How To Thread Inc Sharp

Dot Net Threading, Part I by Randy Charles Morin Page 1 of 16

Intermediate Level

This article is written for the intermediate and senior C# developer. Working knowledge of the C# programming language and Dot Net framework is assumed. The article was written with a Beta version of VS.NET and associated documentation. Changes, although not anticipated, might occur before final release of VS.NET that invalidates portions of this article.

Creating Threads Creating a thread in C# is close to trivial, but not quite. The only non-trivial thing about creating a thread is Dot Net delegateclasses. Let me explain in few words what is a delegate class. The delegate is a wrapper around a code construct in the Dot Net. The code construct could be an object instance, an instance method or a static method. Delegates are used when you want to pass one of the three code constructs as a parameter to another method. When creating a new thread you have to use the ThreadStart delegate class to wrap the instance method that will be executed in the newly created thread. The instance method must return void and must not have any parameters. void ThreadStart() To create a new thread, first create a new ThreadStart object, passing the instance method of the thread procedure in the constructor. The new delegate object is then passed to the constructor of the Thread. Thread thread = new Thread (new ThreadStart (obj.ThreadStart)); You’ve now created a new thread, but the thread is not yet started. To start the thread, you call the Thread.Start instance method. thread.Start(); And that’s it. You have a new running thread. A complete console application that creates a thread and outputs a couple messages to the console window is shown in Listing 1.

Listing 1: Creating Threads using System; using System.Threading; namespace ConsoleApplication1 {  class Class1  {     static void PrintHelloFromThreadName() {   Console.WriteLine("Hello, from thread {0}", Thread.CurrentThread.Name); // {0} }     public void ThreadStart() {   PrintHelloFromThreadName(); }      static void Main(string[] args) {   Thread.CurrentThread.Name = "Main thread";   Class1 obj = new Class1();   Thread thread = new Thread( new ThreadStart(obj.ThreadStart));

Dot Net Threading, Part I by Randy Charles Morin Page 2 of 16   thread.Name = "Forked thread";   thread.Start();   PrintHelloFromThreadName(); }    } }

A nice feature of Dot Net threads, and for that matter any Dot Net object, is the ability name the object. If you name your threads, then the debugger will pick up those names and you’ll have a much easier time debugging (see Figure 1). The frame in the bottom left of the IDE window in Figure 1 shows all the threads in out C# application. I set a breakpoint in the PrintHelloFromThread Name static method in Listing 1 and ran the application. When the application stops on the breakpoint, I called up the threads window from the menu bar, Debug | Window | Threads. As you can see, the Name in the threads window of the IDE is the same as the name given the Thread object in our C# code.

Thread Pools I was very impressed when I found out that the Dot Net framework library included the “System.Threading.ThreadPool” class. I was also impressed by how easy it was to use. You need not create the pool of threads, nor do you have to specify how many consuming threads you require in the pool. The ThreadPool class handles the creation of new threads and the distribution of the wares to consume amongst those threads. You can kick off a consuming thread pool by simply invoking the ThreadPool.QueueUserWorkItem static method. ThreadPool.QueueUserWorkItem( new WaitCallback(Consume), ware);

Ware: For the rest of this article I define a ware to be an item that is produced by the producing thread and consumed by a consuming thread in the consumer producer design pattern. This is a very narrow definition of the word, but one that suits this article. The parameters of the QueueUserWorkItem static method are the WaitCallback delegate that wraps the instance method used in consuming your ware and the ware that you are passing to the method. Your consuming instance method must return void and take one object parameter. The ware that is passed to the QueueUserWorkItem method will be passed into your consuming instance method as the one object parameter. public void Consume(Object obj) Again, the simplicity of C# and the Dot Net framework shine through. In just a few lines of code, I’ve recreated a multithreaded consumer-producer application (see Listing 2).

Listing 2: Creating Thread Pools using System; using System.Threading; using System.Diagnostics; namespace ConsoleApplication2 {   public class Ware  {    public int id;    public Ware(int _id) {

