb

Lines 160 to 162 in 8c82595

	def locking_enabled?
	lock_optimistically && columns_hash[locking_column]
	end

which calls columns_hash which always calls load_schema which always recalculates and reassigns counter_cached_association_names https://github.com/rails/rails/pull/49866/files#diff-0441501ea93f2580c66bc58d845fcc2ad9dc5110cce249ce184c0b59483e253bR188-R194

Since the failing test from the referenced builds uses threads and counter_cached_association_names is defined as a class_attribute which is defined via

rails/activesupport/lib/active_support/core_ext/class/attribute.rb

Line 108 in 8c82595

redefine_singleton_method(:#{name}) { value }

which calls redefined_method and which is defined as

rails/activesupport/lib/active_support/core_ext/module/redefine_method.rb

Lines 17 to 22 in 8c82595

	def redefine_method(method, &block)
	visibility = method_visibility(method)
	silence_redefinition_of_method(method)
	define_method(method, &block)
	send(visibility, method)
	end

Lines 19-20 should be executed atomically, but I suspect, that Thread1 executes line 19, Thread2 executes line 19, then Thread1 executes line 20 and when Thread2 tries to execute line 20, it gets the mentioned error.

cc @byroot @nvasilevski

[byroot]

Good catch.