Thread Life Cycle

 

Thread life cycle

Thread goes through various stages in its lifecycle.

for example in laymen terminologies we are creating the thread, starting the thread, running the threads, waiting the thread, terminating the thread.

 

A thread can be in one of the five states

1) New State

2) Runnable State

3) Running State

4) Non-Runnable State

5) Terminated

 

1) New State:

A new thread begins its life cycle in the new state, in this state a thread has been created, but it has not yet started.

A thread is started by calling it’s start() method.

 

Note: start() method is executing its referenced object run() method.

run() method available inside thread class and runnable interface.

If we want to create a new thread we should override run() method by extending Thread class/implementing Runnable Interface.

 

2) Runnable State:

This state is also called ready to run state, also called queue.

A thread starts life in the ready to run state by calling start() method and wait for its turn.

The Thread scheduler decides which thread runs and for how long.

 

Note: thread scheduler in Java is part of JVM that decides which thread should run and which thread should wait there are number of factor or criteria which are used to select a thread.

The thread scheduler always chooses a thread to run only if it is in the runnable state.

 

3) Running State:

The Running state doesn’t exist in reality but its consider as a part of runnable state.

In runnable state the control transfer to the thread scheduler and thread scheduler picks one of the threads from the Runnable thread pool and change its state to Running.

If a thread is in running state, it means that the thread is currently executing.

 

4) Non-Runnable State:

When a thread is in the Blocked state it is not eligible to run. Although the thread is considered to be alive.

A Runnable thread can move to the Blocked state if a thread wants to perform some operation but can’t complete immediately so it must temporarily wait until that task completes.

After the Blocked state, the thread moves to the Runnable state and waiting for the CPU cycle.

 

5) Terminated:

It is the state of a dead thread, it’s in the terminated state. When it has either finished execution or was terminated abnormally.

A thread after exit from the run() method will be in terminated state, or we can stop the thread forcefully using stop() method.

 

 

 

Inter Thread Communication

The wait() method is used for interthread communication.

The wait() method is defined in Object class which is the super most class in Java.

In Java synchronized methods and blocks allow only one thread to acquire the lock on a resource at a time.

So wait() method called by a thread, than it gives up the lock on that resource and goes to sleep until  some other thread enters the same monitor and calls notify() or notifyAll().

It is a final method, so we can’t override it.

Example Program:

Output