Analyze several states of Java threads and their application scenarios

Analysis of several states of Java threads and their application scenarios

Introduction:
In Java multi-thread programming, understand the status of threads and the switching of different states is very important. Understanding thread status helps us better manage threads and improve program performance and reliability. This article will introduce several states of Java threads in detail, and combine specific code examples to illustrate the application scenarios of different states.

1. Several states of threads
Threads in Java have the following states:

1. New state (New): After the thread object is created, start has not been called yet () method, the thread is in the new state at this time.
2. Running state (Runnable): When the start() method is called, the thread enters the runnable state. At this time, it does not mean that the thread must be running, it just means that the thread has the conditions to run and is waiting for the system to schedule execution.
3. Blocked state (Blocked): The blocked state means that the thread is suspended due to the occurrence of certain conditions, and waits for the conditions to be met before continuing to run. For example, if a thread cannot continue execution because a synchronization block is locked, the thread will enter a blocking state.
4. Waiting state (Wait): Waiting state means that the thread enters the waiting queue and waits for the wake-up operation of other threads. When the thread executes the wait() method, the thread will release the lock it holds and enter the waiting state.
5. Timed_waiting state (Timed_waiting): Timed waiting state means that the thread automatically wakes up and enters the running state after waiting for a certain period of time. The thread can enter the timeout waiting state by calling the sleep() method or waiting for the I/O operation to complete.
6. Terminated state (Terminated): The thread enters the terminated state after completion of execution or abnormal termination.

2. Application scenarios of thread state

1. New state (New): In actual development, when we need to create a thread but have not yet called it When starting() method, the thread is in the new state. At this time, you can do some initialization operations for the thread, such as setting the name of the thread, etc.
   Sample code:

   Thread thread = new Thread(new Runnable(){
    @Override
    public void run() {
        // 线程执行的代码逻辑
    }
   }, "MyThread");

2. Running state (Runnable): When the start() method is called, the thread enters the running state and starts executing the code in the thread's run() method . At this time, the application scenario can be a task that needs to be executed concurrently by multiple threads, such as processing multiple client requests at the same time.
   Sample code:

   Thread thread = new Thread(new Runnable(){
    @Override
    public void run() {
        // 线程执行的代码逻辑
    }
   });
   thread.start();

3. Blocked state (Blocked): When a thread needs to access a locked synchronization block or resources occupied by other threads, the thread will enter the blocking state . At this time, the lock mechanism can be used to control the execution of the thread and ensure the correctness of the synchronization operation.
   Sample code:

   public class MyRunnable implements Runnable {
    private static Object lock = new Object();
   
    @Override
    public void run() {
        synchronized (lock) {
            // 执行同步操作
        }
    }
   }

4. Waiting state (Wait): When the thread executes the wait() method, the thread releases the lock resource and enters the waiting state, waiting for other threads to wake up. . The application scenario at this time is usually when multiple threads work together, and a thread needs to wait for notification from other threads before it can continue execution.
   Sample code:

   public class MyRunnable implements Runnable {
    private static Object lock = new Object();
   
    @Override
    public void run() {
        synchronized (lock) {
            try {
                lock.wait();
                // 线程被唤醒后执行的逻辑
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
   }

5. Timeout waiting state (Timed_waiting): Sometimes we need the thread to automatically wake up and continue execution after waiting for a period of time. In this case, you can use Thread.sleep( ) method or wait for the I/O operation to complete to put the thread into a timeout waiting state.
   Sample code:

   public class MyRunnable implements Runnable {
    @Override
    public void run() {
        try {
            Thread.sleep(5000); // 线程等待5秒后自动唤醒
            // 线程被唤醒后执行的逻辑
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
   }

6. Terminated state (Terminated): When the thread finishes executing the run() method, or the thread is terminated early due to exceptions or other reasons, the thread enters the terminated state. At this time, you can perform some cleanup work in the program, such as releasing resources, etc.
   Sample code:

   Thread thread = new Thread(new Runnable(){
    @Override
    public void run() {
        // 线程执行的代码逻辑
    }
   });
   thread.start();
   // 等待线程执行完成
   thread.join();
   // 线程已经终止，进行一些清理工作

Conclusion:
By learning and understanding the several states of Java threads and their application scenarios, we can better manage threads and improve the performance of the program performance and reliability. In actual development, rational use of various states of threads can make our multi-threaded programs more optimized and efficient.

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