如今的Web应用、 Silverlight以及各种分布式系统让异步解决方案有了更进一步的需求。F#是微软.NET平台上的函数式编程语言，并添加了不少让并行及异步编程变得有趣且轻松的特性。本次演讲将讨论F#的核心概念，并探讨F#中的不可变性、函数式设计、异步工作流、代理等特性是如何应对真实应用中的异步挑战的。

1. Async Programming in
F#
Zhao Jie - SNDA - June 2010

2. About Me
• / / Jeffrey Zhao /
• Programmer
• Blogger - http://blog.zhaojie.me/
• Twitterer: @jeffz_cn
• F#, Scala, JavaScript, Python, .NET, mono...
• Java (as the language) hater

3. What’s F#
• Languages by Don Syme, MS Research
• Strongly Statically Typed Language
• Functional Language with OO Ability
• General Purpose Language

4. Async programming is
complex ...

5. ...and will only get
more complex in the
near future

6. Four Big Concurrency
Challenges
• Shared State
• Code Locality
• I/O Parallelism
• Scaling Up

7. Shared State
• Difficult to maintain and test
• Very difficult to parallelize
• Locking is fundamentally error prone
‣ Must guess where parallelism is needed
‣ All consumers need to participate

8. Demo: Immutability

9. Immutability in F#
• Immutable Union • Immutable Tuple
• Immutable Record • Immutable List
• Immutable Set • Immutable Map
• Immutable Objects • Immutable ...

10. Code Locality
• Used to expressing algorithms linearly
• Async requires logical division of algorithms
• Very difficult to
‣ Combine multiple asynchronous operations
‣ Deal with exceptions and cancellation

11. Asynchronous Workflow
async
{
...
}

12. React
async
{
let!
res
=
<async
work>
...
}
an HTTP Response
an UI Event
a Timer Callback
a Query Response
a Web Servcie Response
a Disk I/O Completion
an Agent Message

13. async
{
let!
img
=
AsyncRead
"http://..."
printfn
"loaded!"
do!
AsyncWrite
img
@"c:..."
printfn
"saved!"
}
=
async.Delay(fun
-­‐>
async.Bind(AsyncRead
"http://...",
(fun
img
-­‐>
printfn
"loaded!"
async.Bind(AsyncWrite
img
@"c:...",
(fun
()
-­‐>
printfn
"saved!"
async.Return())))))

14. Demo: Code Locality

15. I/O Parallelism
• Software is often I/O-bound
‣ Leveraging web services
‣ Working with data on disk
• Network and disk speeds increasing slower
• I/O resources are inherently parallel
‣ Huge opportunity for performance

16. Demo: I/O Parallelism

17. Scaling to Multi-Machine
• To scale up, must to go beyond a single machine
• Multi-machine resources becoming common
‣ Roll-you-own clusters with cheap hardware
‣ On-demand cloud compute with Azure
• But
‣ Shared memory doesn’t scale

18. ... the principle we go by is, don't expect to see
a particular concurrency model put into C#
because there're many different concurrency
model ... it's more about finding things are
common to to all kinds of concurrency ...
- Anders Hejlsberg

19. Demo: Agents

20. Concurrency Challenges
• Shared State - Immutability
• Code Locality - async { ... }
• I/O Parallelism - async { ... }
• Scaling to Multi-Machine - Agents

21. F#
• Modern, simple, powerful and productive
• Ready for production use with VS 2010
• Simplified parallel and async programming
for today and tomorrow
• Support .NET 4.0 / 3.5 and mono
• Open Source *

22. F# Resources
http://fsharp.net
Programming F# Expert F# 2.0 Real World FP

23. Q &A

24. Thanks!