`ThreadPoolTaskExecutor` Threads are not killed after execution in Spring

Question

I am trying to change Quartz Sequential execution to Parallel Execution.

It is working fine, Performance wise, it is seems good but Spawned (created) threads are not destroyed.

It is Still in Runnable State; why and How can I fix that? Please Guide me.

Code is here :

    @Override
    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());
        if(lstOfExams!=null&&!lstOfExams.isEmpty()){
            ThreadPoolTaskExecutor threadPoolExecuter = new ThreadPoolTaskExecutor();
            threadPoolExecuter.setCorePoolSize(lstOfExams.size());
            threadPoolExecuter.setMaxPoolSize(lstOfExams.size()+1);
            threadPoolExecuter.setBeanName("ThreadPoolTaskExecutor");
            threadPoolExecuter.setQueueCapacity(100);
            threadPoolExecuter.setThreadNamePrefix("ThreadForUpdateExamResult");
            threadPoolExecuter.initialize();

            for(Object[] obj : lstOfExams){
                if(StringUtils.isNotBlank((String)obj[2]) ){
                    timeZone = obj[2].toString();
                }
                try {
                    Userexams userexams=examService.findUserExamById(Long.valueOf(obj[0].toString()));
                    if(userexams.getExamresult()==null){
                        UpdateUserExamDataThread task=new UpdateUserExamDataThread(obj,timeZone);
                        threadPoolExecuter.submit(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) {
                    Log.error("Exception at ResultProcessingJob extends QuartzJobBean executeInternal(JobExecutionContext context) throws JobExecutionException",e);
                    continue;
                }

            }
            threadPoolExecuter.shutdown();
        }
}

UpdateUserExamDataThread .class

@Component
//@Scope(value="prototype", proxyMode=ScopedProxyMode.TARGET_CLASS)
//public class UpdateUserExamDataThread extends ThreadLocal<String> //implements Runnable {
public class UpdateUserExamDataThread implements Runnable {
    private Logger log = Logger.getLogger(UpdateUserExamDataThread.class);
    @Autowired
    ExamService examService;
    @Autowired
    TestEvaluator testEvaluator;
    private Object[] obj;
    private String timeZone;


    public UpdateUserExamDataThread(Object[] obj,String timeZone) {
        super();
        this.obj = obj;
        this.timeZone = timeZone;
    }

    @Override
    public void run() {
        String threadName=String.valueOf(obj[0]);
        log.info("UpdateUserExamDataThread Start For:::::"+threadName);
        testEvaluator.generateTestResultAsPerEvaluator(Long.valueOf(obj[0].toString()), obj[4].toString(), obj[3]==null?null:obj[3].toString(),timeZone ,obj[5].toString() ,obj[1].toString());
        //update examResult
        log.info("UpdateUserExamDataThread End For:::::"+threadName);
    }

}

TestEvaluatorImpl.java

@Override
    @Transactional
    public Examresult generateTestResultAsPerEvaluator(Long userExamId, String evaluatorType, String codingLanguage,String timeZoneFollowed ,String inctenceId ,String userId) {
        dbSchema = messageService.getMessage("database.default_schema", null, Locale.getDefault());

        try {
//Some Methods
return examResult;
}catch(Exception e){
log.erorr(e);
}
}

I can provide Thread Dump file if needed.

Answer 1

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.