Multi-thread safety issues in Java - solutions to java.lang.ThreadDeath

Java is a programming language widely used in modern software development, and its multi-threaded programming capability is also one of its greatest advantages. However, due to the concurrent access problems caused by multi-threading, multi-thread safety issues often occur in Java. Among them, java.lang.ThreadDeath is a typical multi-thread security issue. This article will introduce the causes and solutions of java.lang.ThreadDeath.

1. Reasons for java.lang.ThreadDeath

In Java, thread stopping is usually caused by two situations. One is that the thread completes execution and stops automatically; the other is that the thread stops automatically. was forced to stop. For the former situation, the Java virtual machine can handle it very well, but for the latter situation, java.lang.ThreadDeath exceptions are prone to occur.

ThreadDeath is a very special exception that can only be thrown by the Java virtual machine (sun.misc.InnocuousThread class). It occurs because when one thread tries to end another thread, some exceptions occur while the other thread is waiting, causing the execution of the thread to be interrupted. This kind of exception is used to coordinate cooperation between different threads. When a thread exception occurs, other threads will stop waiting and terminate their own execution. java.lang.ThreadDeath is thrown by the thread manager, and we usually should not throw it explicitly ourselves.

2. Solution to java.lang.ThreadDeath

Since java.lang.ThreadDeath is an exception automatically thrown by the Java virtual machine, the program cannot catch and handle the exception. Therefore, when programming with multiple threads, try to avoid using methods such as stop() in the thread that will forcefully terminate the thread, because this may cause a java.lang.ThreadDeath exception.

When you need to end the thread, you can set a flag to let the thread stop automatically. For example:

public class MyThread extends Thread {

    private boolean flag = true;

    public void stopThread() {
        flag = false;
    }

    @Override
    public void run() {
        while (flag) {
            // do something
        }
    }
}

In the above example, the MyThread thread has a flag flag, and the while loop in the run() method will determine whether to continue execution based on the value of the flag bit. When you need to end the MyThread thread, you can call the stopThread() method to modify the flag bit so that the thread stops automatically. This can avoid using the stop() method of the Java virtual machine in the program and avoid java.lang.ThreadDeath exceptions.

Another way is to use the Thread.interrupt() method, which is a better way to forcefully abort (or stop) the thread. When we need to end a thread, we can use the Thread.interrupt() method, which sends a thread interrupt signal to the target thread and notifies the target thread to stop execution. When the target thread receives an interrupt signal, it can choose to continue execution or return immediately.

In your multi-threaded application, suppose there is a thread waiting for some event and executing some external service. At this time, you apply to exit the program, but if you want the thread to execute until the service is completed before exiting, you can send an interrupt signal to the thread:

Thread serviceThread = new Thread(new YourLongRunningIntervalClass());
serviceThread.start();

// 程序即将结束
serviceThread.interrupt();

In the above example, when the interrupt() method is run, An interrupt signal will be sent to serviceThread. If the thread is waiting for an event and does not actively check the interrupt status, the thread will continue to wait; if the thread checks the interrupt status, it can choose to return immediately.

3. Summary

Multi-threaded programming is a major advantage of Java, but multi-thread safety also needs to be paid attention to. By avoiding the use of the stop() method provided by the Java virtual machine and rational use of the Thread.interrupt() method, we can effectively avoid java.lang.ThreadDeath exceptions and make our programs more robust and efficient.

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