Thread Priorities

[VelMurugan]

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.