This document discusses .NET multi-threading concepts including blocking, locking, signaling, and non-blocking techniques. It provides code examples for managing threads using techniques like Join, lock, Mutex, and EventWaitHandle. It also covers thread pools, common problems like race conditions and deadlocks, and proven practices for safe multi-threaded programming.

1. Multi-Threading

2. .NET Multi-Threading Introductory Usage Proven Practices Overture

3. Hello to the threading world

4. Blocking Thread.Sleep & Join Locking lock, Mutex & Semaphore Singling EventWaitHandle& Wait/Pulse Non-Blocking Memory Barrier, Interlocked & Volatile Managing

5. Managing threads

6. static void Main() { Threadt = newThread (delegate() { Console.ReadLine(); }); t.Start(); t.Join(); // Wait until thread finishes /* Do next step */ } Join

7. lock(locker) { gate.Add(primeCounter); } Monitor.Enter(locker); try { gate.Add(primeCounter); } finally { Monitor.Exit(locker); } Sugary lock

8. Same as a lock Advantage: Can work across processes, meaning multiple applications can use a single mutex Mutex

9. staticEventWaitHandle wh = new AutoResetEvent(false); static void Main() { newThread (Waiter).Start(); Thread.Sleep (1000); // Wait for some time... wh.Set(); // OK - wake it up } static void Waiter() { Console.WriteLine("Waiting..."); wh.WaitOne(); // Wait for notification Console.WriteLine("Notified"); } Signalling

10. lock(locker) { gate.Add(primeCounter); } Thread.MemoryBarrier(); try { gate.Add(primeCounter); } finally { Thread.MemoryBarrier(); } Memory Barrier

11. static void Main() { Thread t = new Thread(delegate() { try { Thread.Sleep(Timeout.Infinite); // This is blocking } catch (ThreadInterruptedException) { Console.Write("Forcibly "); } Console.WriteLine("Woken!"); }); t.Start(); t.Interrupt(); } Interrupt

12. Similar usage to Interrupt Throws – ThreadAbortException Does not wait for blocking Abort

13. Using non-blocking management

14. Using the built in ThreadPools

15. Single thread pool per process Built in logic to grow and shrink pool Built-in Limits Worker threads – 25 per CPU I/O threads – 1000 per CPU Thread Pools

16. Threaded controls in WinForms

17. Timers Source Alex Calvo - http://msdn.microsoft.com/en-us/magazine/cc164015(printer).aspx

18. Talking to the UI thread from a worker thread

19. “Multi-threaded programming needs a little care” Patricia Shanahan Understatement?

20. Cost Thread Safety Race conditions Dead locks Exception Management Debugging Common Problems

21. 1 Mb of Address space 12k for kernel mode stack Notification of every DLL in the process Threads are expensive

22. Reads value (5) Adds 1 – (6) Assumes value 6 Reads value (6) Adds 1 – (7) Assumes value 7 Thread 1 Thread 2 Race Conditions

23. If file does not exist Create it Populate it with initial data Read data from file Process data Write to file Logical Process I

24. If file does not exist Create it Populate it with initial data (Write Lock) Read data from file (Read Lock) Process data Write to file (Write Lock – if needed) Release locks Logical Process II

25. Creates file Locks writer Attempts to lock reader Waits… Locks Reader Processes data Attempts to lock writer Waits… Thread 1 Thread 2 Dead Locks

26. Exceptions are limited to a thread Exceptions Main Child try { } catch { } 1

27. Debugging in Visual Studio

28. Threads are expensive – use wisely Use managed threads over native threads. Use Timers or ThreadPool where possible. Or the new parallel extensions in .NET 4.0 Avoid mutex, unless you need cross process. Avoid Thread.Abortas it can have high side effects Avoid Thread.Suspend/Resume as a blocking system Rather use lock Proven Practises I

29. Be careful what you lock lock’s are type based shared across all AppDomains. Use static as the solution this (instances) have a high chance of deadlocks Use lock over Monitor If you must use Monitor, use try...finally Inside a lock do as little as possible If you are doing math inside the lock rather change to Interlocked Never perform long running operations on the UI thread Proven Practises II

31. http://www.slideshare.net/rchakra/intro-to-net-threads http://www.slideshare.net/psteinb/threading-game-engines-quake-4-enemy-territory-quake-wars http://blog.zwares.com/2007/02/net-threads-10-best-practices.html http://www.yoda.arachsys.com/csharp/threads/ http://msdn.microsoft.com/en-us/library/hyz69czz.aspx http://msdn.microsoft.com/en-za/magazine/cc300429(en-us).aspx http://msdn.microsoft.com/en-us/library/3e8s7xdd(VS.71).aspx http://www.albahari.com/threading/ http://msdn.microsoft.com/en-us/library/ms951089.aspx http://www.gotw.ca/publications/concurrency-ddj.htm http://brahma.ananthonline.net/ http://research.microsoft.com/en-us/projects/Accelerator/ http://stackoverflow.com/questions/1355398/monitor-vs-waithandle-based-thread-sync http://www.bluebytesoftware.com/blog/PermaLink,guid,f8404ab3-e3e6-4933-a5bc-b69348deedba.aspx http://blogs.msdn.com/brada/archive/2004/05/12/130935.aspx http://msdn.microsoft.com/en-us/library/aa645755(VS.71).aspx http://msdn.microsoft.com/en-us/magazine/cc164015.aspx http://msdn.microsoft.com/en-us/library/ms951089(printer).aspx References