Exceptions in WebBackgroundWorker when cleaning previously hanged tasks

[alexbudarov]

Environment

• Platform version: 6.8.12
• Client type: Web

Description of the bug or enhancement

During workload testing, test server was hung for >30 mins because of database locks.
After I have killed all conflicting connections, server continued to work.
But in the log started to appear many error messages (new error every 5 seconds), stacktraces below:

Click to expand

2018-09-21 11:59:00,853 ERROR [cuba_web_backgroundScheduler-1] [o.s.s.support.TaskUtils$LoggingErrorHandler] Unexpected error occurred in scheduled task.
com.vaadin.ui.UIDetachedException: null
        at com.vaadin.ui.UI.access(UI.java:1452)
        at com.haulmont.cuba.web.gui.executors.impl.WebBackgroundWorker$WebUIAccessor.access(WebBackgroundWorker.java:419)
        at com.haulmont.cuba.gui.executors.impl.TaskHandlerImpl.kill(TaskHandlerImpl.java:190)
        at com.haulmont.cuba.gui.executors.impl.TaskHandlerImpl.closeByTimeout(TaskHandlerImpl.java:183)
        at com.haulmont.cuba.gui.executors.impl.TasksWatchDog.cleanupTasks(TasksWatchDog.java:69)
        at sun.reflect.GeneratedMethodAccessor1644.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at org.springframework.scheduling.support.ScheduledMethodRunnable.run(ScheduledMethodRunnable.java:65)
        at org.springframework.scheduling.support.DelegatingErrorHandlingRunnable.run(DelegatingErrorHandlingRunnable.java:54)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
        at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)
2018-09-21 11:59:05,854 ERROR [cuba_web_backgroundScheduler-1] [o.s.s.support.TaskUtils$LoggingErrorHandler] Unexpected error occurred in scheduled task.
com.vaadin.ui.UIDetachedException: null
        at com.vaadin.ui.UI.access(UI.java:1452)
        at com.haulmont.cuba.web.gui.executors.impl.WebBackgroundWorker$WebUIAccessor.access(WebBackgroundWorker.java:419)
        at com.haulmont.cuba.gui.executors.impl.TaskHandlerImpl.kill(TaskHandlerImpl.java:190)
        at com.haulmont.cuba.gui.executors.impl.TaskHandlerImpl.closeByTimeout(TaskHandlerImpl.java:183)
        at com.haulmont.cuba.gui.executors.impl.TasksWatchDog.cleanupTasks(TasksWatchDog.java:69)
        at sun.reflect.GeneratedMethodAccessor1644.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:498)
        at org.springframework.scheduling.support.ScheduledMethodRunnable.run(ScheduledMethodRunnable.java:65)
        at org.springframework.scheduling.support.DelegatingErrorHandlingRunnable.run(DelegatingErrorHandlingRunnable.java:54)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
        at java.util.concurrent.FutureTask.runAndReset(FutureTask.java:308)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:180)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:294)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
        at java.lang.Thread.run(Thread.java:748)

These messages continue to appear every 5 seconds even 12 minutes after first one.