java - Application hangs for few minutes even after all the threads are done -

i converted working producer/consumer example thread/runnable executor/callable/blockingqueues , using poison pill termination pattern.

if run program below, hang few minutes though every thread has completed. jstack shows numerous threads blocked on queue not seemingly related application.

"pool-1-thread-10" prio=5 tid=10b08d000 nid=0x10d91c000 waiting on condition [10d91b000]    java.lang.thread.state: timed_waiting (parking)     @ sun.misc.unsafe.park(native method)     - parking wait  <7f3113510> (a java.util.concurrent.synchronousqueue$transferstack)     @ java.util.concurrent.locks.locksupport.parknanos(locksupport.java:198)     @ java.util.concurrent.synchronousqueue$transferstack.awaitfulfill(synchronousqueue.java:424)     @ java.util.concurrent.synchronousqueue$transferstack.transfer(synchronousqueue.java:323)     @ java.util.concurrent.synchronousqueue.poll(synchronousqueue.java:874)     @ java.util.concurrent.threadpoolexecutor.gettask(threadpoolexecutor.java:945)     @ java.util.concurrent.threadpoolexecutor$worker.run(threadpoolexecutor.java:907)     @ java.lang.thread.run(thread.java:680) 

i can not figure out why application hangs. appreciated. thank you

import java.util.arraylist; import java.util.collection; import java.util.list; import java.util.random; import java.util.concurrent.callable; import java.util.concurrent.executionexception; import java.util.concurrent.executorservice; import java.util.concurrent.executors; import java.util.concurrent.future; import java.util.concurrent.linkedblockingqueue;  public class producersconsumers {     private linkedblockingqueue<item> queue = new linkedblockingqueue<item>();     private static final executorservice executorpool = executors.newcachedthreadpool();     private random randgenerator = new random(system.currenttimemillis());      private class item {         private boolean done = false;         private string message;          private item(boolean done) {             this.done = done;         }          private item(string message) {             this.message = message;         }          public boolean isdone() {             return done;         }          public string getmessage() {             return message;         }     }      private class producer implements callable<long> {         private final int id;         private integer numofmessages;          private producer(int id, int numofmessages) {             this.id = id;             this.numofmessages = numofmessages;         }          @override         public long call() throws exception {             long totaltime = 0;             while (numofmessages > 0) {                 string message;                 synchronized (numofmessages) {                     long starttime = system.nanotime();                     int msglength = randgenerator.nextint(20000);                     stringbuilder sb = new stringbuilder(msglength);                     (int = 0; < msglength; a++) {                         sb.append((char) ('a' + randgenerator.nextint(26)));                     }                     message = sb.tostring();                     long endtime = system.nanotime();                     totaltime += endtime - starttime;                 }                 numofmessages--;                 queue.put(new item(message));             }             system.out.println("-------------producer " + id + " done.");             queue.put(new item(true));             return totaltime;         }     }      private class consumer implements callable<long> {         private string monitor = "monitor";         private final int id;          private consumer(int id) {             this.id = id;         }          @override         public long call() throws exception {             long totaltime = 0;             while (true) {                 item item = queue.take();                 if (item.isdone()) {                     break;                 }                 synchronized (monitor) {                     long starttime = system.nanotime();                     stringbuilder sb = new stringbuilder(item.getmessage());                     sb = sb.reverse();                     string message = sb.tostring();                     long endtime = system.nanotime();                     totaltime += endtime - starttime;                 }             }             system.out.println("+++++++++++++consumer " + id + " done.");             return totaltime;         }     }      public void begin(int threadcount) throws interruptedexception, executionexception {         collection<producer> producers = new arraylist<producer>();         (int = 0; < threadcount; i++) {             producers.add(new producer(i, randgenerator.nextint(5)));         }         collection<consumer> consumers = new arraylist<consumer>();         (int = 0; < threadcount; i++) {             consumers.add(new consumer(i));         }         try {             long starttime = system.nanotime();             list<future<long>> producerfuturelist = executorpool.invokeall(producers);             list<future<long>> consumerfuturelist = executorpool.invokeall(consumers);             long producertotaltime = 0;             long consumertotaltime = 0;              (future<long> future : producerfuturelist) {                 producertotaltime += future.get();             }             (future<long> future : consumerfuturelist) {                 consumertotaltime += future.get();             }             long mainthreadtotaltime = system.nanotime() - starttime;              system.out.println("producertotaltime   " + producertotaltime);             system.out.println("consumertotaltime   " + consumertotaltime);             system.out.println("mainthreadtotaltime " + mainthreadtotaltime);             system.out.println("difference          " + (producertotaltime + consumertotaltime - mainthreadtotaltime));         } catch (interruptedexception e) {             e.printstacktrace();  //to change body of catch statement use file | settings | file templates.             throw e;         } catch (executionexception e) {             e.printstacktrace();  //to change body of catch statement use file | settings | file templates.             throw e;         }      }      public static void main(string[] args) throws executionexception, interruptedexception {         producersconsumers prodcon = new producersconsumers();         prodcon.begin(20);     } } 

you should close executorservice when done it. call executorpool.shutdown() @ end of program.