On Dynamic Plug-in Loading with Ada 95 and Ada 2005

摘要

Maintenance of high-availability systems (e.g., servers) requires the ability to modify, enhance, or correct parts of the application without having to stop and re-link the entire system. This capability is relatively straight-forward with interpreted languages or virtual-machine based languages such as Java, in which new code is loaded upon demand. In languages typically implemented with static executable images this capability can be offered though dynamically loaded/linked libraries ("DLLs"). However, in practice it is impractical to make full use of this capability because the protocol for invoking subprograms in a DLL is very low-level and unsafe. In the case of Ada, global coherency requirements and elaboration ordering constraints add an additional degree of complexity over less strict/safe languages.