How do you kill a Thread in Java

Question

How do you kill a java lang Thread in Java

User · Answer

There is a way how you can do it  But if you had to use it  either you are a bad programmer or you are using a code written by bad programmers  So  you should think about stopping being a bad programmer or stopping using this bad code  This solution is only for situations when THERE IS NO OTHER WAY   Thread f    lt A thread to be stopped gt  Method m   Thread class getDeclaredMethod   stop0    new Class   Object class     m setAccessible  true    m invoke  f   new ThreadDeath

User · Answer

There is of course the case where you are running some kind of not-completely-trusted code   I personally have this by allowing uploaded scripts to execute in my Java environment  Yes  there are security alarm bell ringing everywhere  but it s part of the application   In this unfortunate instance you first of all are merely being hopeful by asking script writers to respect some kind of boolean run don t-run signal  Your only decent fail safe is to call the stop method on the thread if  say  it runs longer than some timeout   But  this is just  decent   and not absolute  because the code could catch the ThreadDeath error  or whatever exception you explicitly throw   and not rethrow it like a gentlemanly thread is supposed to do  So  the bottom line is AFAIA there is no absolute fail safe

User · Answer

One way is by setting a class variable and using it as a sentinel   Class Outer       public static volatile flag   true       Outer             new Test   start              class Test extends Thread            public void run                 while  Outer flag                      do stuff here                                    Set an external class variable  i e  flag   true in the above example  Set it to false to  kill  the thread

User · Answer

Killing a thread  is not the right phrase to use  Here is one way we can implement graceful completion exit of the thread on will   Runnable which I used   class TaskThread implements Runnable        boolean shouldStop       public TaskThread boolean shouldStop            this shouldStop   shouldStop              Override     public void run              System out println  Thread has started             while   shouldStop                   do something                    System out println  Thread has ended                public void stop             shouldStop   true             The triggering class   public class ThreadStop        public static void main String   args             System out println  Start                Start the thread         TaskThread task   new TaskThread false           Thread t   new Thread task           t start                Stop the thread         task stop             System out println  End

User · Answer

Here are a couple of good reads on the subject   What Do You Do With InterruptedException   Shutting down threads cleanly

User · Answer

Attempts of abrupt thread termination are well-known bad programming practice and evidence of poor application design  All threads in the multithreaded application explicitly and implicitly share the same process state and forced to cooperate with each other to keep it consistent  otherwise your application will be prone to the bugs which will be really hard to diagnose  So  it is a responsibility of developer to provide an assurance of such consistency via careful and clear application design   There are two main right solutions for the controlled threads terminations    Use of the shared volatile flag Use of the pair of Thread interrupt   and Thread interrupted   methods    Good and detailed explanation of the issues related to the abrupt threads termination as well as examples of wrong and right solutions for the controlled threads termination can be found here   https   www securecoding cert org confluence display java THI05-J  Do not use Thread stop 28 29 to terminate threads

User · Answer

Generally you don t    You ask it to interrupt whatever it is doing using Thread interrupt    javadoc link   A good explanation of why is in the javadoc here   java technote link

User · Answer

Generally you don t kill  stop  or interrupt a thread  or check wheter it is interrupted     but let it terminate naturally   It is simple  You can use any loop together with  volatile  boolean variable inside run   method to control thread s activity  You can also return from active thread to the main thread to stop it   This way you gracefully kill a thread

User · Answer

In Java threads are not killed  but the stopping of a thread is done in a cooperative way  The thread is asked to terminate and the thread can then shutdown gracefully   Often a volatile boolean field is used which the thread periodically checks and terminates when it is set to the corresponding value   I would not use a boolean to check whether the thread should terminate  If you use volatile as a field modifier  this will work reliable  but if your code becomes more complex  for instead uses other blocking methods inside the while loop  it might happen  that your code will not terminate at all or at least takes longer as you might want      Certain blocking library methods support interruption    Every thread has already a boolean flag interrupted status and you should make use of it  It can be implemented like this   public void run        try         while   interrupted                                   catch  InterruptedException consumed           Allow thread to exit            public void cancel     interrupt        Source code adapted from Java Concurrency in Practice  Since the cancel   method is public you can let another thread invoke this method as you wanted

User · Answer

The question is rather vague  If you meant    how do I write a program so that a thread stops running when I want it to     then various other responses should be helpful  But if you meant    I have an emergency with a server I cannot restart right now and I just need a particular thread to die  come what may     then you need an intervention tool to match monitoring tools like jstack   For this purpose I created jkillthread  See its instructions for usage