Dot Net Threading, Part I by Randy Charles Morin Page 3 of 16   id = _id; }  }  class Class1  {    public int QueueLength;    public Class1()     {       QueueLength = 0;     }    public void Produce(Ware ware)     {        ThreadPool.QueueUserWorkItem(new WaitCallback(Consume), ware);        QueueLength++;     }    public void Consume(Object obj)     {       Console.WriteLine("Thread {0} consumes {1}",       Thread.CurrentThread.GetHashCode(), //{0}((Ware)obj).id); //{1}       Thread.Sleep(100);       QueueLength­­;     }        public static void Main(String[] args)     {       Class1 obj = new Class1();       for (int i = 0; i < 1000; i++)  {    obj.Produce(new Ware(i));  }       Console.WriteLine("Thread {0}",       Thread.CurrentThread.GetHashCode() ); //{0}       while (obj.QueueLength != 0)        {          Thread.Sleep(1000);        }     }   } } I added the line Thread.Sleep(100) in the Consume method to simulate the processing that a consumer would normally have performed on the ware. If I didn’t include this Sleep’ing, then one consumer thread could have handled all 100 wares. The additional Sleep’ing forces the Dot Net framework to create additional threads and more accurately portrays the features of the ThreadPool class.

Dot Net Threading, Part I by Randy Charles Morin Page 4 of 16

Synchronization Objects

The previous code contains some rather inefficient coding when the main thread cleans up. I repeatedly test the queue length every second until the queue length reaches zero. This may mean that the process will continue executing for up to a full second after the queues are finally drained. Wow! I can’t have that. OK! Maybe that’s not a good reason to change the code, but it is a convenient excuse for me to introduce you to the System.Threading.ManualResetEvent class. Using a ManualResetEvent object, I could trigger the main thread to complete as soon as the last ware was consumed. I’ll do this by creating two new instance data members, a bool WaitForComplete to tell us when the main thread is waiting to exit and a ManualResetEvent Event object that will signal the main thread to exit (see Listing 3).

Listing 3: Using Events private bool WaitForComplete; private ManualResetEvent Event; public void Wait()  {    if (QueueLength == 0)     {       return;     }   Event = new ManualResetEvent(false);   WaitForComplete = true;   Event.WaitOne();  } public void Consume(Object obj)  {    Console.WriteLine("Thread{0}consumes {1}",Thread.CurrentThread.GetHashCode(), //{0}((Ware)obj).id); //{1}    Thread.Sleep(100);    QueueLength­­;    if (WaitForComplete)     {       if (QueueLength == 0)         {           Event.Set();         }     };   } When the consuming thread finishes consuming a ware and detects that the WaitForComplete is true, it will trigger the Event when the queue length is zero. Instead of calling the while block when it wants to exit, the main thread calls the Wait instance method. This method sets the WaitForComplete flag and waits on the Event object. Let me test your threading prowess. The previous listing contained a race condition. Can you find it? Take a minute or two before continuing. Tic! Tic! Tic!

Race Condition A race condition is a bug caused by an incorrect assumption as to the timing of two events, that is, that one event would always occur before the other. The race condition occurs when the system shuts down. If the main thread is swapped out in the Wait instance method between testing if the queue length is zero and setting the WaitForComplete flag to true and then the last

Dot Net Threading, Part I by Randy Charles Morin Page 5 of 16 consuming thread exits the Consume instance method while the main thread is in this state, the event will never be triggered. I ran the code a few hundred times and was never able to trigger the condition. You can’t reproduce it because the main thread should be waiting on the event object well before the last consuming-thread exits.

Monitor and Lock I could have arranged the code otherwise to prevent this race condition, but now I’ve created another opportunity to introduce you to the System.Threading.Monitor class and the lock C# construct. The monitor design pattern is most familiar to Java developers. In Java, the synchronized keyword allowed the developer to create quick critical sections within their code. The Java construct was often called a monitor. The Dot Net framework presents a similar class called the Monitor that implements traditional wait and signal methods called Wait and Pulse. The C# compiler uses this Monitor class to implement a language construct called a lock. The lock is established on an object and while the lock is established, nobody else can acquire the lock and must wait till the lock is freed. I used this lock construct to prevent our previous race condition (see Listing 4).

Listing 4: Using Monitors public void Wait()   {     lock (this)      {         if (QueueLength == 0)           {              return;           }         Event = new ManualResetEvent(false);         WaitForComplete = true;      }     Event.WaitOne();    } public void Consume(Object obj)    {        Console.WriteLine("Thread {0} consumes {1}",Thread.CurrentThread.GetHashCode(), //{0}                        ((Ware)obj).id); //{1}        Thread.Sleep(100);        lock (this)           {              QueueLength­­;              if (!WaitForComplete)                 {                   return;                 }           }        if (QueueLength == 0)           {              Event.Set();           };

Dot Net Threading, Part I by Randy Charles Morin Page 6 of 16   }

Preventing the concurrent setting and testing of the queue length and WaitForComplete flag by two different threads removes the race condition. The lock ensures that the setting and testing of these two variables is essentially atomic.

