I met the problem of concurrent programming in an interview: how to safely interrupt a running thread

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One bit 5 In, my little friend went to a certain East for an interview and was given a concurrent programming interview question Pass 了 , say ” How to interrupt a running thread ？, A lot of work has been done on this issue 2 We all know , It's a pity .

today , Let me share with you my answer .

1、 What is thread ？

Before I answer that question , Let's review what threads ？

Thread, Thread is the smallest unit of operation scheduling . therefore , Thread is a system level concept .

And in the Java The thread implemented inside , The final execution and scheduling are determined by the operating system ,JVM It's just a layer of packaging for threads at the operating system level .

So we are Java It calls start() Method starts a thread , Just tell the operating system that this thread can be executed , But finally to CPU To execute , It is determined by the scheduling algorithm of the operating system .

2、 How to operate how to safely interrupt a running thread ?

In theory , To be in Java Level to interrupt a running thread , Only like Linux Inside kill The command ends the process in the same way , Mandatory termination .

Java Thread Of API Although it provides a stop() Method , Threads can be forcibly terminated , But this way is not safe , Because it is possible that the task of the thread has not been completed , Sudden interruptions can lead to incorrect results .

To safely interrupt a running thread , Only one hook can be buried inside the thread , External procedures Use this hook to trigger the interrupt command of the thread .

therefore , stay Java Thread There is a interrupt() Method , This method should cooperate with isInterrupted() Method to use , You can safely interrupt the thread .

Look at this code ：

Runnable runnable = new Runnable(){
    public void run() {
        while (true) {
            if (Thread.currentThread().isInterrupted()){
                System.out.println(" The thread was interrupted ");
                return ;
            } else {
                System.out.println(" The thread is not interrupted ");
            }
        }
    }
};
Thread t = new Thread(runnable);
t.start();
Thread.sleep(500);
t.interrupt();
System.out.println(" Thread interrupted , Here's the program ");

This implementation is not a forced interrupt , Instead, it tells the running thread , You can stop . When to actually interrupt , Depends on the running thread , therefore , It can ensure the security of the running results of threads .

This problem , A lot of work 5 Little friends over years don't necessarily know . although CRUD Proficient , however , It is often outside of work that others are left behind 8 Hours .

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