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C# - Multithreading
  • 时间：2024-11-03

C# - Multithreading

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A thread is defined as the execution path of a program. Each thread defines a unique flow of control. If your apppcation involves comppcated and time consuming operations, then it is often helpful to set different execution paths or threads, with each thread performing a particular job.

Threads are pghtweight processes. One common example of use of thread is implementation of concurrent programming by modern operating systems. Use of threads saves wastage of CPU cycle and increase efficiency of an apppcation.

So far we wrote the programs where a single thread runs as a single process which is the running instance of the apppcation. However, this way the apppcation can perform one job at a time. To make it execute more than one task at a time, it could be spanided into smaller threads.

Thread Life Cycle

The pfe cycle of a thread starts when an object of the System.Threading.Thread class is created and ends when the thread is terminated or completes execution.

Following are the various states in the pfe cycle of a thread −

    The Unstarted State − It is the situation when the instance of the thread is created but the Start method is not called.

    The Ready State − It is the situation when the thread is ready to run and waiting CPU cycle.

    The Not Runnable State − A thread is not executable, when

      Sleep method has been called

      Wait method has been called

      Blocked by I/O operations

    The Dead State − It is the situation when the thread completes execution or is aborted.

The Main Thread

In C#, the System.Threading.Thread class is used for working with threads. It allows creating and accessing inspanidual threads in a multithreaded apppcation. The first thread to be executed in a process is called the main thread.

When a C# program starts execution, the main thread is automatically created. The threads created using the Thread class are called the child threads of the main thread. You can access a thread using the CurrentThread property of the Thread class.

The following program demonstrates main thread execution −

using System;
using System.Threading;

namespace MultithreadingApppcation {
   class MainThreadProgram {
      static void Main(string[] args) {
         Thread th = Thread.CurrentThread;
         th.Name = "MainThread";
         
         Console.WriteLine("This is {0}", th.Name);
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

This is MainThread

Properties and Methods of the Thread Class

The following table shows some most commonly used properties of the Thread class −

Sr.No. Property & Description
1

CurrentContext

Gets the current context in which the thread is executing.
2

CurrentCulture

Gets or sets the culture for the current thread.
3

CurrentPrinciple

Gets or sets the thread s current principal (for role-based security).
4

CurrentThread

Gets the currently running thread.
5

CurrentUICulture

Gets or sets the current culture used by the Resource Manager to look up culture-specific resources at run-time.
6

ExecutionContext

Gets an ExecutionContext object that contains information about the various contexts of the current thread.
7

IsApve

Gets a value indicating the execution status of the current thread.
8

IsBackground

Gets or sets a value indicating whether or not a thread is a background thread.
9

IsThreadPoolThread

Gets a value indicating whether or not a thread belongs to the managed thread pool.
10

ManagedThreadId

Gets a unique identifier for the current managed thread.
11

Name

Gets or sets the name of the thread.
12

Priority

Gets or sets a value indicating the schedupng priority of a thread.
13

ThreadState

Gets a value containing the states of the current thread.

The following table shows some of the most commonly used methods of the Thread class −

Sr.No. Method & Description
1

pubpc void Abort()

Raises a ThreadAbortException in the thread on which it is invoked, to begin the process of terminating the thread. Calpng this method usually terminates the thread.
2

pubpc static LocalDataStoreSlot AllocateDataSlot()

Allocates an unnamed data slot on all the threads. For better performance, use fields that are marked with the ThreadStaticAttribute attribute instead.
3

pubpc static LocalDataStoreSlot AllocateNamedDataSlot(string name)

Allocates a named data slot on all threads. For better performance, use fields that are marked with the ThreadStaticAttribute attribute instead.
4

pubpc static void BeginCriticalRegion()

Notifies a host that execution is about to enter a region of code in which the effects of a thread abort or unhandled exception might jeopardize other tasks in the apppcation domain.
5

pubpc static void BeginThreadAffinity()

Notifies a host that managed code is about to execute instructions that depend on the identity of the current physical operating system thread.
6

pubpc static void EndCriticalRegion()

Notifies a host that execution is about to enter a region of code in which the effects of a thread abort or unhandled exception are pmited to the current task.
7

pubpc static void EndThreadAffinity()

Notifies a host that managed code has finished executing instructions that depend on the identity of the current physical operating system thread.
8

pubpc static void FreeNamedDataSlot(string name)

Epminates the association between a name and a slot, for all threads in the process. For better performance, use fields that are marked with the ThreadStaticAttribute attribute instead.
9

pubpc static Object GetData(LocalDataStoreSlot slot)

Retrieves the value from the specified slot on the current thread, within the current thread s current domain. For better performance, use fields that are marked with the ThreadStaticAttribute attribute instead.
10

pubpc static AppDomain GetDomain()

Returns the current domain in which the current thread is running.
11

pubpc static AppDomain GetDomainID()

Returns a unique apppcation domain identifier
12

pubpc static LocalDataStoreSlot GetNamedDataSlot(string name)

Looks up a named data slot. For better performance, use fields that are marked with the ThreadStaticAttribute attribute instead.
13

pubpc void Interrupt()

