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.NET Fest 2018. Владимир Крамар. Многопоточное и асинхронное программирование в .NET
- 1. Multithreading & Async programming in .Net (Controversial topics and common mistakes) Vladimir Kramar
- 2. 1. What is a thread itself? 2. How to create a new thread? 3. Async - Why & Where? 4. Async & locking. 5. Exceptions in async methods. 6. Tricks & Hints. 7. Closing thoughts. Agenda
- 3. What is a thread itself?
- 4. How to create a new thread? • Thread • ThreadPool • System.Threading.Timer • APM - IAsyncResult, BeginInvoke(), EndInvoke() • EAP - BackgroundWorker • TAP - Task and Async / Await approach .Net 1.x .Net 2.0 .Net 4.x
- 5. System.Threading.Thread We should not use this class unless: We need to set a stack size, apartment state or culture for a new thread. We need immediately execute a new thread. We need a task running in foreground mode. We need a thread to have a particular priority. We have a task that might run a long time.
- 6. Why not ThreadPool? ThreadPool can be used something like this: • Messy! Is not it? • What if we have to wait for many threads to complete? • How do we capture the return values from multiple threads? • How do we return the control back to GUI threads?
- 7. System.Threading.Timer No – Thread.Sleep() Yes – To using of Timer
- 8. Asynchronous Patterns • APM Asynchronous Programming Model (IAsyncResult) • EAP Event-based Asynchronous Pattern (BackgroundWorker) • TAP Task-based Asynchronous Pattern (Task & async / await)
- 9. IAsyncResult (with callback) IAsyncResult – with callback Async / Await – with void method
- 10. IAsyncResult – without callback Async / Await – with Task async method IAsyncResult (without callback)
- 11. Why Async / Await is better? • Implementing of one method instead of two. • More readable implementation. • Copying the thread context. • Ability to track async operations progress. • Ability to create cold async operations.
- 12. How to create a new thread? • TAP - Task and Async / Await approach • Thread • ThreadPool • System.Threading.Timer • APM - IAsyncResult, BeginInvoke(), EndInvoke() • EAP - BackgroundWorker In most cases: In some special cases: Do not use it:
- 13. Async – Why & Where?
- 14. Async – Why & Where? Difference between Multithreading and Asynchronous programming: Multithreading: Async (better approach):
- 15. Async – Why & Where? Difference between Multithreading and Asynchronous programming: Better just to execute it with a new thread: General methods can not be executed as asynchronous even if we use async / await:
- 16. Async – Why & Where?
- 17. Async – Why & Where? Why? – To increase scalability. Where? – Whenever it is possible for long-running operations.
- 18. Under a hood of Async / Await. Let’s look at this async method: Behind the scene it performs the following: • Copying all local variable values. • Copying ‘this’ object state. • Tracking some other state data like a current stack pointer, await number, etc. • Remembering Synchronization and other thread contexts. • Then restoring all these data in callback threads. • And then the GarbageCollector should clean all taken memory.
- 19. Async & Locking
- 20. Locking with Async / Await We could use Mutex or Semaphore for locking like this:
- 21. Locking with Async / Await Only the SemaphoreSlim supports an async lock for now:
- 22. Exceptions in async methods
- 23. Exceptions in async void We should not implement async void methods due to we never can catch their exceptions.
- 24. Handling exceptions in async And then we can log this way:Just one extension method:
- 25. Tricks & Hints
- 27. Discarding the contexts We can prevent copying of thread context data: In async / await methods: For new threads:
- 28. Thread stack size IIS: In Windows Server 2008 and higher, the maximum stack size of a thread running on 32- bit version of IIS is 256 KB, and on an x64 server is 512 KB. Before, the max stack size of a thread in IIS equalled to 1 MB. Diminishing of a stack size can increase scalability and consequently performance of an application. For changing a stack size in Windows OS we can use editbin cmd utility like this:
- 29. Viewing a stack size The fragment of an output: To get information about stack size of your app, you can use dumpbin cmd utility: dumpbin /headers MyApp.exe > info.txt The 400000 is size in heximal value. So in decimal it equals to 4194304 bytes or 4 Mb
- 30. Closing Thoughts