Thread Priorities
In Java, thread scheduler can use the thread priorities
in the form of integer value to each of its thread to
determine the execution schedule of threads . Thread gets the ready-to-run state
according to their priorities. The thread scheduler provides the CPU time to
thread of highest priority during ready-to-run state.
Priorities
are integer values from 1 (lowest priority given by the constant Thread.MIN_PRIORITY)
to 10 (highest priority given by the constant Thread.MAX_PRIORITY). The
default priority is 5(Thread.NORM_PRIORITY).
| Constant |
Description |
| Thread.MIN_PRIORITY |
The maximum
priority of any thread (an int value of 10) |
| Thread.MAX_PRIORITY
|
The minimum
priority of any thread (an int value of 1) |
| Thread.NORM_PRIORITY
|
The normal
priority of any thread (an int value of 5) |
The methods that are used to set the priority of thread shown as:
| Method |
Description |
setPriority()
|
This is method is used to set the priority of thread.
|
| getPriority()
|
This method is used to get the priority of thread.
|
When a Java thread is created, it inherits its priority
from the thread that created it. At any given time, when multiple threads
are ready to be executed, the runtime system chooses the runnable thread with
the highest priority for execution. In Java runtime system, preemptive
scheduling algorithm is applied. If at the execution time a thread with a
higher priority and all other threads are runnable then the runtime system
chooses the new higher priority thread for execution. On the other hand,
if two threads of the same priority are waiting to be executed by the CPU
then the round-robin algorithm is applied in which the scheduler chooses
one of them to run according to their round of time-slice.
Thread
Scheduler
In the implementation of threading
scheduler usually applies one of the two following strategies:
-
Preemptive scheduling – If the new thread
has a higher priority then current running thread leaves the runnable state and higher priority thread
enter to the runnable state.
-
Time-Sliced (Round-Robin) Scheduling –
A running thread is allowed to be execute for the fixed time, after completion
the time, current thread indicates to the another thread to enter it in the runnable state.
You can also set a thread's priority at any time after its
creation using the setPriority method. Lets see, how to set
and get the priority of a thread.
class MyThread1 extends Thread{
MyThread1(String s){
super(s);
start();
}
public void run(){
for(int i=0;i<3;i++){
Thread cur=Thread.currentThread();
cur.setPriority(Thread.MIN_PRIORITY);
int p=cur.getPriority();
System.out.println("Thread Name :"+Thread.currentThread().getName());
System.out.println("Thread Priority :"+cur);
}
}
}
class MyThread2 extends Thread{
MyThread2(String s){
super(s);
start();
}
public void run(){
for(int i=0;i<3;i++){
Thread cur=Thread.currentThread();
cur.setPriority(Thread.MAX_PRIORITY);
int p=cur.getPriority();
System.out.println("Thread Name :"+Thread.currentThread().getName());
System.out.println("Thread Priority :"+cur);
}
}
}
public class ThreadPriority{
public static void main(String args[]){
MyThread1 m1=new MyThread1("My Thread 1");
MyThread2 m2=new MyThread2("My Thread 2");
}
}
|
Output of the Program:
C:\nisha>javac ThreadPriority.java
C:\nisha>java ThreadPriority
Thread Name :My Thread 1
Thread Name :My Thread 2
Thread Priority :Thread[My Thread 2,10,main]
Thread Name :My Thread 2
Thread Priority :Thread[My Thread 2,10,main]
Thread Name :My Thread 2
Thread Priority :Thread[My Thread 2,10,main]
Thread Priority :Thread[My Thread 1,1,main]
Thread Name :My Thread 1
Thread Priority :Thread[My Thread 1,1,main]
Thread Name :My Thread 1
Thread Priority :Thread[My Thread 1,1,main] |
In this program two
threads are created. We have set up maximum priority for the first thread
"MyThread2" and minimum priority for the first thread
"MyThread1" i.e. the after executing the program, the
first thread is executed only once and the second thread "MyThread2"
started to run until either it gets end or another thread of the equal
priority gets ready to run state.
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this Program
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