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get_named_validator returns one validator shared across threads; concurrent validation fails with _RefResolutionError #1434
Description
Summary
adcp.validation.schema_loader.get_named_validator caches one Draft7Validator per schema, built on jsonschema's legacy RefResolver, and returns that same instance to every caller. RefResolver keeps a mutable scope stack: following a $ref into another document pushes that document's scope, and leaving pops it. When two threads validate with the shared validator at the same time, one thread can resolve #/definitions/... against the other thread's document and fail with _RefResolutionError: Unresolvable JSON pointer.
Versions: adcp 8.0.0, jsonschema 4.25.1, Python 3.13.
Reproduction
import collections, threading
from adcp.validation.schema_loader import get_named_validator
validator = get_named_validator("core/targeting-overlay-support.json", version="3.2")
declaration = {
"geo_countries": True,
"geo_metros": {"systems": ["nielsen_dma"]},
"geo_postal_areas": {"US": ["zip"]},
"frequency_cap": True,
}
errors = collections.Counter()
def work():
for _ in range(300):
try:
list(validator.iter_errors(declaration))
except Exception as exc:
errors[f"{type(exc).__name__}: {exc}"] += 1
threads = [threading.Thread(target=work) for _ in range(8)]
for t in threads: t.start()
for t in threads: t.join()
print(dict(errors))Output:
{"_RefResolutionError: Unresolvable JSON pointer: 'definitions/countrySupport'": 1259,
"_RefResolutionError: Unresolvable JSON pointer: 'definitions/supported'": 6}
Run on a single thread, the same declaration validates with no errors.
Impact
Any threaded server that validates with get_named_validator (Flask, or WSGI under a threaded worker) fails intermittently under concurrent requests. We hit it in production-like traffic on a management API that validates overlay_support declarations.
The task validators in schema_loader are built and cached the same way (state.compiled plus RefResolver). We haven't reproduced it there, but they may share the problem.
Suggested fix
Any of these would work:
- Build the validator on
referencing.Registry(jsonschema ≥ 4.18), which keeps no per-validation mutable state. - Cache only the schema and store, and return a validator with a fresh
RefResolverper call. - Cache validators per thread.
Workaround
We build a validator per call, with its own resolver over the cached validator's schema, base URI and store (the store is only read):
shared = get_named_validator(path, version=version)
resolver = RefResolver(base_uri=shared.resolver.base_uri, referrer=shared.schema, store=shared.resolver.store)
validator = Draft7Validator(shared.schema, resolver=resolver, format_checker=shared.format_checker)
Activity
bokelley commentedon Oct 7, 2026
Triage
Classification: Bug
Bucket(s): validation (no
validationlabel in repo — gap noted for maintainers)Status: ready-to-implement
What the experts said:
get_named_validator(L765) andget_validator(L693) cache aDraft7Validatorholding a shared mutableRefResolver._scopes_stack; concurrentiter_errors()corrupts the scope stack — blocker, fix both in one patch.--threads, uWSGIenable-threads); freshRefResolverper call is unconditionally correct since the scope stack is local to one traversal and the store is read-only; non-breaking semver patch.My take: This is a hard crash under any concurrent validation workload, not an edge case. Both functions must be fixed together — patching only
get_named_validatorleaves the higher-trafficget_validatorpath (called on everyvalidate_request/validate_response) broken.Implementation scope:
src/adcp/validation/schema_loader.pyonly. Add a_ValidatorSpec(schema, base_uri, store, format_checker)dataclass; cache it instate.compiled/state.named_compiledinstead of the validator. Have bothget_*functions callspec.make()—_make_ref_resolver(…)+Draft7Validator(…)— on each return. Schema I/O and_reachable_schema_storegraph walk stay cached; only the O(1) RefResolver + validator construction moves to call time. Preservereferrer=schema(not{}) in every freshRefResolver— load-bearing for fragment-only$defsrefs.core/targeting-overlay-support.json) confirming zero_RefResolutionErrorexceptions.pytest tests/·mypy src/·ruff check .·black --check .Draft7Validatorbehavior is identical; object identity across calls was never documented.Triaged by Claude Code. Session: https://claude.ai/code/session_015eyJqam8c1ZMC8TvovbLu4
Generated by Claude Code