Half-sync/half-async: an architectural pattern for efficient and well-structured concurrent I/O
Douglas C. Schmidt, Charles D. Cranor · 1996
This paper describes the Half-Sync/Half-Async pattern, which integrates synchronous and asynchronous I/O models to support both programming simplicity and execution efficiency in complex concurrent software systems. In this pattern, higher-level tasks use a synchronous I/O model, which simplifies concurrent programming. In contrast, lower-level tasks use an asynchronous I/O model, which enhances execution efficiency. This pattern is widely used in operating systems such as UNIX, Mach, WindowsNT, and VMS, as well as other complex concurrent systems. 1 Intent The Half-Sync/Half-Async pattern decouples synchronous I/O from asynchronous I/O in a system to simplify concurrent programming effort without degrading execution efficiency. 2 Motivation To illustrate the Half-Sync/Half-Async pattern, consider the software architecture of the BSD UNIX [1] networking subsystem shown in Figure 1. The BSD UNIX kernel coordinates I/O between asynchronous communication devices (such as network adapter...