In Java, a thread executes when it gets its CPU time, and when a thread gets CPU time, it depends on the current CPU scheduling algorithm.
When a thread is created, JVM assigns a number to the thread, which is called the priority of the thread. In a Priority-Based Scheduling algorithm, the thread with the highest priority gets CPU time first.
There are three different types of Thread Priority:
1. MIN_PRIORITY: Minimum priority of the thread will be 1.
2. MAX_PRIORITY: Maximum priority of the Thread will be 10.
3. NORM_PRIORITY: Normal priority of the Thread will be 5.
When we create a thread, JVM internally assigns a default priority, which is normal priority with a value of 5. However, using the setPriority(int) and getPriority() methods of the java.lang.Thread class, we can set or get the priority of the thread, respectively.
Access Modifier: - public
Return Type: - void
Method Name: - setPriority
Parameter: - int
Functionality: - As we can see, the setPriority() method is an instance method that takes an int type parameter. When we invoke the setPriority() method of a thread class object and pass an int type argument, that argument is assigned to the current thread as its priority. The thread priority must be set in the range of 1 to 10. If we attempt to assign an illegal priority, we will encounter an IllegalArgumentException at runtime.
Access Modifier: - public
Return Type: - int
Method Name: - getPriority
Functionality: - When we invoke getPriority() method then it return the priority of the current thread.
class JTC{
public static void main(String arg[]){
Thread t1 = new Thread();
System.out.println("default-priority :- "+t1.getPriority());
t1.setPriority(10);
System.out.println("thread-priority :- "+t1.getPriority());
t1.setPriority(1);
System.out.println("thread-priority :- "+t1.getPriority());
t1.setPriority(0);
}
}
default-priority :- 5
thread-priority :- 10
thread-priority :- 1
Exception in thread "main" java.lang.IllegalArgumentException
at java.lang.Thread.setPriority(Thread.java:1089)
at JTC.main(test.java:9)
Note:- There is no use of Thread Priority when CPU scheduling algorithm is not Priority based algorithm.
Ques:-What happens when the current working CPU scheduling algorithm is a priority-based algorithm and more than one thread has the same priority
In that case, when more than one thread falls under the priority-based scheduling algorithm and has the same priority, the system may attempt to switch to another scheduling algorithm. Based on that, it can select a specific thread. We cannot predict which scheduling algorithm will be adopted by the CPU scheduler.