Timeout-based task interruption is implemented by the WatchDog bean. To ensure that it is invoked periodically, you should add the following declaration to the spring.xml files of the Web Client *and *Desktop Client blocks:

<bean id="backgroundWorkerScheduler" class="org.springframework.scheduling.concurrent.ThreadPoolTaskScheduler">
    <property name="daemon" value="true"/>
    <property name="poolSize" value="1"/>
</bean>

<task:scheduled-tasks scheduler="backgroundWorkerScheduler">
    <task:scheduled ref="cuba_BackgroundWorker_WatchDog" method="cleanupTasks" fixed-delay="2000"/>
</task:scheduled-tasks>

In the Web Client block task state polling is initiated by the client code running in web-browser. Polling interval is defined by the cuba.backgroundWorker.uiCheckInterval application property; the default value is 2 seconds.