Life Cycle of a Thread

Definition

The life cycle of a thread in Java represents the various states a thread transitions through from its creation until it completes its execution or is terminated by the Java Virtual Machine (JVM).

Main Content

1. New State

• A thread is in the "New" state when an instance of the Thread class is created using the new keyword, but the start() method has not yet been invoked.
• At this stage, the thread is just an object in the heap memory; no resources are allocated for execution.

2. Runnable State

• Once the start() method is called, the thread moves to the "Runnable" state.
• In this state, the thread is ready to run and is waiting for the thread scheduler to allocate CPU time slice.

3. Running State

• This occurs when the thread scheduler selects the thread from the runnable pool to execute its run() method.
• The thread actively executes the instructions defined within its task logic.

Working / Process

1. Waiting / Blocked / Sleeping

• A thread enters the "Blocked" state when it is waiting for a monitor lock to enter a synchronized block or method.
• It enters "Waiting" or "Timed Waiting" when it calls methods like wait(), sleep(), or join(), pausing its execution until a specific condition is met or time elapses.

2. Execution Flow

• The CPU manages the context switching between multiple threads.
• The thread transitions back to "Runnable" once the waiting condition is satisfied or the sleep time expires.

3. Terminated (Dead)

• A thread enters the "Terminated" state when its run() method completes naturally or due to an unhandled exception.
• Once dead, a thread cannot be restarted.

       [New]
         |
      start()
         v
    [Runnable] <---> [Running]
         |             |
  (Wait/Sleep/Block) <---
         |
    [Terminated]

Advantages / Applications

• Improved Responsiveness: Allows applications to handle user input while performing heavy background tasks.
• Resource Optimization: Enables efficient utilization of multi-core processors by executing tasks in parallel.
• Task Decoupling: Facilitates the design of complex systems where different modules run independently without blocking one another.

Summary

The life cycle of a Java thread describes the states—New, Runnable, Running, Blocked, and Terminated—that a thread moves through during its existence. By managing these transitions, Java ensures efficient multitasking and concurrency in software development.

• New: Thread object created.
• Runnable: Ready for execution.
• Running: Currently executing code.
• Blocked/Waiting: Paused for resources or time.
• Terminated: Execution finished.
• Important Terms: Thread Scheduler, Context Switching, Monitor Lock, Runnable Interface.