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-ThreadingIntroductory UsageProven PracticesOverture

3. Hello to the threading world

4. BlockingThread.Sleep & JoinLockinglock, Mutex & SemaphoreSinglingEventWaitHandle& Wait/PulseNon-BlockingMemory Barrier, Interlocked & VolatileManaging

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 lockAdvantage: Can work across processes, meaning multiple applications can use a single mutexMutex

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 notificationConsole.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 InterruptThrows – ThreadAbortExceptionDoes not wait for blockingAbort

13. Using non-blocking management

14. Using the built in ThreadPools

15. Single thread pool per processBuilt in logic to grow and shrink poolBuilt-in LimitsWorker threads – 25 per CPUI/O threads – 1000 per CPUThread Pools

16. Threaded controls in WinForms

17. TimersSource 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 ShanahanUnderstatement?

20. CostThread SafetyRace conditionsDead locksException ManagementDebuggingCommon Problems

21. 1 Mb of Address space12k for kernel mode stackNotification of every DLL in the processThreads are expensive

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

23. If file does not existCreate itPopulate it with initial dataRead data from fileProcess dataWrite to fileLogical Process I

24. If file does not existCreate itPopulate it with initial data (Write Lock)Read data from file (Read Lock)Process dataWrite to file (Write Lock – if needed)Release locksLogical Process II

25. Creates fileLocks writerAttempts to lock readerWaits…Locks ReaderProcesses dataAttempts to lock writerWaits…Thread 1Thread 2Dead Locks

26. Exceptions are limited to a threadExceptionsMainChildtry{}catch{}1

27. Debugging in Visual Studio

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

29. Be careful what you locklock’s are type based shared across all AppDomains. Use static as the solutionthis (instances) have a high chance of deadlocksUse lock over MonitorIf you must use Monitor, use try...finallyInside a lock do as little as possibleIf you are doing math inside the lock rather change to InterlockedNever perform long running operations on the UI threadProven Practises II