Concurrency - responsiveness in .NET
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The document discusses concurrency and asynchronous programming in .NET. It covers three pillars of concurrency: scalability using Parallel.For, responsiveness using tasks and async/await, and consistency using locks, mutexes, etc. It demonstrates how async/await allows programs to be responsive by freeing threads for other work while waiting for I/O. A key point is that the SynchronizationContext impacts asynchronous code behavior and can cause unintended threading issues if not properly understood.
Concurrency - responsiveness in .NET
- 2. Mårten Rånge Ericsson AB @marten_range
- 3. Concurrency Examples for .NET
- 5. Responsive
- 7. Three pillars of Concurrency Scalability (CPU) Parallel.For Responsiveness Task async/await Consistency lock Interlocked.* Mutex/Event/Semaphore Monitor
- 10. string ReadSomeText (string fileName) { using (var sr = new StreamReader(fileName)) { var result = sr.ReadToEnd (); return result; } } // Blocks the thread until IO completes var text = ReadSomeText ("SomeText.txt");
- 11. Asyncronous programming allows programs to be responsive
- 12. async Task<string> ReadSomeTextAsync(string fileName) { using (var sr = new StreamReader(fileName)) { var result = await sr.ReadToEndAsync(); return result; } }
- 13. async Task<string> ReadSomeTextAsync(string fileName) { using (var sr = new StreamReader(fileName)) { var result = await sr.ReadToEndAsync(); return result; } }
- 14. async Task<string> ReadSomeTextAsync(string fileName) { using (var sr = new StreamReader(fileName)) { var result = await sr.ReadToEndAsync(); return result; } }
- 15. async Task<string> ReadSomeTextAsync(string fileName) { using (var sr = new StreamReader(fileName)) { var first = await sr.ReadLineAsync(); var second = await sr.ReadLineAsync(); var third = await sr.ReadLineAsync(); return first + second + third; } }
- 16. async Task<string> ReadSomeTextAsync(string fileName) { using (var sr = new StreamReader(fileName)) { var result = await sr.ReadToEndAsync(); return result; } } // Is this code correct? var readTask = ReadSomeTextAsync ("SomeText.txt"); var text = readTask.Result;
- 17. It depends
- 18. // Is this code correct (ignore exceptions)? async Task<string> ReadSomeTextAsync(string fileName) { ++m_readingFiles; using (var sr = new StreamReader(fileName)) { var result = await sr.ReadToEndAsync(); --m_readingFiles; return result; } }
- 19. It depends
- 20. // Does both TraceTheadId() trace the same id? async Task<string> ReadSomeTextAsync(string fileName) { TraceThreadId (); using (var sr = new StreamReader(fileName)) { var result = await sr.ReadToEndAsync(); TraceThreadId (); return result; } }
- 21. It depends
- 22. What’s going on?
- 23. Your new ”best” friends SynchronizationContext Console apps Continues on ThreadPool thread WindowsFormsSynchronizationContext Used by WindowsForms apps Continues on the ”UI” thread DispatcherSynchronizationContext Used by WPF and ASP.NET apps Continues on the ”same” thread
- 25. async Task<string> ReadSomeTextAsync(string fileName) { using (var sr = new StreamReader(fileName)) { var result = await sr.ReadToEndAsync(); return result; } } // Is this code correct? var readTask = ReadSomeTextAsync ("SomeText.txt"); var text = readTask.Result;
- 26. Yes
- 27. // Is this code correct (ignore exceptions)? async Task<string> ReadSomeTextAsync(string fileName) { ++m_readingFiles; using (var sr = new StreamReader(fileName)) { var result = await sr.ReadToEndAsync(); --m_readingFiles; return result; } }
- 28. No
- 29. // Does both TraceTheadId() trace the same id? async Task<string> ReadSomeTextAsync(string fileName) { TraceThreadId (); using (var sr = new StreamReader(fileName)) { var result = await sr.ReadToEndAsync(); TraceThreadId (); return result; } }
- 30. No
- 32. async Task<string> ReadSomeTextAsync(string fileName) { using (var sr = new StreamReader(fileName)) { var result = await sr.ReadToEndAsync(); return result; } } // Is this code correct? var readTask = ReadSomeTextAsync ("SomeText.txt"); var text = readTask.Result;
- 33. No
- 34. // Is this code correct (ignore exceptions)? async Task<string> ReadSomeTextAsync(string fileName) { ++m_readingFiles; using (var sr = new StreamReader(fileName)) { var result = await sr.ReadToEndAsync(); --m_readingFiles; return result; } }
- 35. Yes
- 36. // Does both TraceTheadId() trace the same id? async Task<string> ReadSomeTextAsync(string fileName) { TraceThreadId (); using (var sr = new StreamReader(fileName)) { var result = await sr.ReadToEndAsync(); TraceThreadId (); return result; } }
- 37. Yes
- 38. So…
- 39. SynchronizationContext Is ”invisible” Is a thread-global state Impacts the behavior of your code significantly As an application developer you can make assumptions As a library developer you can’t make assumptions
- 40. ConfigureAwait
- 41. async Task<string> ReadSomeTextAsync(string fileName) { using (var sr = new StreamReader(fileName)) { var result = await sr.ReadToEndAsync() .ConfigureAwait (false); return result; } } // Is this code correct? var readTask = ReadSomeTextAsync ("SomeText.txt"); var text = readTask.Result;
- 42. Yes
- 43. // Is this code correct (ignore exceptions)? async Task<string> ReadSomeTextAsync(string fileName) { ++m_readingFiles; using (var sr = new StreamReader(fileName)) { var result = await sr.ReadToEndAsync() .ConfigureAwait (false); --m_readingFiles; return result; } }
- 44. No
- 45. // Does both TraceTheadId() trace the same id? async Task<string> ReadSomeTextAsync(string fileName) { TraceThreadId (); using (var sr = new StreamReader(fileName)) { var result = await sr.ReadToEndAsync() .ConfigureAwait (false); TraceThreadId (); return result; } }
- 46. No
- 47. async/await tries to be what we want
- 48. async/await reminds me of…
- 49. What we need Do one thing Responsiveness Predictable semantics Continuation is executed by a thread-pool thread Visibility Thread-switching should be visible in code
- 50. F# async // Focuses on responsiveness let gameLoop = async { // Switching to new thread is explicit do! Async.SwitchToNewThread () while true do // let! is like await in C# let! messages = fromVisual.AsyncDequeue 1000 for message in messages do processMessage message }
- 51. C# yield Special support for enumerators LINQ Special support for SQL-like syntax async/await Special support for asynchronous programming
- 52. F# seq { for x in 0..10 -> i } Enumerators implemented using Computation Expressions query { for c in db.Customers do select c } SQL-like syntax implemented using Computation Expressions async { let! r=fromVisual.AsyncDequeue 1000 in r } Asynchronous programming using Computation Expressions
- 54. With async/await always consider the…
- 55. SynchronizationContext SynchronizationContext SynchronizationContext SynchronizationContext SynchronizationContext SynchronizationContext SynchronizationContext SynchronizationContext SynchronizationContext SynchronizationContext SynchronizationContext
- 56. Mårten Rånge Ericsson AB @marten_range
- 57. Links Presentation http://www.slideshare.net/martenrange/ Code https://github.com/mrange/presentations/ DIY asynchronous workflows in F# http://mrange.wordpress.com/2014/06/12/diy-asynchronous-workflows- in-f/ Asynchronous programming with async/await http://msdn.microsoft.com/en-us/library/hh191443.aspx