38 lines
1.6 KiB
Markdown
38 lines
1.6 KiB
Markdown
---
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layout: pattern
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title: Half-Sync/Half-Async
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folder: half-sync-half-async
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permalink: /patterns/half-sync-half-async/
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categories: Concurrency
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tags:
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- Performance
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---
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## Intent
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The Half-Sync/Half-Async pattern decouples synchronous I/O from
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asynchronous I/O in a system to simplify concurrent programming effort without
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degrading execution efficiency.
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## Class diagram
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## Applicability
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Use Half-Sync/Half-Async pattern when
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* a system possesses following characteristics:
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* the system must perform tasks in response to external events that occur asynchronously, like hardware interrupts in OS
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* it is inefficient to dedicate separate thread of control to perform synchronous I/O for each external source of event
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* the higher level tasks in the system can be simplified significantly if I/O is performed synchronously.
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* one or more tasks in a system must run in a single thread of control, while other tasks may benefit from multi-threading.
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## Real world examples
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* [BSD Unix networking subsystem](https://www.dre.vanderbilt.edu/~schmidt/PDF/PLoP-95.pdf)
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* [Real Time CORBA](http://www.omg.org/news/meetings/workshops/presentations/realtime2001/4-3_Pyarali_thread-pool.pdf)
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* [Android AsyncTask framework](http://developer.android.com/reference/android/os/AsyncTask.html)
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## Credits
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* [Douglas C. Schmidt and Charles D. Cranor - Half Sync/Half Async](https://www.dre.vanderbilt.edu/~schmidt/PDF/PLoP-95.pdf)
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* [Pattern Oriented Software Architecture Vol I-V](http://www.amazon.com/Pattern-Oriented-Software-Architecture-Volume-Patterns/dp/0471958697)
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