life cycle of multithreading in java
Understanding the Lifecycle of Multithreading in Java
life cycle of multithreading in java
In Java, the life cycle of a thread is governed by various states that a thread can be in during its execution. A thread starts in the New state when it is created using the `Thread` class or by implementing the `Runnable` interface. It transitions to the Runnable state when the `start()` method is called, at which point it is ready to run but may not be actively executing due to scheduling. A thread can enter the Blocked state when it is waiting for a monitor lock (e.g., when another thread is holding a lock that it needs). It may also enter the Waiting state when it is waiting for another thread to perform a particular action (like calling `wait()` or `join()`). After completing its execution, the thread moves to the Terminated state, indicating that it has finished running or has been terminated due to an exception. Throughout its life cycle, thread scheduling and management are handled by the Java Virtual Machine (JVM) and the underlying operating system, which coordinate execution based on various factors like priority and system load.
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1 - New State (Born State):
When a thread is created using the `Thread` class or implementing the `Runnable` interface, it is in the new state. It is not yet started and all its properties are initialized.
2) Runnable State:
A thread enters the runnable state after the `start()` method is invoked. In this state, the thread is ready to run and waiting for CPU time. It can be in the runnable state even while waiting for scheduling by the JVM.
3) Blocked State:
A thread enters the blocked state when it tries to access a monitor lock that is held by another thread. It will stay in this state until the lock is released.
4) Waiting State:
A thread enters the waiting state when it calls methods like `wait()`, `join()`, or `LockSupport.park()`. In this state, the thread is waiting for another thread to perform a particular action or signal.
5) Timed Waiting State:
Similar to the waiting state, but a thread enters the timed waiting state when it calls methods like `sleep(milliseconds)`, `wait(milliseconds)`, or `join(milliseconds)`. It will exit this state either when it is notified or the specified time has elapsed.
6) Terminated State (Dead State):
A thread enters the terminated state once it completes its execution naturally (returns from `run()`) or it is forcibly terminated due to an uncaught exception. In this state, the thread cannot be started again.
7) Thread Priorities:
Every thread in Java has a priority which indicates the relative importance of threads. It helps the operating system to decide which thread to run when there are multiple runnable threads. The range of priorities is between 1 (lowest) and 10 (highest).
8) Thread Scheduling:
The Java Virtual Machine (JVM) uses the thread scheduler to allocate CPU time to threads. The scheduling can be preemptive or time sliced, and multiple algorithms can be used based on the operating system.
9) Synchronization:
Thread synchronization is a critical concept in multithreading. It is used to prevent thread interference and memory consistency errors when multiple threads access shared resources. Java uses synchronized blocks and methods for this purpose.
10) Volatile Variables:
Declaring a variable as `volatile` ensures that changes to that variable are immediately visible to all threads. It's a lighter option than synchronization but only works for specific cases where a single variable is accessed.
11) Thread Communication:
Threads can communicate with each other using `wait()`, `notify()`, and `notifyAll()` methods, which are part of the Object class. This is useful for coordinating actions among threads.
12) Daemon Threads:
A daemon thread is a thread that runs in the background and does not prevent the JVM from exiting when the program finishes. You can create a daemon thread by calling `setDaemon(true)` on a thread instance.
13) Thread Groups:
Threads can be organized into groups. Java provides the `ThreadGroup` class which allows managing a group of threads collectively, useful for controlling their behavior (like interrupting all threads in a group).
14) Thread Pools:
Java has the Executors framework that simplifies multithreading and helps in managing a pool of threads efficiently. Thread pools reduce the overhead of thread creation and destruction.
15) Handling Exceptions:
Each thread has its own exception handling. You can catch exceptions thrown by a thread in the `run()` method, and also use `UncaughtExceptionHandler` to handle uncaught exceptions in a controlled manner.
16) Thread States Summary:
The overall management of thread states in Java follows a cycle: New → Runnable → Running → Blocked/Waiting/Timed Waiting → Terminated. Understanding these states helps in debugging and optimizing multithreaded applications.
Conclusion:
Understanding the lifecycle of threads in Java is fundamental for building efficient and effective multithreaded applications. Knowledge of thread states, synchronization, and communication methods will empower you to manage concurrent programming challenges effectively.
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