How to properly stop the Thread in Java

Question

I need a solution to properly stop the thread in Java   I have IndexProcessorclass which implements the Runnable interface   public class IndexProcessor implements Runnable        private static final Logger LOGGER   LoggerFactory getLogger IndexProcessor class         Override     public void run             boolean run   true          while  run                try                   LOGGER debug  Sleeping                       Thread sleep  long  15000                    LOGGER debug  Processing                  catch  InterruptedException e                    LOGGER error  Exception   e                   run   false                                     And I have ServletContextListener class which starts and stops the thread   public class SearchEngineContextListener implements ServletContextListener        private static final Logger LOGGER   LoggerFactory getLogger SearchEngineContextListener class        private Thread thread   null        Override     public void contextInitialized ServletContextEvent event            thread   new Thread new IndexProcessor             LOGGER debug  Starting thread      thread           thread start            LOGGER debug  Background process successfully started                 Override     public void contextDestroyed ServletContextEvent event            LOGGER debug  Stopping thread      thread           if  thread    null                thread interrupt                LOGGER debug  Thread successfully stopped                         But when I shutdown tomcat  I get the exception in my IndexProcessor class   2012-06-09 17 04 50 671  Thread-3  ERROR  IndexProcessor Exception java lang InterruptedException  sleep interrupted     at java lang Thread sleep Native Method      at lt ccl searchengine processor IndexProcessor run IndexProcessor java 22      at java lang Thread run Unknown Source    I am using JDK 1 6  So the question is   How can I stop the thread and not throw any exceptions    P S  I do not want to use  stop    method because it is deprecated

User · Answer

Simple answer  You can stop a thread INTERNALLY in one of two common ways    The run method hits a return subroutine  Run method finishes  and returns implicitly    You can also stop threads EXTERNALLY    Call system exit  this kills your entire process  Call the thread object s interrupt   method   See if the thread has an implemented method that sounds like it would work  like kill   or stop         The expectation is that this is supposed to stop a thread   However  what the thread actually does when this happens is entirely up to what the developer wrote when they created the thread implementation   A common pattern you see with run method implementations is a while boolean     where the boolean is typically something named isRunning  it s a member variable of its thread class  it s volatile  and typically accessible by other threads by a setter method of sorts  e g  kill     isRunnable false     These subroutines are nice because they allow the thread to release any resources it holds before terminating

User · Answer

You should always end threads by checking a flag in the run   loop  if any    Your thread should look like this   public class IndexProcessor implements Runnable        private static final Logger LOGGER   LoggerFactory getLogger IndexProcessor class       private volatile boolean execute        Override     public void run             this execute   true          while  this execute                try                   LOGGER debug  Sleeping                       Thread sleep  long  15000                    LOGGER debug  Processing                  catch  InterruptedException e                    LOGGER error  Exception   e                   this execute   false                                     public void stopExecuting             this execute   false            Then you can end the thread by calling thread stopExecuting    That way the thread is ended clean  but this takes up to 15 seconds  due to your sleep   You can still call thread interrupt   if it s really urgent - but the prefered way should always be checking the flag   To avoid waiting for 15 seconds  you can split up the sleep like this                       try               LOGGER debug  Sleeping                   for  int i   0   i  lt  150   amp  amp  this execute  i                      Thread sleep  long  100                              LOGGER debug  Processing              catch  InterruptedException e

User · Answer

Typically  a thread is terminated when it s interrupted  So  why not use the native boolean  Try isInterrupted     Thread t   new Thread new Runnable             Override         public void run                 while  Thread currentThread   isInterrupted                        do stuff                                            t start            Sleep a second  and then interrupt     try           Thread sleep 1000         catch  InterruptedException e         t interrupt      ref- How can I kill a thread  without using stop

User · Answer

Using Thread interrupt   is a perfectly acceptable way of doing this  In fact  it s probably preferrable to a flag as suggested above   The reason being that if you re in an interruptable blocking call  like Thread sleep or using java nio Channel operations   you ll actually be able to break out of those right away   If you use a flag  you have to wait for the blocking operation to finish and then you can check your flag   In some cases you have to do this anyway  such as using standard InputStream OutputStream which are not interruptable   In that case  when a thread is interrupted  it will not interrupt the IO  however  you can easily do this routinely in your code  and you should do this at strategic points where you can safely stop and cleanup   if  Thread currentThread   isInterrupted           cleanup and stop execution      for example a break in a loop     Like I said  the main advantage to Thread interrupt   is that you can immediately break out of interruptable calls  which you can t do with the flag approach

