This function returns an int, despite the fact that the design pattern for a size() method is consistently std::size_t.

This method and others should be homogenized to return std::size_t since a signed value is inappropriate and generates (1) sign-conversion warnings when compiled with strict flags, and (2) an [ERRFMT] in Poco::format when you naively assume it's a %z format (as most ::size() return values would be).

Ditto for: Poco::TimedNotificationQueue, Poco::NotificationQueue, Poco::PriorityNotificationQueue, Poco::Manifest, Poco::Crypto/RSAKey, Poco::Crypto::RSAKeyImpl...