User · Answer

There is no way to gracefully kill a thread   You can try to interrupt the thread  one commons strategy is to use a poison pill to message the thread to stop itself  public class CancelSupport       public static class CommandExecutor implements Runnable               private BlockingQueue lt String gt  queue              public static final String POISON PILL       stopnow                 public CommandExecutor BlockingQueue lt String gt  queue                        this queue queue                             Override             public void run                         boolean stop false                      while  stop                                try                                       String command queue take                                        if POISON PILL equals command                                                 stop true                                        else                                                  do command                                             System out println command                                                                       catch  InterruptedException e                                        stop true                                                                          System out println    Stopping execution                                BlockingQueue lt String gt  queue new LinkedBlockingQueue lt String gt     Thread t new Thread new CommandExecutor queue    queue put    hello      queue put    world      t start    Thread sleep 1000   queue put    stopnow        http   anandsekar github io cancel-support-for-threads

User · Answer

I d vote for Thread stop     As for instance you have a long lasting operation  like a network request   Supposedly you are waiting for a response  but it can take time and the user navigated to other UI  This waiting thread is now a  useless b  potential problem because when he will get result  it s completely useless and he will trigger callbacks that can lead to number of errors   All of that and he can do response processing that could be CPU intense  And you  as a developer  cannot even stop it  because you can t throw if  Thread currentThread   isInterrupted    lines in all code   So the inability to forcefully stop a thread it weird

User · Answer

I didn t get the interrupt to work in Android  so I used this method  works perfectly   boolean shouldCheckUpdates   true   private void startupCheckForUpdatesEveryFewSeconds         Thread t   new Thread new CheckUpdates         t start       private class CheckUpdates implements Runnable      public void run             while  shouldCheckUpdates                 Thread sleep 3 seconds             System out println  Do your thing here                        public void stop            shouldCheckUpdates   false

User · Answer

See this thread by Sun on why they deprecated Thread stop     It goes into detail about why this was a bad method and what should be done to safely stop threads in general     The way they recommend is to use a shared variable as a flag which asks the background thread to stop   This variable can then be set by a different object requesting the thread terminate

User · Answer

Thread stop is deprecated so how do we stop a thread in java    Always use interrupt method and future to request cancellation       When the task responds to interrupt signal  for example  blocking queue take method    Callable  lt  String  gt  callable   new Callable  lt  String  gt            Override     public String call   throws Exception           String result               try                 assume below take method is blocked as no work is produced              result   queue take              catch  InterruptedException e                Thread currentThread   interrupt                      return result           Future future   executor submit callable   try       String result   future get 5  TimeUnit SECONDS     catch  TimeoutException e        logger error  Thread timedout         return       finally         this will call interrupt on queue which will abort the operation        if it completes before time out  it has no side effects     future cancel true         When the task does not respond to interrupt signal Suppose the task performs socket I O which does not respond to interrupt signal and thus using above approach will not abort the task  future would time out but the cancel in finally block will have no effect  thread will keep on listening to socket  We can close the socket or call close method on connection if implemented by pool    public interface CustomCallable  lt  T  gt  extends Callable  lt  T  gt        void cancel        RunnableFuture  lt  T  gt  newTask       public class CustomExecutorPool extends ThreadPoolExecutor       protected  lt  T  gt  RunnableFuture  lt  T  gt  newTaskFor Callable  lt  T  gt  callable            if  callable instanceof CancellableTask              return   CancellableTask  lt  T  gt    callable  newTask            else             return super newTaskFor callable            public abstract class UnblockingIOTask  lt  T  gt  implements CustomCallable  lt  T  gt        public synchronized void cancel             try               obj close              catch  IOException e                logger error  io exception   e                        public RunnableFuture  lt  T  gt  newTask             return new FutureTask  lt  T  gt   this                public boolean cancel boolean mayInterruptIfRunning                    try                       this cancel                      finally                       return super cancel mayInterruptIfRunning

User · Answer

I want to add several observations  based on the comments that have accumulated    Thread stop   will stop a thread if the security manager allows it  Thread stop   is dangerous  Having said that  if you are working in a JEE environment and you have no control over the code being called  it may be necessary  see Why is Thread stop deprecated  You should never stop stop a container worker thread  If you want to run code that tends to hang   carefully  start a new daemon thread and monitor it  killing if necessary  stop   creates a new ThreadDeathError error on the calling thread and then throws that error on the target thread  Therefore  the stack trace is generally worthless  In JRE 6  stop   checks with the security manager and then calls stop1   that calls stop0    stop0   is native code  As of Java 13 Thread stop   has not been removed  yet   but Thread stop Throwable  was removed in Java 11    mailing list  JDK-8204243

[java] How do you kill a Thread in Java?

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