Use of java.util.concurrent.Executor stops tomcat from stopping

Question

Background:

I need to use java.util.concurrent.Executor to serialize the execution of some legacy code inside a WebService.

I have added an member variable, executor, to the WebService class. It is injected from the outside by the springframework.

The executor bean is defined as such:

<bean id="riskValueEstimateUpdateExecutor" scope="singleton"
        class="java.util.concurrent.Executors"
        factory-method="newSingleThreadExecutor" />

• Tomcat version: 6.0.22
• Java version: 1.6
• spring framework: 2.5.5

Problem:

The WS works as expected. We rolled it out to a linux server. Then we realised the tomcat stop script could no longer stop the service.

I use kill -3 to the tomcat instance. In the thread dump I find these lines:

"pool-2-thread-1" prio=10 tid=0xad637c00 nid=0xf37 waiting on condition [0xae882000..0xae883020]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0xb453b710> (a java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject)
        at java.util.concurrent.locks.LockSupport.park(LockSupport.java:158)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject.await(AbstractQueuedSynchronizer.java:1925)
        at java.util.concurrent.LinkedBlockingQueue.take(LinkedBlockingQueue.java:358)
        at java.util.concurrent.ThreadPoolExecutor.getTask(ThreadPoolExecutor.java:946)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:906)
        at java.lang.Thread.run(Thread.java:619)

How can I fix this problem?

If you need more information, please suggest.

Answer 1

It's neither Tomcat's nor Spring's fault. You just have to shutdown ExecutorService properly. Add destroy-method in bean definition:

<bean id="riskValueEstimateUpdateExecutor" scope="singleton"
    class="java.util.concurrent.Executors"
    factory-method="newSingleThreadExecutor" destroy-method="shutdown"/>

BTW singleton scope is default. You might also consider using shutdownNow() method. Also note that Spring provides powerful task scheduling mechanism.

Answer 2

You need to find a way to call shutdown when the Spring context is shutdown: try using the bean destroy-method property and set that to shutdown. Something like this:

<bean id="riskValueEstimateUpdateExecutor" scope="singleton"
        class="java.util.concurrent.Executors"
        factory-method="newSingleThreadExecutor" destroy-method="shutdown" />