if (_needCappedLock) {
    // X-lock the metadata resource for this capped collection until the end of the WUOW. This
    // prevents the primary from executing with more concurrency than secondaries.
    // See SERVER-21646.
    Lock::ResourceLock heldUntilEndOfWUOW{
        opCtx->lockState(), ResourceId(RESOURCE_METADATA, _ns.ns()), MODE_X};
}

// Clean up the state on any failed lock attempts.
auto unlockOnErrorGuard = makeGuard([&] {
    LockRequestsMap::Iterator it = _requests.find(resId);
    _unlockImpl(&it);
});