Join Before Dot Net, I was often asked questions about how to wait for a Win32 thread to exit. The solution was to acquire a handle to the thread and wait on the handle. Or alternatively, you could setup an event that was triggered at the end of the thread and wait on that event. Dot Net provides us with a simpler method of doing the same. If you call the Thread.Join instance method, then the current thread will wait until the thread represented by the Thread object is terminated (see Listing 5).

Listing 5: Using Join using System; using System.Threading; using System.Diagnostics; namespace ConsoleApplication7 {   class Class1    {      public void Pump()        {          for (int i=0;i<100;i++)            {              Console.WriteLine("Value {0}", i);              Thread.Sleep(1);

Dot Net Threading, Part I by Randy Charles Morin Page 7 of 16            }         }     static void Main(string[] args)        {           Class1 obj = new Class1();           Thread pump = new Thread(new ThreadStart(obj.Pump));           pump.Start();           Thread.Sleep(500); // force the other thread          // thru a couple iterations          pump.Join(); // wait until the thread is completed          Console.WriteLine("Goodbye");       }    } } In this previous listing, the main thread creates a new thread (pump), then waits for the thread to complete by calling the pump.Join instance method. If you run the previous code, as is, then the output will be the numbers 0 to 99 and finally the word Goodbye. If you remove the call to pump.Join, then the Goodbye message may be printed before the last number. I chose to put the main thread to sleep for half a second as this displayed the Goodbye message in the middle of the stream of numbers (when pump.Join was removed).

AutoResetEvent & Timer Early in the article, I introduced you to the ManualResetEvent class. This class allowed you to set and reset (signal and unsignal) the event by calling the Set and Reset instance methods. The System.Threading.AutoResetEvent class is very similar to the ManualResetEvent class, but when a thread waiting on the event is signaled, the one thread is released and the event is returned to the unsignaled state. This removes the necessity to reset the signal after a thread is signaled. Another great class in the System.Threading namespace is the Timer class. This class allows you to signal an event at a particular interval in time in the future. The Timer class is implemented using a delegate callback instance method. When the Timer is signaled, the class calls the instance method that you specified in the constructor of the Timer object. The Timer callback can also receive a parameter object passed in the call to the Timer constructor. Presented in Listing 6 is a small sample using the AutoResetEvent and Timer classes.

Listing 6: AutoResetEvent and Timer Class using System; using System.Threading; namespace ConsoleApplication8 {   class Class1     {                public void TimerCallback(Object obj)           {              Console.WriteLine("Timer triggered");              ((AutoResetEvent)obj).Set();              Thread.Sleep(1000);              ((AutoResetEvent)obj).Set();           }

Dot Net Threading, Part I by Randy Charles Morin Page 8 of 16        static void Main(string[] args)          {              Class1 obj = new Class1();              AutoResetEvent ev = new AutoResetEvent(false);              Timer timer = new Timer(new TimerCallback(obj.TimerCallback), ev, 1000, 0);              ev.WaitOne();              Console.WriteLine("Event Fired");              ev.WaitOne();              Console.WriteLine("Event Fired");         }     } } Note that the Timer callback instance method is wrapped in a TimerCallback delegate object. The main thread will create an AutoResetEvent object and a Timer object. The main thread then waits on the event object. The TimerCallback instance method is called after one second, triggering the event object. Because the event object is automatically reset, when the main thread attempts to wait on the event again, the thread yields until the event is signaled a second time. The TimerCallback instance method waits another second and then signals the event a second time, releasing the main thread.

ReaderWriterLock Another popular design pattern introduced as a class in the Dot Net framework is the ReaderWriterLock. This class allows an unlimited amount of read locks or one write lock, but not both. This allows anyone to read the protected resource, as long as nobody is writing to the protected resource and allows only one thread to write to the protected resource at any one time. Listing 1 presents a sample using the ReaderWriterLock class.

