Multithreaded Program:
A program that contains two or more threads and these
threads are capable of running concurrently. The multithreading is one of the
specialized from of multitasking.
What is thread?
A thread is a smaller group of codes
in a program and every thread in a program defines a different path of
execution.
Multitasking:
The mechanism by which two or more tasks are carried
out concurrently in a system is called multitasking.
The
multitasking can be subdivided into two as mentioned below
1. Process-Based Multitasking.
2. Thread-Based Multitasking.
Process-Based multitasking allows a
system to run two or more tasks simultaneously. For example, consider your PC
with windows XP, 7 or 8 OS, in which it is possible to listen to song using the
media player and simultaneously play games or chat with your friends by using
messengers like yahoo, etc. You can run all this software simultaneously
because Windows OS installed in your PC supports multitasking.
Note: In process-based multitasking, a
program is the smallest unit of code that will be dispatched.
In Thread-Based
multitasking environment, a program can do two or more tasks
simultaneously. For example consider MS Word text editor where you can edit
text or format text and print the document simultaneously. This is possible
because text editing is carried out by one thread and printing action is
carried out by the other thread.
Note: In thread-based multitasking, the
thread is the smallest unit of code that will be dispatched.
The thread-based
and process-based multitasking are distinguished in the below table.
|
Process-Based
|
Thread-Based
|
|
More overhead
|
Less overhead
|
|
Processes are heavy weight tasks.
They require their own separate address space
|
Threads are light weight tasks.
They will share the same address space and also the same heavy weight process
|
|
The inter-process communication is
limited and expensive
|
The inter-thread communication is
not expensive
|
|
The context switching between
processes is costly.
|
The context switching between
threads is easy and low cost.
|
Threads in Java:
The Java is
designed so that it supports multithreading efficiently. The Java’s run-time
system depends on thread to do many tasks.
In Java, if a
thread stops its execution then no harm is caused to the other part of the
program. The thread in Java can be in any of the below mentioned states.
1. Running state
2. Ready to run state
3. Resumed state
4. Suspended state
5. Blocked state
6. Terminated
Each thread in Java can be given
priority. The thread priorities are integer
that decides, how threads have to be treated with respect to one another.
Thread priority
are used to decide when to switch a thread from the next thread. This switching
of thread is called context switching.
When context switching takes place?
In the below mentioned conditions the context switching takes
place.
1. A thread can voluntarily surrender
control.
2. A thread can be preempted by a
high-priority thread.
3. The threads having same priority will
create a little complexity. In OS like windows, the threads of same priority
are time sliced & handled in round-robin way. In other OS equal priority
threads must voluntarily give up control to their peer threads.
Note: In Java, the
integer values of minimum and maximum priority of threads are 1 and 10
respectively. The default value of thread in Java is 5.
How to implement threads in Java?
In two ways you can implement threads in Java.
1. By extending Thread class.
2. By implementing Runnable interface.
The thread class defines several methods. The below table
list some of the important methods defined by thread class.
|
Method
|
|
currentThread
|
|
getName
|
|
getPriority
|
|
isAlive
|
|
join
|
|
run
|
|
sleep
|
|
Start
|
