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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.

Class diagram

Half-Sync/Half-Async class diagram


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.

Real world examples