If a reload is in progress from another thread when ShardRegistry::reload() is called, the later ShardRegistry::reload() joins the current one.

Once the current reload completes, the later call returns false to indicate that it did not perform its own reload.

This leads to using the pattern:

if (!Grid::get(txn)->shardRegistry()->reload(txn)) {
    // If the first reload joined an existing one, call reload again to ensure the reload is fresh.
    Grid::get(txn)->shardRegistry()->reload(txn);
}

This pattern should be encompassed in a forceReload() method on the ShardRegistry.