Bug: thread safety issues during validation

[pgarrett-twc]

Is there an existing issue for this?

• I have searched the existing issues

Current Behavior

When I run schema.validate(doc) {} from multiple threads simultaneously, I frequently get one of these errors:

java.util.NoSuchElementException: ArrayDeque is empty.
	at kotlin.collections.ArrayDeque.removeLast(ArrayDeque.kt:165)
	at io.github.optimumcode.json.schema.internal.DefaultReferenceResolver.popSchemaPath(ReferenceResolver.kt:65)
	...

or

java.lang.ArrayIndexOutOfBoundsException: arraycopy: last source index 549 out of bounds for object array[366]
	at java.base/java.lang.System.arraycopy(Native Method)
	at kotlin.collections.ArraysKt___ArraysJvmKt.copyInto(_ArraysJvm.kt:932)
	at kotlin.collections.ArrayDeque.copyElements(ArrayDeque.kt:74)
	at kotlin.collections.ArrayDeque.ensureCapacity(ArrayDeque.kt:66)
	at kotlin.collections.ArrayDeque.addLast(ArrayDeque.kt:136)
	at io.github.optimumcode.json.schema.internal.DefaultReferenceResolver.pushSchemaPath(ReferenceResolver.kt:61)
	...

When I run the same code either single-threaded, or with a ThreadLocal copy of the JsonSchema, there are no errors.

Expected Behavior

It would be nice if the schema could be used safely from multiple simultaneous threads.

However, I don't think the documentation states whether the library is expected to be thread-safe, so maybe it is not intended to be? I'm just reporting this in case it is not expected, since this being resolved in the library would simplify my code a bit.

JSON schema

Schema(s) supplied via recreation repo. https://github.com/pgarrett-twc/jsonschema-threadsafety/tree/main/src/test/resources

Library version

0.3.0

Anything else?

I've pushed a sample repo with a test that usually reproduces the problem:
https://github.com/pgarrett-twc/jsonschema-threadsafety/blob/main/src/test/kotlin/ThreadSafetyTests.kt#L40-L53

I've reproduced this with both Java 17 and 21, on ARM MacOS.

These are the full stack traces of the errors I've seen.
stack1.txt
stack2.txt

[OptimumCode]

Hi, @pgarrett-twc. Thank you for reporting this issue.

The problem is very simple - the reference resolver that is shared between validations has a mutable state. And because of that you are getting the errors you see.

I will take a look at how to avoid sharing the mutable state between invocations.

[OptimumCode]

Hi, @pgarrett-twc. The fix is available in the latest snapshot version 0.3.1-SNAPSHOT.

Once the release is published I will add a comment to this issue.

[pgarrett-twc]

Wow, thanks for the quick turnaround!

[OptimumCode]

Available in release 0.3.1