Explore Java thread state and its importance in concurrent programming

Explore several states of Java threads and their role in concurrent programming

In Java, threads are the basic unit of multitasking and have the capability of concurrent execution. ability. Threads can have different states, which are represented by state constants in Java's Thread class. Knowing and understanding the various states of threads is critical to writing reliable concurrent programs. This article will explore several states of Java threads and their role in concurrent programming, and illustrate them through specific code examples.

1. New state (NEW)

When a thread instance is created, it is in the new state. At this point, the thread instance has been created but not started yet. New threads can be created by creating an instance of the Thread class.

The sample code is as follows:

Thread thread = new Thread();

2. Runtable state (RUNNABLE)

In the runnable state, the thread has been started and is executing, and Probably waiting for available CPU resources. The runnable state is a state in which a thread is running in the context of a process and has the ability to start immediately.

The sample code is as follows:

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

3. Blocked state (BLOCKED)

When a thread is waiting to acquire the lock resource of an object, it is considered It is a blocking state. Threads can acquire locks through the synchronized keyword. When a thread acquires the lock resource of an object, other threads are blocked and must wait for the thread that acquired the lock to release the lock resource before they can continue execution.

The sample code is as follows:

public class MyRunnable implements Runnable {
    private final Object lock = new Object();

    public void run() {
        synchronized (lock) {
            // 获取锁资源
            // 执行需要同步的代码
        }
    }
}

4. Waiting state (WAITING)

When a thread waits for a specified condition, it is considered to be in the waiting state . A thread can enter the waiting state by calling the wait() method of the Object class or the sleep() method of the thread. The thread in the waiting state will release the lock resource it holds.

The sample code is as follows:

final Object lock = new Object();

Thread thread1 = new Thread(new Runnable() {
    public void run() {
        synchronized (lock) {
            try {
                lock.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
});

5. Timeout waiting state (TIMED_WAITING)

When a thread waits for a specified period of time, it is considered Timeout waiting state. A thread can enter the timeout waiting state by calling the sleep() method of Thread or the wait(long timeout) method of the Object class. The thread in the timeout waiting state will release the lock resources it holds.

The sample code is as follows:

Thread thread1 = new Thread(new Runnable() {
    public void run() {
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
});

6. Termination status (TERMINATED)

When the thread finishes executing its run() method or an exception occurs, it is considered a terminal state. Threads in the terminated state are no longer executed.

The sample code is as follows:

Thread thread1 = new Thread(new Runnable() {
    public void run() {
        // 线程执行的代码
    }
});
thread1.start();
// 等待线程执行完毕
try {
    thread1.join();
} catch (InterruptedException e) {
    e.printStackTrace();
}

Understanding the various states of threads is basic knowledge in concurrent programming, and they play a key role in the correct writing and debugging of multi-threaded applications. Through the above sample code, we can better understand and master the concept of Java thread state, and be able to write more reliable and efficient concurrent programs.

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