User · Answer

In the IndexProcessor class you need a way of setting a flag which informs the thread that it will need to terminate  similar to the variable run that you have used just in the class scope   When you wish to stop the thread  you set this flag and call join   on the thread and wait for it to finish   Make sure that the flag is thread safe by using a volatile variable or by using getter and setter methods which are synchronised with the variable being used as the flag   public class IndexProcessor implements Runnable        private static final Logger LOGGER   LoggerFactory getLogger IndexProcessor class       private volatile boolean running   true       public void terminate             running   false              Override     public void run             while  running                try                   LOGGER debug  Sleeping                       Thread sleep  long  15000                    LOGGER debug  Processing                  catch  InterruptedException e                    LOGGER error  Exception   e                   running   false                                     Then in SearchEngineContextListener   public class SearchEngineContextListener implements ServletContextListener        private static final Logger LOGGER   LoggerFactory getLogger SearchEngineContextListener class        private Thread thread   null      private IndexProcessor runnable   null        Override     public void contextInitialized ServletContextEvent event            runnable   new IndexProcessor            thread   new Thread runnable           LOGGER debug  Starting thread      thread           thread start            LOGGER debug  Background process successfully started                 Override     public void contextDestroyed ServletContextEvent event            LOGGER debug  Stopping thread      thread           if  thread    null                runnable terminate                thread join                LOGGER debug  Thread successfully stopped

User · Answer

For synchronizing threads I prefer using CountDownLatch which helps threads to wait until the process being performed complete  In this case  the worker class is set up with a CountDownLatch instance with a given count  A call to await method will block until the current count reaches zero due to invocations of the countDown method or the timeout set is reached  This approach allows interrupting a thread instantly without having to wait for the specified waiting time to elapse   public class IndexProcessor implements Runnable        private static final Logger LOGGER   LoggerFactory getLogger IndexProcessor class        private final CountDownLatch countdownlatch      public IndexProcessor CountDownLatch countdownlatch            this countdownlatch   countdownlatch              public void run             try               while   countdownlatch await 15000  TimeUnit MILLISECONDS                     LOGGER debug  Processing                               catch  InterruptedException e                LOGGER error  Exception   e               run   false                       When you want to finish execution of the other thread  execute countDown on the CountDownLatch and join the thread to the main thread   public class SearchEngineContextListener implements ServletContextListener        private static final Logger LOGGER   LoggerFactory getLogger SearchEngineContextListener class        private Thread thread   null      private IndexProcessor runnable   null      private CountDownLatch countdownLatch   null        Override     public void contextInitialized ServletContextEvent event            countdownLatch   new CountDownLatch 1           Thread thread   new Thread new IndexProcessor countdownLatch            LOGGER debug  Starting thread      thread           thread start            LOGGER debug  Background process successfully started                 Override     public void contextDestroyed ServletContextEvent event            LOGGER debug  Stopping thread      thread           if  countdownLatch    null                         countdownLatch countDown                       if  thread    null                try                   thread join                  catch  InterruptedException e                    LOGGER error  Exception   e                             LOGGER debug  Thread successfully stopped

User · Answer

Sometime I will try 1000 times in my onDestroy   contextDestroyed           Override     protected void onDestroy             boolean retry   true          int counter   0          while retry  amp  amp  counter lt 1000                        counter                try thread setRunnung false                   thread join                    retry   false                  thread   null    garbage can coll              catch InterruptedException e  e printStackTrace

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         threadCheckChat   new Thread new CheckUpdates         threadCheckChat start       private class CheckUpdates implements Runnable      public void run             while  shouldCheckUpdates               System out println  Do your thing here                        public void stop            shouldCheckUpdates   false

User · Answer

Some supplementary info  Both flag and interrupt are suggested in the Java doc    https   docs oracle com javase 8 docs technotes guides concurrency threadPrimitiveDeprecation html  private volatile Thread blinker   public void stop         blinker   null     public void run         Thread thisThread   Thread currentThread        while  blinker    thisThread            try               Thread sleep interval             catch  InterruptedException e                     repaint              For a thread that waits for long periods  e g   for input   use Thread interrupt    public void stop          Thread moribund   waiter        waiter   null        moribund interrupt

[java] How to properly stop the Thread in Java?

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