Life Cycle of a Thread

The life cycle of a thread in a programming context, including Java, refers to the various states a thread goes through during its execution. These states are managed by the operating system and the Java Virtual Machine (JVM). In Java, the Thread class provides methods to interact with and manage threads. Here are the different states in a thread’s life cycle:

1. New: A thread is in this state when an instance of the Thread class has been created, but the start() method has not been called on it. In this state, the thread has not yet started executing.
2. Runnable: Once the start() method is called on a thread instance, it enters the runnable state. In this state, the thread is ready to run but might not be currently executing due to other threads also being in the runnable state. The actual execution timing is managed by the operating system’s thread scheduler.
3. Running: In this state, the thread is actively executing its code. It transitions from the runnable state to the running state when the thread scheduler selects it to run. The run() method of the thread’s Runnable target is being executed.
4. Blocked (Waiting): A thread can enter this state for various reasons, such as waiting for a resource, waiting for I/O, or waiting for a notification from another thread. In this state, the thread is not executing and is blocked until the condition it’s waiting for is satisfied.
5. Timed Waiting: Similar to the blocked state, a thread can enter this state when it’s waiting for a specific amount of time. It will stay in this state until either the time elapses or the condition it’s waiting for is satisfied.
6. Terminated (Dead): A thread enters this state when its run() method has finished executing or when an unhandled exception occurs within the thread. Once in the terminated state, the thread cannot transition to any other state. Once a thread is terminated, it cannot be restarted.

Here’s a visual representation of the thread life cycle:

New -> Runnable -> Running -> (Blocked/Timed Waiting) -> Runnable -> Running -> Terminated

It’s important to note that the transitions between these states are managed by the JVM and the operating system’s thread scheduler. Also, threads can be paused, resumed, or stopped using methods provided by the Thread class, such as suspend(), resume(), and stop(). However, these methods are generally considered unsafe and are not recommended for modern thread management due to potential concurrency issues and resource leaks. It’s better to use higher-level synchronization and concurrency mechanisms provided by the Java standard library for more controlled thread management.