Interrupts a thread that is in the WaitSleepJoin thread state.
14

pubpc void Join()

Blocks the calpng thread until a thread terminates, while continuing to perform standard COM and SendMessage pumping. This method has different overloaded forms.
15

pubpc static void MemoryBarrier()

Synchronizes memory access as follows: The processor executing the current thread cannot reorder instructions in such a way that memory accesses prior to the call to MemoryBarrier execute after memory accesses that follow the call to MemoryBarrier.
16

pubpc static void ResetAbort()

Cancels an Abort requested for the current thread.
17

pubpc static void SetData(LocalDataStoreSlot slot, Object data)

Sets the data in the specified slot on the currently running thread, for that thread s current domain. For better performance, use fields marked with the ThreadStaticAttribute attribute instead.
18

pubpc void Start()

Starts a thread.
19

pubpc static void Sleep(int milpsecondsTimeout)

Makes the thread pause for a period of time.
20

pubpc static void SpinWait(int iterations)

Causes a thread to wait the number of times defined by the iterations parameter
21

pubpc static byte VolatileRead(ref byte address)

pubpc static double VolatileRead(ref double address)

pubpc static int VolatileRead(ref int address)

pubpc static Object VolatileRead(ref Object address)

Reads the value of a field. The value is the latest written by any processor in a computer, regardless of the number of processors or the state of processor cache. This method has different overloaded forms. Only some are given above.
22

pubpc static void VolatileWrite(ref byte address,byte value)

pubpc static void VolatileWrite(ref double address, double value)

pubpc static void VolatileWrite(ref int address, int value)

pubpc static void VolatileWrite(ref Object address, Object value)

Writes a value to a field immediately, so that the value is visible to all processors in the computer. This method has different overloaded forms. Only some are given above.
23

pubpc static bool Yield()

Causes the calpng thread to yield execution to another thread that is ready to run on the current processor. The operating system selects the thread to yield to.

Creating Threads

Threads are created by extending the Thread class. The extended Thread class then calls the Start() method to begin the child thread execution.

The following program demonstrates the concept −

using System;
using System.Threading;

namespace MultithreadingApppcation {
   class ThreadCreationProgram {
      pubpc static void CallToChildThread() {
         Console.WriteLine("Child thread starts");
      }
      static void Main(string[] args) {
         ThreadStart childref = new ThreadStart(CallToChildThread);
         Console.WriteLine("In Main: Creating the Child thread");
         Thread childThread = new Thread(childref);
         childThread.Start();
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

In Main: Creating the Child thread
Child thread starts

Managing Threads

The Thread class provides various methods for managing threads.

The following example demonstrates the use of the sleep() method for making a thread pause for a specific period of time.

using System;
using System.Threading;

namespace MultithreadingApppcation {
   class ThreadCreationProgram {
      pubpc static void CallToChildThread() {
         Console.WriteLine("Child thread starts");
         
         // the thread is paused for 5000 milpseconds
         int sleepfor = 5000; 
         
         Console.WriteLine("Child Thread Paused for {0} seconds", sleepfor / 1000);
         Thread.Sleep(sleepfor);
         Console.WriteLine("Child thread resumes");
      }
      
      static void Main(string[] args) {
         ThreadStart childref = new ThreadStart(CallToChildThread);
         Console.WriteLine("In Main: Creating the Child thread");
         
         Thread childThread = new Thread(childref);
         childThread.Start();
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

In Main: Creating the Child thread
Child thread starts
Child Thread Paused for 5 seconds
Child thread resumes

Destroying Threads

The Abort() method is used for destroying threads.

The runtime aborts the thread by throwing a ThreadAbortException. This exception cannot be caught, the control is sent to the finally block, if any.

The following program illustrates this −

using System;
using System.Threading;

namespace MultithreadingApppcation {
   class ThreadCreationProgram {
      pubpc static void CallToChildThread() {
         try {
            Console.WriteLine("Child thread starts");
            
            // do some work, pke counting to 10
            for (int counter = 0; counter <= 10; counter++) {
               Thread.Sleep(500);
               Console.WriteLine(counter);
            }
            
            Console.WriteLine("Child Thread Completed");
         } catch (ThreadAbortException e) {
            Console.WriteLine("Thread Abort Exception");
         } finally {
            Console.WriteLine("Couldn t catch the Thread Exception");
         }
      }
      static void Main(string[] args) {
         ThreadStart childref = new ThreadStart(CallToChildThread);
         Console.WriteLine("In Main: Creating the Child thread");
         
         Thread childThread = new Thread(childref);
         childThread.Start();
         
         //stop the main thread for some time
         Thread.Sleep(2000);
         
         //now abort the child
         Console.WriteLine("In Main: Aborting the Child thread");
         
         childThread.Abort();
         Console.ReadKey();
      }
   }
}

When the above code is compiled and executed, it produces the following result −

In Main: Creating the Child thread
Child thread starts
0
1
2
In Main: Aborting the Child thread
Thread Abort Exception
Couldn t catch the Thread Exception
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