Threading in C# Joseph Albahari Last updated 2011-4-27 Interested in a book on C# and .NET by the same author? See www.albahari.com/nutshell/ Table of Contents Part 1: Getting Started ..................................................................... 4 Introduction and Concepts .............................................................................. 4 Join and Sleep ....................................................................................... 6 How Threading Works ......................................................................... 7 Threads vs Processes ............................................................................ 7 Threading’s Uses and Misuses ............................................................. 8 Creating and Starting Threads ........................................................................ 8 Passing Data to a Thread ...................................................................... 9 Naming Threads ................................................................................. 11 Foreground and Background Threads ................................................ 11 Thread Priority.................................................................................... 12 Exception Handling ............................................................................ 12 Thread Pooling .............................................................................................. 14 Entering the Thread Pool via TPL ...................................................... 15 Entering the Thread Pool Without TPL .............................................. 16 Optimizing the Thread Pool ............................................................... 17 Part 2: Basic Synchronization ....................................................... 19 Synchronization Essentials ........................................................................... 19 Blocking ............................................................................................. 19 Blocking Versus Spinning .................................................................. 20 ThreadState ......................................................................................... 20 Locking ......................................................................................................... 21 Monitor.Enter and Monitor.Exit ......................................................... 22 Choosing the Synchronization Object ................................................ 23 When to Lock ..................................................................................... 23 Locking and Atomicity ....................................................................... 24 Nested Locking ................................................................................... 24 Deadlocks ........................................................................................... 25 Performance ........................................................................................ 26 Mutex .................................................................................................. 26 Semaphore .......................................................................................... 27 © 2006-2010 Joseph Albahari, O’Reilly Media, Inc. All rights reserved. www.albahari.com/threading/ 1 Thread Safety ................................................................................................ 28 Thread Safety and .NET Framework Types ....................................... 28 Thread Safety in Application Servers ................................................. 30 Rich Client Applications and Thread Affinity ................................... 30 Immutable Objects .............................................................................. 32 Signaling with Event Wait Handles .............................................................. 33 AutoResetEvent .................................................................................. 33 ManualResetEvent .............................................................................. 37 CountdownEvent ................................................................................ 38 Creating a Cross-Process EventWaitHandle ...................................... 39 Wait Handles and the Thread Pool ..................................................... 39 WaitAny, WaitAll, and SignalAndWait ............................................. 40 Synchronization Contexts ............................................................................. 41 Reentrancy .......................................................................................... 43 Part 3: Using Threads .................................................................... 44 The Event-Based Asynchronous Pattern ...................................................... 44 BackgroundWorker ....................................................................................... 45 Using BackgroundWorker .................................................................. 45 Subclassing BackgroundWorker ........................................................ 47 Interrupt and Abort ....................................................................................... 48 Interrupt .............................................................................................. 49 Abort ................................................................................................... 49 Safe Cancellation .......................................................................................... 50 Cancellation Tokens ........................................................................... 51 Lazy Initialization ......................................................................................... 52 Lazy<T> ............................................................................................. 53 LazyInitializer..................................................................................... 53 Thread-Local Storage ................................................................................... 54 [ThreadStatic] ..................................................................................... 54 ThreadLocal<T> ................................................................................. 55 GetData and SetData .......................................................................... 55 Timers ........................................................................................................... 56 Multithreaded Timers ......................................................................... 56 Single-Threaded Timers ..................................................................... 58 Part 4: Advanced Topics ............................................................... 59 Nonblocking Synchronization ...................................................................... 59 Memory Barriers and Volatility ......................................................... 59 Interlocked .......................................................................................... 63 Signaling with Wait and Pulse ...................................................................... 65 How to Use Wait and Pulse ................................................................ 65 Producer/Consumer Queue ................................................................. 67 Wait Timeouts .................................................................................... 70 Two-Way Signaling and Races .......................................................... 71 Simulating Wait Handles .................................................................... 72 Writing a CountdownEvent ................................................................ 74 Thread Rendezvous ............................................................................ 75 © 2006-2010 Joseph Albahari, O’Reilly Media, Inc. All rights reserved. www.albahari.com/threading/ 2 The Barrier Class .......................................................................................... 75 Reader/Writer Locks ..................................................................................... 77 Upgradeable Locks and Recursion ..................................................... 78 Suspend and Resume .................................................................................... 80 Aborting Threads .......................................................................................... 80 Complications with Thread.Abort ...................................................... 82 Ending Application Domains ............................................................. 83 Ending Processes ................................................................................ 84 Part 5: Parallel Programming ........................................................ 85 Parallel Programming ................................................................................... 85 Why PFX? .................................................................................................... 85 PFX Concepts ..................................................................................... 86 PFX Components................................................................................ 86 When to Use PFX ............................................................................... 87 PLINQ ........................................................................................................... 87 Parallel Execution Ballistics ..............................................................