thread life cycle in java
Understanding the Life Cycle of Threads in Java
thread life cycle in java
In Java, the thread life cycle consists of several states that a thread goes through during its execution. Initially, a thread is in the New state when it is created but not yet started. Once the `start()` method is invoked, it moves to the Runnable state, where it is eligible for running but may not be actively executing, as it competes for CPU time with other threads. When a thread is executing, it is in the Running state. A thread can transition to the Blocked state when it is waiting for a monitor lock to enter a synchronized block or method. If it's waiting for another thread to perform a particular action, it enters the Waiting state, and it can also move to the Timed Waiting state if it waits for a specified time. Once a thread finishes its execution, it enters the Terminated state, signaling that the thread has completed its task or has been terminated due to an exception. This life cycle is managed by the Java Virtual Machine (JVM) and the underlying operating system.
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1 - New/Created State: When a thread is instantiated using the `Thread` class (or implementing the `Runnable` interface), it enters the New state. In this state, the thread is not yet alive and has not started executing.
2) Runnable State: After the `start()` method is called on a thread, it transitions to the Runnable state. A thread in this state is eligible for running but not necessarily executing. The thread scheduler determines whether the thread is executing.
3) Blocked State: A thread can enter the Blocked state when it is trying to access a synchronized block or method that is currently being held by another thread. In this state, the thread cannot proceed until the lock is released.
4) Waiting State: A thread enters the Waiting state when it calls methods such as `wait()`, `join()`, or `LockSupport.park()`. In this state, the thread is waiting for another thread to perform a particular action, such as notifying it or completing execution.
5) Timed Waiting State: Similar to the Waiting state, a thread can enter the Timed Waiting state if it calls methods like `sleep(milliseconds)`, `wait(milliseconds)`, or `join(milliseconds)`. The thread will remain in this state for a specified time or until it is notified.
6) Terminated State: A thread enters the Terminated state when it has completed execution either normally (reached the end of the `run()` method) or abnormally (due to an unhandled exception). In this state, the thread cannot be started again.
7) Thread Scheduler: The Thread Scheduler is the component of the Java Virtual Machine (JVM) that manages the threads' execution. It determines which thread to run and for how long, typically based on priorities and the current state of threads.
8) Thread Priorities: Threads can be assigned different priorities using the `setPriority(int priority)` method. The scheduler uses these priorities to decide the order in which threads are executed, but it's not guaranteed; it is up to the implementation of the JVM and the underlying operating system.
9) Concurrency: The lifecycle of threads enables concurrency in Java applications. By allowing multiple threads to execute simultaneously, programs can efficiently use system resources and improve performance, especially in tasks like I/O operations, network calls, or parallel processing.
10) Synchronization: To avoid unexpected behavior due to concurrent accesses, Java provides synchronized methods and blocks. Proper synchronization ensures that shared resources are accessed by only one thread at a time, preventing data inconsistency.
11) Thread Safety: Thread life cycle management is essential for ensuring thread safety. Utilizing proper techniques such as synchronization, atomic variables, or concurrency utilities like `java.util.concurrent`, developers can create robust applications.
12) Daemon Threads: A daemon thread is a low priority thread that does not prevent the JVM from exiting when the program finishes. Daemon threads are used for background tasks, like garbage collection, and can be set using `setDaemon(true)`.
13) Thread Interruption: A thread can be interrupted using the `interrupt()` method. This raises the interrupted status of the thread and can be used to control thread execution, especially when waiting or sleeping.
14) Thread State Transitions: Understanding transitions between different states (New > Runnable, Runnable > Blocked, Blocked > Runnable, Waiting > Runnable, Timed Waiting > Runnable, and Running > Terminated) is crucial for managing threads effectively.
15) Best Practices: Familiarizing students with best practices for thread management, such as minimizing thread creation, using thread pools, avoiding deadlocks, and understanding the importance of clean resource handling, will make them better programmers.
This structured approach outlines the comprehensive thread life cycle in Java and can help students understand how threading works, the various states a thread can be in, and how to manage threads effectively.
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