A Solution: Asynchronous I/O

To overcome the issue of blocking calls discussed in the last lesson, many modern operating systems have introduced new ways to issue I/O requests to the disk system, referred to generically as asynchronous I/O. These interfaces enable an application to issue an I/O request and return control immediately to the caller before the I/O has completed; additional interfaces enable an application to determine whether various I/Os have completed.

An example: Mac’s API

For example, let us examine the interface provided on a Mac (other systems have similar APIs). The APIs revolve around a basic structure, the struct aiocb, or AIO control block in common terminology. A simplified version of the structure looks like this (see the manual pages for more information):