Lifecycle and States of a Thread in Java

In Java programming, threads enable concurrent execution and multitasking within an application. Understanding the life cycle of threads in Java and the various states is essential for efficient and synchronized thread management.

The life cycle of Thread in Java refers to the various stages a thread goes through during its execution. A thread can exist in different states throughout its life cycle, each with specific characteristics and behaviors. In this article, we will explore the thread life cycle in Java and its states in Java. 

Threads in Java

Before we discuss thread life cycle in Java, let’s threads in java. The term Threads in Java is a lightweight process that allows multiple tasks to be executed simultaneously within a single program. It enables the application to perform two or more actions concurrently, thus improving the system's performance. Threads can exist in various states like ready, running, waiting and dead during their lifecycle, and each state has different characteristics. They are also known as lightweight processes because they share common memory and resources with other threads within the process. Threads are an essential part of the Java programming language as they can be used to achieve parallelism and improve performance and responsiveness. In short, Threads are a vital part of multithreaded programming in Java.

An Accelerator Program in Business Analytics and Data Science can help you gain the skills necessary to succeed as a Data Scientist. Java is a commonly used programming language in Data Science and Business Analytics. Therefore, understanding the lifecycle and states of a thread in Java is essential for professional success.

Importance of understanding the life cycle of Thread in Java and its states

The thread life cycle in Java is an important concept in multithreaded applications. Let’s see the importance of understanding life cycle of thread in java: 

1. Understanding the life cycle of a thread in Java and the states of a thread is essential because it helps identify potential issues that can arise when creating or manipulating threads.
2. It allows developers to utilize resources more effectively and prevent errors related to multiple threads accessing shared data simultaneously.
3. Knowing the thread states in Java helps predict a program's behaviour and debug any issues that may arise.
4. It also guides the developer on properly suspending, resuming, and stopping a thread as required for a specific task.

The Life Cycle of Thread in Java - Threads State 

In Java, the life cycle of Thread goes through various states. These states represent different stages of execution. Here are examples of each stage of the life cycle of Thread in Java with real-life use cases:

• New (born) state

  • Example: Creating a new thread using the Thread class constructor.
  • Use case: Creating a new thread to perform a background task while the main Thread continues with other operations

• Runnable state

  • Example: After calling the start() method on a thread, it enters the runnable state.
  • Use case: Multiple threads competing for CPU time to perform their tasks concurrently.

• Running state

  • Example: When a thread executes its code inside the run() method.
  • Use case: A thread executing a complex computation or performing a time-consuming task.

• Blocked state:

  • Example: When a thread tries to access a synchronized block or method, but another thread already holds the lock.
  • Use case: Multiple threads accessing a shared resource can only be obtained by a single Thread, such as a database or a file.        

• Waiting state:

  • Example: Using the wait method inside a synchronized block, a thread can wait until another thread calls the notify() or notifyAll() methods to wake it up.
  • Use case: Implementing the producer-consumer pattern, where a thread waits for a specific condition to be met before continuing its execution

• Timed waiting state:

  • Example: Using methods like sleep(milliseconds) or join(milliseconds) causes a thread to enter the timed waiting state for the specified duration.
  • Use case: Adding delays between consecutive actions or waiting for the completion of other threads before proceeding.

• Terminated state:

  • Example: When the run() method finishes its execution or when the stop() method is called on the Thread.
  • Use case: Completing a task or explicitly stopping a thread's execution.

These examples demonstrate how threads can handle various scenarios in Java applications, allowing for concurrent and parallel execution of tasks. Understanding the different thread states helps in designing efficient and responsive multithreaded applications. Moreover, access modifiers in Java are also important to understand. Since these are used in multithreading programming, knowledge of them is important.

Thread Lifecycle Diagram (Visual representation)

The following diagram shows the complete life cycle of a thread.

