A thread is defined as the execution path of a program. Each
thread defines a unique flow of control. If your application involves
complicated 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 lightweight 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 application.
So far we wrote the programs where a single thread runs as a single process which is the running instance of the application. However, this way the application can perform one job at a time. To make it execute more than one task at a time, it could be divided into smaller threads.
Following are the various states in the life cycle of a 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:
The following table shows some of the most commonly used methods of the Thread class:
The following program demonstrates the concept:
The following example demonstrates the use of the sleep() method for making a thread pause for a specific period of time.
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:
Threads are lightweight 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 application.
So far we wrote the programs where a single thread runs as a single process which is the running instance of the application. However, this way the application can perform one job at a time. To make it execute more than one task at a time, it could be divided into smaller threads.
Thread Life Cycle
The life 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 life 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 individual threads in a multithreaded application. 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 MultithreadingApplication { 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:Property | Description |
---|---|
CurrentContext | Gets the current context in which the thread is executing. |
CurrentCulture | Gets or sets the culture for the current thread. |
CurrentPrinciple | Gets or sets the thread's current principal (for role-based security). |
CurrentThread | Gets the currently running thread. |
CurrentUICulture | Gets or sets the current culture used by the Resource Manager to look up culture-specific resources at run-time. |
ExecutionContext | Gets an ExecutionContext object that contains information about the various contexts of the current thread. |
IsAlive | Gets a value indicating the execution status of the current thread. |
IsBackground | Gets or sets a value indicating whether or not a thread is a background thread. |
IsThreadPoolThread | Gets a value indicating whether or not a thread belongs to the managed thread pool. |
ManagedThreadId | Gets a unique identifier for the current managed thread. |
Name | Gets or sets the name of the thread. |
Priority | Gets or sets a value indicating the scheduling priority of a thread. |
ThreadState | Gets a value containing the states of the current thread. |
Sr.No. | Methods |
---|---|
1 |
public void Abort()
Raises a ThreadAbortException in the thread on which it is invoked,
to begin the process of terminating the thread. Calling this method
usually terminates the thread. |
2 |
public 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 |
public 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 |
public 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 application domain. |
5 |
public 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 |
public 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 limited
to the current task. |
7 |
public 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 |
public static void FreeNamedDataSlot(string name)
Eliminates 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 |
public 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 |
public static AppDomain GetDomain()
Returns the current domain in which the current thread is running. |
11 |
public static AppDomain GetDomain()
Returns a unique application domain identifier |
12 |
public 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 |
public void Interrupt()
Interrupts a thread that is in the WaitSleepJoin thread state. |
14 |
public void Join()
Blocks the calling thread until a thread terminates, while continuing
to perform standard COM and SendMessage pumping. This method has
different overloaded forms. |
15 |
public 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 |
public static void ResetAbort()
Cancels an Abort requested for the current thread. |
17 |
public 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 |
public void Start()
Starts a thread. |
19 |
public static void Sleep(int millisecondsTimeout)
Makes the thread pause for a period of time. |
20 |
public static void SpinWait(int iterations)
Causes a thread to wait the number of times defined by the iterations parameter |
21 |
public static byte VolatileRead(ref byte address) public static double VolatileRead(ref double address) public static int VolatileRead(ref int address) public 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 |
public static void VolatileWrite(ref byte address,byte value) public static void VolatileWrite(ref double address, double value) public static void VolatileWrite(ref int address, int value) public 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 |
public static bool Yield()
Causes the calling 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 MultithreadingApplication { class ThreadCreationProgram { public 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 MultithreadingApplication { class ThreadCreationProgram { public static void CallToChildThread() { Console.WriteLine("Child thread starts"); // the thread is paused for 5000 milliseconds 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 MultithreadingApplication { class ThreadCreationProgram { public static void CallToChildThread() { try { Console.WriteLine("Child thread starts"); // do some work, like 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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