The GenericObjectPool is configured for 12 Threads. Once 12 threads are exhausted, I find the caller thread goes zombie. I think default behaviour is to enqueue extra requests and serve once available instead of killing caller thread.

Code:
private ImplClass implObject;

for (Iterator iter = anArrayList.iterator(); iter.hasNext();) {

    //Gets a GenericObjectPool Object
    implObject = (ImplClass) this.getImplPool().borrowObject();

    some code

}
I have tried both configurations as below for configuring pool. For me blocking is fine so long as it resumes from borrow statement and process lines below it inside loop.

Code:
<bean id="ImplPool" class="org.apache.commons.pool.impl.GenericObjectPool">
    <constructor-arg>
        <ref local="ImplFactory"/>
    </constructor-arg>
    <constructor-arg>
        <value>12</value>
    </constructor-arg>    
</bean> 



<bean id="ImplPool" class="org.apache.commons.pool.impl.GenericObjectPool">
    <constructor-arg>
        <ref local="ImplFactory"/>
    </constructor-arg>
    <constructor-arg>
        <value>12</value>
    </constructor-arg>    
<constructor-arg>
         <bean id="org.apache.commons.pool.impl.GenericObjectPool.WHEN_EXHAUSTED_BLOCK" 
         class="org.springframework.beans.factory.config.FieldRetrievingFactoryBean" />
    </constructor-arg>      
<constructor-arg>
        <value>-1</value>
    </constructor-arg>
</bean>
Can you please suggest a config for a blocking GenericObjectPool on reaching threshold ?