Threads

Threads

What is Thread: A thread is a lightweight sub process, a smallest unit of processing. It is a separate path of execution. It shares the memory area of process.

Multitasking

Multitasking is a process of executing multiple tasks simultaneously. We use multitasking to utilize the CPU. Multitasking can be achieved by two ways:

·         Process-based Multitasking(Multiprocessing)

·   Thread-based Multitasking(Multithreading)

Note: Each processor is independent.

Multithreading

Multithreading is a process of executing multiple threads simultaneously

Achieving multiple threads in single class

1) Process-based Multitasking (Multiprocessing)

Ø Each process have its own address in memory i.e. each process allocates separate memory area. Ø Process is heavyweight. Ø Cost of communication between the process is high. Ø Switching from one process to another require some time for saving and loading registers, memory maps, updating lists etc.

2) Thread-based Multitasking (Multithreading)

·   Threads share the same address space. ·   Thread is lightweight. ·   Cost of communication between the thread is low. ·   At least one process is required for each thread. All programming languages support multithreading Difference :-

Multiprocessing and multithreading, both are used to achieve multitasking.  But we use multithreading than multiprocessing because threads share a common memory area. They don't allocate separate memory area so save memory, and context-switching between the threads takes less time than processes.

Multithreading is mostly used in games, animation etc. Examples : In system opening command window, notepad, eclipse, only attached files there are multiple independent. Every system has won processor that is take care of entire process. Multithreading and explain its application areas Executing several threads simultaneously where each thread is a separate independent part of the same program is called multithreading. Java language provides inbuilt support for multithreading by defining a reach library, classes and interfaces like Thread, Thread Group, Runnable etc. The main important application area of multithreading are video games implementation, animation development, multimedia graphics etc Advantage of Multithreading  : ·         The main advantage of multithreading is reduces response time and improves performance of the system. ·         Java language provides inbuilt support for multithreading by defining a reach library, classes and interfaces like Thread, Thread Group, Runnable etc. But in C++ there is no inbuilt support for multithreading

There two types Threads:

1. User thread

2. Daemon thread

User threads: It is independent thread it’s not dependent on parent thread

User threads continually execute rather than looking for parent thread once assigned task is fully got over then only come again

Daemon thread:

Ø  It is dependent thread its dependent on parent thread.

Ø  The daemon thread is a service provider thread.

Ø  It provides services to the user thread.

Ø  Its life depends on the user threads i.e. when all the user threads dies, JVM terminates this thread automatically

Important points:

• It provides services to user threads for background supporting tasks. It has no role in life than to serve user threads.
• Its life depends on user threads.
• It is a low priority thread.

Thread class: In java there two ways creating threads

Thread class provide constructors and methods to create and perform operations on a thread, Thread class extends Object class and implements Runnable interface. There are two ways to create a thread: By extending Thread class By implementing Runnable interface. While executing java command internally three threads are creating these are The Thread Scheduler: The thread scheduler is the part of the JVM that decides which thread should run. There is no guarantee that which run able thread will be chosen to run by the thread scheduler. Only one thread at a time can run in a single process. The thread scheduler mainly uses preemptive or time slicing scheduling to schedule the threads What is the difference between preemptive scheduling and time slicing? Under preemptive scheduling, the highest priority task executes until it enters the waiting or dead states or a higher priority task comes into existence. Under time slicing, a task executes for a predefined slice of time and then reenters the pool of ready tasks. The scheduler then determines which task should execute next, based on priority and other factors Garbage collector: All abounded objects are removing from the memory in finally. Main() : Its responsible to execute main method .it’s a user thread

Note: Garbage collector and main are registered with thread Scheduler