Listing 1: ReaderWriterLock Class using System; using System.Threading; namespace ConsoleApplication9 { class Class1   {     public Class1() { rwlock = new ReaderWriterLock(); val = "Writer Sequence Number is 1"; }     private ReaderWriterLock rwlock;    private string val;    public void Reader() { rwlock.AcquireReaderLock(Timeout.Infinite); Console.WriteLine("Acquired Read Handle: " "Value = {0}", val); Thread.Sleep(1); Console.WriteLine("Releasing Read Handle");

Dot Net Threading, Part I by Randy Charles Morin Page 9 of 16 rwlock.ReleaseReaderLock(); } public void Writer() { rwlock.AcquireWriterLock(Timeout.Infinite); Console.WriteLine("Acquired Write Handle"); int id = rwlock.WriterSeqNum; Console.WriteLine("Writer Sequence Number is {0}", id); Thread.Sleep(1); val = "Writer "; Thread.Sleep(1); val += "Sequence "; Thread.Sleep(1); val += "Number "; Thread.Sleep(1); val += "is "; Thread.Sleep(1); val += id; Console.WriteLine("Releasing Write Handle"); rwlock.ReleaseWriterLock(); } static void Main(string[] args) { Class1 obj = new Class1(); const int n = 1000; Thread[] reader = new Thread[n]; Thread[] writer = new Thread[10]; for (int i=0;i
Dot Net Threading, Part I by Randy Charles Morin Page 10 of 16 In the above listing, I create 10 writer threads and 1000 reader threads. I parameterized the number of reader threads so that I could quickly trigger different behaviors in the code by modifying the number of reader threads. Once the threads are started they attempt to acquire read and write lock on the ReaderWriterLock object. If you run the code, then you can see the writer threads have a difficult time acquiring write locks. I tried to put as many small sleep statements as I could to force the threads to swap out of memory earlier than they would have normally.

Mutex The last synchronization object I’ll present here is the Mutex. The most useful feature of the Mutex class is that it may be named. This allows you to create two Mutex objects in different areas of code without having to share Mutex object instances. As long as the Mutex object instances have the same name, they will synchronize with each other. You could create the Mutex in two different processes on the same machine and the synchronization crosses the process boundary. Nor do you have to worry about passing the Mutex object in order to share the synchronization object between two threads or methods (see Listing 2).

Listing 2: Mutex Class using System; using System.Threading; namespace ConsoleApplication10 {   class Class1    {       public void ThreadStart() { Mutex mutex = new Mutex(false, "MyMutex"); mutex.WaitOne(); Console.WriteLine("Hello"); } static void Main(string[] args) {   Class1 obj = new Class1();   Thread thread = new Thread( new ThreadStart(obj.ThreadStart));   Mutex mutex = new Mutex(true, "MyMutex");   thread.Start();   Thread.Sleep(1000);   Console.WriteLine("Signal");   mutex.ReleaseMutex();         }     } } In the above listing, two separate Mutex objects are created, but the Mutex class allows the two instances to interact. The Signal will always precede the Hello in the output of this program. This is because the Mutex in the thread is created with the lock acquired. The second thread then creates the Mutex without acquiring the lock. The second thread will then wait on the mutex until the main thread releases the mutex a second later.

Thread Local Storage The Thread class and System.Threading namespace also contain some methods and classes for realizing thread local storage. Thread local storage is a manner of storing data in a container that is unique to the thread. Many threads could then use the same named container to store their data without concern of collision. Each thread’s local storage is distinct from another

Dot Net Threading, Part I by Randy Charles Morin Page 11 of 16 thread’s local storage and is only available in the one thread. Listing 3 shows a small sample using the thread-local-storage methods and classes.

Listing 3: Thread Local Storage using System; using System.Threading; namespace ConsoleApplication11 { class Class1   {      public void ThreadStart()        {           string str1 = "My Cookie " + Thread.CurrentThread.GetHashCode();           Console.WriteLine("worker thread: {0}",str1);           LocalDataStoreSlot lds = Thread.GetNamedDataSlot("COOKIE");           Thread.SetData(lds, str1); Thread.Sleep(1); LocalDataStoreSlot lds2 = Thread.GetNamedDataSlot("COOKIE"); string str2 = ""; str2 = (string)Thread.GetData(lds2); Console.WriteLine("worker thread: {0}",str2);       }      static void Main(string[] args) { string str1 = "My Cookie " + Thread.CurrentThread.GetHashCode(); Console.WriteLine("main thread: {0}", str1); LocalDataStoreSlot lds = Thread.AllocateNamedDataSlot("COOKIE"); Thread.SetData(lds, str1); Class1 obj = new Class1(); Thread thread = new Thread( new ThreadStart(obj.ThreadStart)); thread.Start(); Thread.Sleep(1); LocalDataStoreSlot lds2 = Thread.GetNamedDataSlot("COOKIE"); string str2 = ""; str2 = (string)Thread.GetData(lds2); Console.WriteLine("main thread: {0}", str2); } } }

You could also create and start more than one thread and the behavior of the thread local storage becomes more obvious. I have played with Win32 thread-local-storage functions and created my own for portability to UNIX, but I have rarely found them very useful. I strongly believe in stateless computing and thread-local-storage contradicts this belief.

