Priorities

Priorities

. • In Java threads scheduler selects the threads using their priorities.

• The thread priority is a simple integer value that can be assigned to the particular thread.

• These priorities can range from 1 (lowest priority) to 10 (highest priority).

• There are two commonly used functionalities in thread scheduling -

o setPriority

o getPriority

• The function setPriority is used to set the priority to each thread

Thread_Name.setPriority (priority_val);

Where, priority_val is a constant value denoting the priority for the thread. It is defined as follows

1. MAX_PRIORITY = 10

2. MIN_PRIORITY = 1

3. NORM_PRIORITY = 5

• The function getPriority is used to get the priority of the thread.

Thread_Name.getPriority();

What is Preemption?

• Preemption is a situation in which when the currently executed thread is suspended temporarily by the highest priority thread.

• The highest priority thread always preempts the lowest priority thread.

Let us see the illustration of thread prioritizing with the help of following example

Java program[Thread_PR_Prog.java]

class A extends Thread

{

public void run()

{

System.out.println("Thread #1");

for(int i=1;i<=5;i++)

{

System.out.println("\tA: "+i)

}

System.out.println("\n-----End of Thread #1-------");

}

}

class B extends Thread

{

public void run()

{

System.out.println("Thread #2");

for(int k=1;k<=5;k++)

{

System.out.println("\tB: "+k);

}

System.out.println("\n-----End of Thread #2-------");

}

}

class Thread_PR_Prog

{

public static void main(String[] args)

{

A obj1=new A();

B obj2=new B();

obj1.setPriority(1);

obj2.setPriority(10);//highest priority

System.out.println("Strating Thread#1");

obj1.start();

System.out.println("Strating Thread#2");

obj2.start();

}

}

Output

Strating Thread #1

Strating Thread#2

Thread #1

Thread #2

B: 1

B: 2

B: 3

B: 4

B: 5

Thread 2 preempts the execution of thread 1

-----End of Thread #2-------

A: 1

A: 2

A: 3

A: 4

A: 5

------End of Thread #1-------

Program explanation

In above program,

1) We have created two threads - the Thread#1 and Thread#2.

2) We assign highest priority to Thread#2.

3) In the main function both the threads are started but as the Thread #2 has higher priority than the Thread#1, the Thread #2 preempts the execution of Thread#1.

4) Thus Thread #2 completes its execution and then Thread #1 completes.