Transitions Between Thread States

Threads in a multithreaded environment can transition between different thread states in Java as they execute. The Java Thread class defines these states and represents different stages in the lifecycle of a thread. The possible states include:

1. New: When a thread has just been created, it is in the "New" state. At this point, the Thread is not yet scheduled for execution and has not started running.
2. Runnable: A thread enters the "Runnable" state after invoking the start() method. In this state, the Thread is eligible to be scheduled by the operating system and can start executing its code.
3. Blocked/Waiting: A thread can enter the "Blocked" or "Waiting" state under certain circumstances. For example, if a thread is waiting for a lock to be released by another thread, it goes into the "Blocked" state. Similarly, if a thread waits for a specific condition to be satisfied, it enters the "Waiting" state. In these states, the Thread is not actively executing its code and is not eligible for scheduling.
4. Timed Waiting: Threads can also enter the "Timed Waiting" state, similar to the "Waiting" state but with a time constraint. For instance, a thread can enter the "Timed Waiting" state when it calls methods like Thread.sleep() or Object.wait() with a specific timeout value. The Thread remains in this specific state until the timeout expires or until it receives a notification from another thread.
5. Terminated: The final state in the thread lifecycle is the "Terminated" state. A thread enters this state when it completes its execution or when an unhandled exception occurs within the Thread. Once a thread is terminated, it cannot transition to any other state.

Example: Thread Life Cycle in Java:

Here's an example that demonstrates the life cycle of Thread in Java:

public class ThreadLifecycleExample {
    public static void main(String[] args) {
        Thread thread = new Thread(() -> {
            System.out.println("Thread is running.");
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println("Thread is terminating.");
        });
        System.out.println("Thread is in the New state.");
        thread.start();
        System.out.println("Thread is in the Runnable state.");
        
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("Thread is in the Timed Waiting state.");
        try {
            thread.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("Thread is in the Terminated");

Handling Thread Exceptions and Terminating Threads

When dealing with exceptions in life cycle of a thread java, there are several ways to handle them. 

• The most common way is wrapping the code in a try-catch block. 
• Moreover, when a thread is no longer needed, it should be terminated for the application to avoid memory leaks and other issues. To do this, invoke the Thread's interrupt() or stop() methods. The former method sends an interruption signal to the Thread, while the latter stops it immediately and can cause instability in some cases.

Best Practices and Tips for Thread Management

Certain best practices and tips can help keep the discussion organized and productive when managing threads.

1. Keep conversations on-topic: To ensure a thread is productive, make sure everyone stays on-topic and focused on the subject at hand. 
2. Monitor for trolling: Keep an eye out for trolls trying to derail the discussion. If someone is disruptive or offensive, address the issue promptly and don't hesitate to remove their posts if necessary.
3. Stay organized: Use threads and other organizational tools to keep track of the conversation. Assign a moderator if needed to ensure everything stays on track and everyone is heard.
4. Respond promptly: Make sure to respond promptly when someone has asked a question or raised an issue. This will help keep the discussion productive and ensure everyone gets their questions answered on time.

Considerations for Designing Multithreaded Applications

Designing multithreaded applications can be a complex process with many factors to consider such as: 

• Synchronization

  Thread synchronization is important when multiple threads access shared data to ensure that the data is consistent and accurate. Various techniques, such as locks, semaphores, monitors and atomic operations, can be used for thread synchronization.

• Memory Management

  Each Thread may require its own memory space, and multiple threads might need to access the same data from varied locations in memory. Careful management of memory is required to ensure that all threads can access the correct data at the right time.

• Multiple thread source Allocation

  Threads may also need to share resources such as processors, files or network connections. Resource allocation must be carefully managed to ensure that all threads get the resources they need when needed.

• Performance

  Multithreading in Java can benefit performance, as multiple threads can work concurrently on different tasks. Careful design of threading is required to ensure that the application makes effective use of system resources and achieves the desired problems

Conclusion

Understanding the states and lifecycle of threads in Java is essential for creating multithreaded applications. Knowing how to create a thread, pause, resume, or terminate it can help you develop efficient and reliable programs. With a fundamental understanding of these concepts, you can develop your multithreaded applications using Java.

Threads are a powerful tool but can also be difficult to debug if something were to go wrong. Hence, it is essential to test your code thoroughly before deployment and ensure that you know what all of the threads in your application are doing at any given time. With the right/correct knowledge and experience, working with threads can lead to a successful and efficient development process.