Multi Threading 3

Multi Threading

Multi Tasking, Multi Processing  

Program :-A sequence of instructions that can be executed by a computer. Multi Tasking :- Multitasking is the ability to execute more than one Program (task) at the same time.

There are two basic types of multitasking: preemptive and cooperative





Preemptive Multitasking :-the operating system divides the CPU time to each program in slices. Cooperative :-cooperative multitasking, each program can control the CPU for as long as it needs it .

OS/2, Windows 95, Windows NT, the Amiga operating system and UNIX use preemptive multitasking, whereas Microsoft Windows 3.x and the MultiFinder (for Macintosh computers) use cooperative multitasking.

Multi Processing Multi Processing :- Multiprocessing is running a system with more than one processor . Multiprocessing can be said to be either asymmetric or symmetric Asymmetric :-Asymmetric multiprocessing designates some processors to perform system tasks only, and others to run applications only. Symmetric :- [SMP] Symmetric multiprocessing, often abbreviated SMP, allows either system or user tasks to run on any processor. 

Multi Threading Each application/program that is running on a system is a process. (Set of some code.) Again within the main Process more than one sub process can be divided those can be given specific processor time to do the allocated task. The sub processes having their own execution path can be defined as a thread. An ability of programming witch supports to create more than one thread within a single application (process) called as Multi threading.

Multithreading is a powerful tool for creating high performance applications, especially those that require a great user interaction,Data base interaction, Networking interaction… Tasks those should be handled using Multithreading:  

Printing Asynchronous Connection Asynchronous Query etc.

As an Example :- MS Word Application. more than one task as printing,Editing,Editing and many more can be performed at a time using multithreading.

Program2

1 Sec.

½ Sec.

--------

½ Sec.

2 Sec.

---------

Program1 ---------

1 Sec.

O/S

Processor

Multithreading in . NET

.NET Runtime (CLR) is maintaining a service called as Thread-Support that enables .NET application to divide into more than one Threads.

System.Threading Namespace Thread Class ThreadStart Delegate task1() task2() ThreadStart ts1=new ThreadStart(task1) ThreadStart ts2=new ThreadStart(task2) Thread t1=new Thread(ts1) Thread t2=new Thread(ts2) Note:- Delegate is nothing but like a Function Pointer. In VB.NET ThreadStart(AddressOf ts1)

Basic Example of Thread using VB and Csharp [Console Application]

Advantage of Multi Threading 

Improved responsiveness :-If the

application is performing operations that take a perceivably long time to complete, these operations can be put into a separate thread which will allow the application to continue to be responsive to the user.



Faster application :-if there are a number of calculations to be performed or the contents of a file are being processed, then there the application can be made faster by performing multiple operations at the same time.



Prioritization :-Threads can be assigned a

priority which would allow higher priority tasks to take precedence over lower priority tasks

.



Disadvantage of Multiple Thread Programming and debugging is more complex :-With multithreaded applications

there is always a risk of Deadlocks and Debugging of an application becomes more difficult. 

Threads add overhead to the system :-

To maintain a track of the large number of threads,obviously going to consume processor time. If there are too many threads then each thread may not be given sufficient time to execute.In addition, each thread is scheduled for execution less frequently due to the volume and time slice committed to each thread.

II Example of Thread [Windows Application]

Life Cycle of Thread Sleep

Thread

Start

Suspend Abort

Wakeups

Resume

       

Members of Thread Class Start() :- To start a particular Thread. **Sleep(m.sec.) :-To rest a thread for specified duration. Suspend() :-To halt a thread until explicitly resumed. Resume() :-To restart execution of a suspended thread. Abort() :-To stop a running thread execution permanently . **Currentthread:-Returns the thread currently running. ThreadState:-Returns the state of the threadrunning,suspended… Priority:- Specifies a priority of a thread.

Note:- ** Shared or Static Member.

III Example to implement other methods and events of thread.

synchronize access to resources in multithreaded applications.

Since each thread executes asynchronously in a multithreaded application. The asynchronous nature of threads must be coordinated means that access to resources such as file handles, network connections, and memory. Otherwise, two or more threads could access the same resource at the same time, each unaware of the other's actions. The result is unpredictable data corruption.

The lock keyword can be used to ensure that a block of code runs to completion without interruption by other threads. A lock statement begins with the keyword lock, which is given an object as an argument, and followed by a code block that is to be executed by only one thread at a time. public void Function(){ Object lockThis = new Object(); lock(lockThis) { // Access thread-sensitive resources. } }

VB.NET Private Sub f1() SyncLock ("updating_f1.txt") ‘Code to handle a particular file End SyncLock End Sub

Thread ThreadStart

Class Delegate

task1() task2() ThreadStart ts1=new ThreadStart(task1) ThreadStart ts2=new ThreadStart(task2)

Setting Priority to a particular Thread Thread t1=new Thread(ts1) Thread t2=new Thread(ts2)

t1.Priority=ThreadPriority.Lowest Note:- Delegate is nothing but like Normal a Function Pointer. In VB.NET ThreadStart(AddressOfHighest ts1) Basic Example of Thread using