1. 1. Summary

Fixes WiredTiger timestamp conflicts in Antithesis testing when multiple ValidateCollections hooks run concurrently on the same MongoDB cluster.

1. 1. Problem

In FSM workload tests with `maxTestQueueSize > 1`, concurrent test jobs share the same MongoDB fixture. When tests complete, their ValidateCollections hooks run simultaneously, causing conflicts:

• Job 1's hook inserts into `test.validate.hook` at timestamp T for internode validation
• Job 2's hook runs validate commands concurrently, reading at timestamp T
• *Conflict*: Job 1 cannot commit at T because Job 2 is already reading at T
• *Error*: `commit timestamp must be after all active read timestamps`

1. 1. Solution

Add a global `threading.Lock` to serialize ValidateCollections hooks across all jobs:

• *replicaset.py*: Define `_GLOBAL_VALIDATION_LOCK` at module level
• *shardedcluster.py*: Reference the same lock via `_validation_lock` attribute
• *validate.py*: Acquire fixture's `_validation_lock` before running validation

Only one ValidateCollections hook can execute at a time, preventing timestamp conflicts while maintaining backward compatibility with fixtures that lack the lock.

1. 1. Why SERVER-115225 Wasn't Enough

SERVER-115225 improved timestamp accuracy for a single hook but didn't address concurrent hooks running on the same cluster.