COM Interoperability

Dot Net Threading, Part I by Randy Charles Morin Page 12 of 16 Now what about those COM apartments? How do these new Dot Net threads handle COM apartments? Dot Net threads can reside in both single and multithreaded apartments. When a Dot Net thread is first started it exists neither in a single-threaded or multithreaded apartment. A static state variable Thread.CurrentThread.Apartment indicates the current apartment type. If you run the code in Listing 4, then the apartment type will be Unknown, as the thread would not have entered an apartment yet.

Listing 4: Threading Model Attributes using System; using System.Threading; namespace ConsoleApplication5 { class Class1 { // line output  // Unknown // [STAThread] // STA // [MTAThread] // MTA public static void Main(String[] args) {    Console.WriteLine("Apartment State = {0}",Thread.CurrentThread.ApartmentState); } } } If you uncomment the line with the STAThread attribute, then the thread set its ApartmentState to STA. If you uncomment the line with the MTAThread attribute, then the thread set its ApartmentState to MTA. This allows control over the apartment type, similar to CoInitializeEx. You can also set the ApartmentState static member directly (see Listing 5).

Listing 5: ApartmentState using System; using System.Threading; namespace ConsoleApplication6 { class Class1 { static void Main(string[] args) { // Thread.CurrentThread.ApartmentState =  ApartmentState.STA; Thread.CurrentThread.ApartmentState = ApartmentState.MTA; Console.WriteLine("Apartment State = {0}", Thread.CurrentThread.ApartmentState); } } } Setting the ApartmentState property has the same affect as using the STAThread and MTAThread attributes. There are also class attributes that affect the threading model used by the dot Net framework. The ThreadAffinity and Synchronization class attributes can be used to synchronize access to a class and its instance members. [ThreadAffinity()] public class Class1 : ContextBoundObject [Synchronization()] public class Class1 : ContextBoundObject

Dot Net Threading, Part I by Randy Charles Morin Page 13 of 16 When calling into such classes, the calls are serialized to limit access to the class to one thread at any one time. At this point, these class context attributes are really thin on documentation. So, I’ll save a more in-depth explanation that may be incorrect anyway.

Win32 to Dot Net I figured with all this work I’m doing learning Dot Net threads that I would leave you with an important resource. Table 1 shows my attempt in converting Win32 functions to Dot Net classes and methods.

Table 1: Converting Win32 to Dot Net Win32

Dot Net

CreateEvent

new System.Threading.Event

CreateMutex

new System.Threading.Mutex

CreateSemaphore

n/a

CreateThread

new System.Threading.Thread and new System.Threading.ThreadStart

CreateWaitableTimer

new System.Threading.Timer

InitializeCriticalSectiona EnterCriticalSection LeaveCriticalSection DeleteCriticalSection

lock (C#) System.Threading.Monitor

InterlockedCompareExchange

System.Threading.Interlock.CompareExchange

InterlockedDecrement

System.Threading.Interlock.Decrement

InterlockedExchange

System.Threading.Interlock.Exchange

InterlockedIncrement

System.Threading.Interlock.Increment

OpenEvent

n/a

OpenMutex

new System.Threading.Mutex

OpenSemaphore

n/a

OpenWaitableTimer

n/a

PulseEvent ReleaseMutex

n/a System.Threading.Mutex.ReleaseMutex

ReleaseSemaphore

n/a

ResetEvent

System.Threading.AutoResetEvent.Reset or System.Threading.ManualResetEvent.Reset

ResumeThread

System.Threading.Thread.Resume

SetEvent

System.Threading.AutoResetEvent.Set or System.Threading.ManualResetEvent.Set

SetWaitableTimer

n/a

Sleep

System.Threading.Thread.Sleep

SuspendThread

System.Threading.Thread.Suspend

TerminateThread

System.Threading.Thread.Abort

WaitForSingleObject and WaitForSingleObjectEx

System.Threading.Thread.Join or System.Threading.Monitor.Wait or System.Threading.WaitHandle.WaitOne

WaitForMultipleObjects and WaitForMultipleObjects

System.Threading.WaitHandle.WaitAll or System.Threading.WaitHandle.WaitAny

Dot Net Threading, Part I by Randy Charles Morin Page 14 of 16

If you were to undertake a project of converting a Win32 application to a Dot Net application, then this table could prove very useful. In some cases, a few objects and methods in the Dot Net framework could closely emulate a Win32 function. I had to, on occasion, decide how closely they matched and sometimes decided that a match was not appropriate. As an example, you could create a semaphore with a Mutex object and a counter. But I wouldn’t say it’s a close match, so I didn’t mention these instances. In other cases, I had to decide between two matches.

