Maciej Mensfeld created AVRO-4256:
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Summary: Ruby gem incompatible with Ruby 4.0 Ractors:
non-shareable constants, closures, and mutable class-level state
Key: AVRO-4256
URL: https://issues.apache.org/jira/browse/AVRO-4256
Project: Apache Avro
Issue Type: Bug
Components: ruby
Affects Versions: 1.12.1
Environment: Ruby 4.0.3 (2026-04-21), Linux x86_64, avro gem 1.12.1
Reporter: Maciej Mensfeld
Attachments: avro_ractor_poc.rb
```
h3. Description
The {{avro}} Ruby gem (1.12.x) cannot be used inside
[Ractors|https://docs.ruby-lang.org/en/master/Ractor.html] on Ruby 4.0. Every
common operation - parsing schemas, serializing records, even reading constants
- fails with {{Ractor::IsolationError}} or {{{}RuntimeError{}}}.
This blocks any use of Ractors for parallel Avro serialization/deserialization.
h3. Root causes
*1. Non-shareable Set constants ({{{}lib/avro/schema.rb:24-31{}}})*
{{{}PRIMITIVE_TYPES{}}}, {{{}NAMED_TYPES{}}}, {{VALID_TYPES}} and their
{{_SYM}} variants are plain {{Set}} objects - not frozen, not Ractor-shareable.
*2. Un-shareable Proc/closure in method definitions
({{{}lib/avro/schema.rb:239{}}})*
{{Schema#to_s}} and other methods are defined with closures that capture
non-shareable state.
*3. Mutable module-level instance variables ({{{}lib/avro.rb:38-55{}}})*
{{{}@disable_enum_symbol_validation{}}},
{{{}@disable_field_default_validation{}}}, {{@disable_schema_name_validation}}
are mutable class-level state that non-main Ractors cannot access.
h3. Test output
{code:java}
Ruby version: 4.0.3
Avro version: 1.12.1
## 1. Access Avro::Schema::PRIMITIVE_TYPES constant in a Ractor
FAILED: Ractor::IsolationError: can not access non-shareable objects in
constant Avro::Schema::PRIMITIVE_TYPES by non-main Ractor.
## 2. Access Avro::Schema::VALID_TYPES constant in a Ractor
FAILED: Ractor::IsolationError: can not access non-shareable objects in
constant Avro::Schema::VALID_TYPES by non-main Ractor.
## 3. Parse an Avro schema inside a Ractor
FAILED: RuntimeError: defined with an un-shareable Proc in a different Ractor
## 4. Pass a pre-parsed Schema object into a Ractor
FAILED: RuntimeError: defined with an un-shareable Proc in a different Ractor
## 5. Encode a record using DatumWriter inside a Ractor
FAILED: Ractor::IsolationError: can not access non-shareable objects in
constant Avro::Schema::VALID_TYPES_SYM by non-main Ractor.
## 6. Read Avro.disable_enum_symbol_validation inside a Ractor
FAILED: Ractor::IsolationError: can not set instance variables of
classes/modules by non-main Ractors
{code}
h3. Suggested fixes
# Freeze all {{{}Set{}}}/{{{}Hash{}}}/{{{}Array{}}} constants with
{{Ractor.make_shareable}} or {{.freeze}}
# Replace closures with regular {{def}} method definitions instead of
{{define_method}} with blocks
# Replace mutable module-level {{@ivars}} with Ractor-local storage or frozen
configuration
h3. Reproduction script
Self-contained script using bundler/inline - save as {{avro_ractor_poc.rb}} and
run with {{{}ruby avro_ractor_poc.rb{}}}.
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