它发生在 AssetsLibraryServices 中，就像线程不安全一样。像这样调用堆栈
libobjc.A.dylib
_objc_retain (in libobjc.A.dylib)
AssetsLibraryServices _pl_dispatch_once (in AssetsLibraryServices)
PhotoLibraryServices +[PLManagedAsset predicateToExcludeHiddenAssetsWithHiddenKeyPath:] (in PhotoLibraryServices)
Photos -[PHQuery _globalPredicatesForPHClass:] (in Photos)
Photos -[PHQuery effectivePredicateForPHClass:request:includingBasePredicate:] (in Photos)
Photos -[PHQuery _createFetchRequestIncludingBasePredicate:] (in Photos)
Photos -[PHQuery fetchRequest] (in Photos)
Photos -[PHFetchResult initWithQuery:oids:registerIfNeeded:usingManagedObjectContext:] (in Photos)
Photos -[PHFetchResult initWithQuery:] (in Photos)
Photos ___23-[PHQuery executeQuery]_block_invoke (in Photos)
Photos -[PHQuery executeQuery] (in Photos)
Photos +[PHAsset fetchAssetsInAssetCollection:options:] (in Photos)