Introduction - Multitasking

Multitasking

Multitasking is performing two or more tasks at the same time. Nearly all operating systems are capable of multitasking by using one of two multitasking techniques:

1. process-based multitasking

2. thread-based multitasking.

Process-based multitasking is running two programs concurrently. Programmers refer to a program as a process. Therefore, you could say that process-based multitasking is program-based multitasking. For example, process-based multitasking enables you to run the Java compiler at the same time that you are using a text editor. In process-based multitasking, a program is the smallest unit of code that can be dispatched by the scheduler.

In a thread-based multitasking environment, the thread is the smallest unit of dispatchable code. This means that a single program can perform two or more tasks simultaneously. For instance, a text editor can format text at the same time that it is printing, as long as these two actions are being performed by two separate threads.

Each thread is scheduled by the operating system for specific time depending upon the OS. Suppose there are three thread tl , t2, t.3. Scheduler takes any thread to run first and. run it for some time. After its time slice completes scheduler switches to other thread. If any thread is not completed in its time slice then it can get CPU again. in which order threads will run is not fix. It depends on the scheduler.Multitasking enables you to write very efficient programs that make maximum use of the CPU , because idle time can be keep  a minimum.

Difference between MultiProcessing and MultiThreading

A good way to remember the difference between process-based multitasking and thread-based multitasking is to think of process-based as working with multiple programs and thread-based as orking with parts of one program. Thus, process-based multitasking deals with the “big picture,” and thread-based multitasking handles the details.

Multitasking threads require less overhead than multitasking processes. Processes are heavyweight tasks that require their own separate address spaces. Interprocess communication is expensive and limited. Context switching from one process to another is also costly. Threads, on the other hand, are lightweight. They share the same address space and cooperatively share the same heavyweight process. Interthread communication is inexpensive, and context switching from one thread to the next is low cost. While Java programs make use of process-based multitasking environments, process-based multitasking is not under the control of Java. 

Posted by : Ruchita Pandya