Thread States The last few topics in this article are really just the few bits of reference information I dug up on Dot Net threads. This section describes the states of a thread. The Thread object in the Dot Net framework has a property called the ThreadState, which is one of the members of the following enumeration, which I pulled from the Dot Net documentation. public enum ThreadState { Running = 0, SuspendRequested = 2, Background = 4, Unstarted = 8, WaitSleepJoin = 32, Suspended = 64, AbortRequested = 128, Aborted = 256 }; Unfortunately, I have been able to generate ThreadState’s that are not in this enumeration. Specifically, the Stopped ThreadState seems to be missing and is easy to generate. If you check the state of a thread that has run to completion, then the state is marked as Stopped. What I also found is that it is quite easy to generate dual states. You can be in the AbortRequested state and the WaitSleepJoin state. If you catch the ThreadAbortException and then call Thread.Sleep, then the ThreadState will be “WaitSleepJoin, AbortRequested”, a dual state. The same is true if you are sleeping when the Suspend instance method is called. Immediately after the call to the Suspend instance method, the ThreadState property reports “SuspendRequested, WaitSleepJoin”, then quickly changes to “WaitSleepJoin, Suspended”. I’ve encountered a few state diagrams that tried to depict the state transitions of Dot Net threads. I must say that most are misleading or incomplete. The biggest problem is that most of the state diagrams did not attempt to account for dual states. My own attempt at the state diagram, I know, is still lacking but much further along then anything else I’ve seen (see Figure 1).

Background Threads There is still a lot missing from the state diagram. Specifically, what happens when you Suspend (), Wait (), Join (), Sleep (), Abort() a background thread. I’m not going to confuse the diagram to explain these new states. Rather, let me explain that a thread is either a background thread or a foreground thread. Actions on a background thread are equivalent to actions on a foreground thread, except in one respect, which I will explain in the next paragraph. So, if you attempt to suspend a running background thread, then it will move to the SuspendRequested state, then to the Suspended state and finally back to the Background state, in the same manner as a foreground thread.

Dot Net Threading, Part I by Randy Charles Morin Page 15 of 16

Figure 1: State Diagram The difference between a background thread and a foreground thread is pretty simple. When the last foreground thread of a process is stopped, then the process terminates. There could be zero, 1 or an infinite number of background threads and they have no vote in whether a process terminates or not. So when the last foreground thread stops, then all background threads are also stopped and the process is stopped. I’ve seen quite a few dot-NET programmers incorrectly use the background thread to mean any thread created using the Thread constructor. The terminology is therefore getting very confusing. The correct meaning of background thread in Dot Net framework is a thread that does not have impact on whether a process is terminated.

Thread Safe Objects and Types Here’s a rather interesting tidbit of news. Many of the Dot Net objects and types are thread-safe. The first time I heard that I was rather confused at what it could mean. Does this mean an increment (++) operation on a C# integer is atomic? I put together a small piece of C# code that launched a thousand threads and incremented and decremented one integer a million times per thread. I structured the code to swap the threads like mad to try and create a race condition that would invalidate the operations on the integer. I was unsuccessful in generating incorrect results. So, I assume the operation is atomic. But I don’t have any proof (beyond proof-by-example) that it is an atomic operation.

Interlocked Throughout this article, I have written code that assumes that some operations on C# objects and types are atomic. I would never suggest writing such code in a production environment. In such an environment, you will have to fall back onto our old InterlockedIncrement and InterlockedDecrement friends. In C#, these are in the System.Threading.Interlocked class. The class has two static methods Interlocked.Increment and Interlocked.Decrement. Use them well.

Conclusion

I started this trek into Dot Net threads for one reason. I wanted to evaluate them as a possible alternative for servers that require a lot of thread programming. What I found was that Dot Net’s Threading namespace is by far the easiest way to write

Dot Net Threading, Part I by Randy Charles Morin Page 16 of 16 applications that require a lot of thread programming. I didn’t find any performance problems with the Dot Net threads, but neither did I find them any faster than other thread libraries available in C++ or Java threads.