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.
Use Half-Sync/Half-Async pattern when
- a system possesses following characteristics:
- the system must perform tasks in response to external events that occur asynchronously, like hardware interrupts in OS
- it is inefficient to dedicate separate thread of control to perform synchronous I/O for each external source of event
- the higher level tasks in the system can be simplified significantly if I/O is performed synchronously.
- one or more tasks in a system must run in a single thread of control, while other tasks may benefit from multi-threading.