`ThreadPoolTaskExecutor` Threads are not killed after execution in Spring

it seems you create a thread pool in the same size of exams which is not quite optimal.

    // Core pool size is = number of exams  
    threadPoolExecuter.setCorePoolSize(lstOfExams.size());

    // Max pool size is just 1 + exam size. 
    threadPoolExecuter.setMaxPoolSize(lstOfExams.size()+1);

You have to consider that: - If you create a thread pool and started it as many threads as defined in core size started immediately.

• The max pool size is only than effective when you submit more than core pool threads can process right now AND when the queue size is full (in this case 100). So that means a new thread will be only then created when the number of submitted tasks exceeded 100+exam size.

In your case I would set the core pool size 5 or 10 (it actually depends on the how many core your target CPU have and/or how IO bound the submitted tasks are).

The max pool size can be double of that but it doesn't effective until the queue is full.

To let the size of live threads decrease after the submitted work done you have to set 2 parameters.

• setKeepAliveSeconds(int keepAliveSeconds) : Which let the threads shut down automatically if they are not used along the defined seconds (by default 60 seconds, which is optimal) BUT this is normally only used to shut down threads of non-core pool threads.

• To shut down threads of core part after keepAliveSeconds you have to set setAllowCoreThreadTimeOut(boolean allowCoreThreadTimeOut) as true. Which is normally false to keep core pool alive as long as the application is running.

I hope it helps.

I suspect that one of your threads waits indefinitely for an IO request answer. For example, you try to connect to a remote host where you did not set connection timeout and the host does not answer. In this case, you can shutdown all executing tasks forcefully by running shutdownNow method of the underlying ExecutorService then you can analyze InterruptedIOException thrown by the offending threads.

Replace

threadPoolExecuter.shutdown();

with below so you can examine errors.

ExecutorService executorService = threadPoolExecuter.getThreadPoolExecutor();
executorService.shutdownNow();

This will send interrupt signal to all running threads.

The threads do not wait on IO from some remote server, because the executed method on the threads would be in some jdbc driver classes, but they are currently all in UpdateUserExamDataThread.run(), line 37.

Now the question is: what is the code at UpdateUserExamDataThread.java line 37 ? Unfortunately, the UpdateUserExamDataThread.java given at the moment is incomplete and/or not the version really executed: the package declaration is missing and it ends at line 29.

I suspect the issue is simply that you are calling run() instead of execute() when spawning the task thread using submit(). There is probably some expectation when using submit that threads kill themselves when the task is finished rather than terminating at the end of the run method.

Just Needed to increase the priority of threads and create number of threads as per number of cores in processor.

protected void executeInternal(JobExecutionContext context) throws JobExecutionException {
        logger.error("Result Processing executed");
        List<Object[]> lstOfExams = examService.getExamEntriesForProcessingResults();
        String timeZone = messageService.getMessage("org.default_timezone", null, Locale.getDefault());
        int cores = Runtime.getRuntime().availableProcessors();
        if(lstOfExams!=null&&!lstOfExams.isEmpty()){
            ThreadPoolTaskExecutor threadPoolExecuter = new ThreadPoolTaskExecutor();
            threadPoolExecuter.setCorePoolSize(cores);
//          threadPoolExecuter.setMaxPoolSize(Integer.MAX_VALUE);
            threadPoolExecuter.setBeanName("ThreadPoolTaskExecutor");
//          threadPoolExecuter.setQueueCapacity(Integer.MAX_VALUE);
            threadPoolExecuter.setQueueCapacity(lstOfExams.size()+10);
            threadPoolExecuter.setThreadNamePrefix("ThreadForUpdateExamResult");
            threadPoolExecuter.setWaitForTasksToCompleteOnShutdown(true);
            threadPoolExecuter.setThreadPriority(10);
            threadPoolExecuter.initialize();


            for(Object[] obj : lstOfExams){
                if(StringUtils.isNotBlank((String)obj[2]) ){
                    timeZone = obj[2].toString();
                }
                try {
                    Userexams userexam=examService.findUserExamById(Long.valueOf(obj[0].toString()));
                    if(userexam.getExamresult()==null){
                        UpdateUserExamDataThread task=new UpdateUserExamDataThread(obj,timeZone,testEvaluator);
//                      threadPoolExecuter.submit(task);
                        threadPoolExecuter.execute(task);
                    }
//                  testEvaluator.generateTestResultAsPerEvaluator(Long.valueOf(obj[0].toString()), obj[4].toString(), obj[3]==null?null:obj[3].toString(),timeZone ,obj[5].toString() ,obj[1].toString()); 
//                  logger.error("Percentage Marks:::::"+result.getPercentageCatScore());
                } catch (Exception e) {
                    logger.error("Exception at ResultProcessingJob extends QuartzJobBean executeInternal(JobExecutionContext context) throws JobExecutionException",e);
                    continue;
                }
            }
                threadPoolExecuter.shutdown();
        }
}