What is "directplay"

DirectPlay is a deprecated API that was part of Microsoft's DirectX API. DirectPlay is a network communication library intended for computer game development, although its general nature certainly allows it to be used for other purposes.

DirectPlay is a high-level software interface between applications and communication services that makes it easy to connect games over the Internet, a modem link, or a network. DirectPlay features a set of tools that allow players to find game sessions and sites to manage the flow of information between hosts and players. It provides a way for applications to communicate with each other, regardless of the underlying online service or protocol. DirectPlay also resolves many connectivity issues, such as NAT.

DirectPlay, like the rest of DirectX, runs in COM and it is accessed through COM (Component Object Model) interfaces. By default, DirectPlay uses multi-threaded programming techniques and requires careful thought to avoid the usual threading issues. Since DirectX version 9, this issue can be alleviated at the expense of efficiency.