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This article mainly introduces "how to stop java threads". In daily operation, I believe many people have doubts about how to stop java threads. The editor consulted all kinds of materials and sorted out simple and easy-to-use operation methods. I hope it will be helpful to answer the doubts about "how to stop java threads". Next, please follow the editor to study!

Wrong thread abort-stop

First of all, let's explain a wrong way to abort a thread-stop: abort the thread and clear the monitor lock information, but it can cause thread safety problems, JDK is not recommended, and a similar method is destory, which is not covered here because JDK has never implemented this method.

Next, we will use a program to explain why stop causes thread safety problems.

First define a thread class StopThread:

Public class StopThread extends Thread {private int i = 0; private int j = 0; @ Override public void run () {synchronized (this) {/ / add synchronization locks to ensure thread safety + + I; try {/ / hibernate for 10 seconds to simulate time-consuming operation Thread.sleep (10000) } catch (InterruptedException e) {e.printStackTrace ();} + + j;}} / * * print I and j * / public void print () {System.out.println ("I =" + I + "j =" + j);}}

What this thread does is to increment the two variables I and j in the synchronous code block, but sleep for 10 seconds during this execution. If the thread is aborted with the stop method, it will result in incorrect I and j data. It can also be said that there is a thread safety problem in programming, because the main thread affects the incorrect data of the created StopThread thread. The ideal correct output should be either successful or failed, because the purpose of adding locks is to ensure that the operation is atomic or that these two variables are not disturbed by other threads during the operation.

Let's write the StopThreadDemo class to demonstrate an error using the stop method:

Public class StopThreadDemo {public static void main (String [] args) throws InterruptedException {StopThread thread = new StopThread (); thread.start (); / / hibernate for 1 second to ensure that the I variable increments successfully Thread.sleep (1000); / / pauses thread thread.stop () / / incorrect termination of while (thread.isAlive ()) {/ / ensure that the thread has terminated} / / output the result thread.print ();}}

In the StopThreadDemo class, the StopThread thread is created and started, which is to perform the self-increment operation of variables I and j, but this self-increment operation is a synchronous code block wrapped with the synchronization keyword, so that the self-increment operation of the two variables is atomic and will not be disturbed by other threads to ensure thread safety.

However, within 10 seconds of thread dormancy, if you abort the thread through the stop method, you will find that the output result is iSuppli 1 jig0, that is, the first half of the code I self-increment, but the self-increment failure of the second half j will make the data in the thread inconsistent, thus the atomic goal of synchronizing the code block has not been achieved, undermining thread safety.

Correct thread abort-interrupt

After introducing the wrong way to abort, let's learn the correct thread abort-interrupt:

If the target thread blocks when calling Object class's wait (), wait (long) or wait (long,int) methods, join (), join (long,int), or sleep (long,int) methods, interrupt takes effect, the thread's interrupted state is cleared, and an InterruptedException exception is thrown.

If the target thread is blocked by IO or Channel in NIO, the same IO operation will be interrupted to return a special outlier to achieve the purpose of aborting the thread.

If none of the above conditions are met, the interrupt state of this thread is set.

Next, change the stop in StopThreadDemo to interrupt to see what the running result is:

Java.lang.InterruptedException: sleep interrupted at java.lang.Thread.sleep (Native Method) at com.wupx.thread.StopThread.run (StopThread.java:18) iTunes 1 juni1

It can be found that the self-increment of the two variables can be executed normally, ensuring the data consistency of the execution. Interrupt will not be forced to abort and interrupt the thread directly, but will notify us when an exception is thrown, and the developer can control the execution logic after receiving the exception, leaving the whole program in a thread-safe state. This is the interrupt method recommended in the current JDK version.

In addition to the correct method of interrupt, you can abort a thread in the form of flag bits:

Correct thread abort-flag bit if the code program logic is a circular execution business, you can add a flag bit to the thread code during the execution of the program, such as the following code to execute the program in the while loop, to control whether the program continues to execute through flag, and if the flag is changed to false in an external thread, the change in this data will be received in the created child thread code Through the form of this variable, notify to another thread, so as to achieve the effect of controlling thread abort.

Java.lang.InterruptedException: sleep interrupted at java.lang.Thread.sleep (Native Method) at com.wupx.thread.StopThread.run (StopThread.java:18) iTunes 1 juni1

By running the code, the results are as follows:

The running program is finished.

This approach is limited by the business logic executed in the thread, and it can be done in this way if there are conditions in the program that can be used as flag bits, and it is also a correct way to abort the thread.

At this point, the study on "how to abort the java thread" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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