Camel Split/RecipientList Threads & Transaction Boundaries - apache-camel

Question

In Apache Camel 2.20.2, I created a route with a split() and recipientlist(). I would like the entire route and recipients of each Exchange to occur in the same transaction. I am confused about when Camel will use a separate thread and transaction boundary. I've read through the Camel documentation and combed through various articles/forums on the web. I am looking for a definitive answer.
In Camel I have this route:
from("seda:process")
.transacted("TRANS_REQUIRESNEW")
.to("sql:classpath:sql/SelForUpdate.sql?dataSource=DataSource1")
.split(body())
.shareUnitOfWork()
.setHeader("transactionId", simple("${body.transactionId}"))
// Datasource 2 updates happening using "direct:xxxx" recipients
.recipientList().method(Routing.class).shareUnitOfWork().end()
.to("sql:classpath:sql/UpdateDateProcessed.sql?dataSource=DataSource1");
In the Spring context I defined the transaction management:
<jee:jndi-lookup expected-type="javax.sql.DataSource" id="Datasource1" jndi-name="jdbc/Datasource1"/>
<jee:jndi-lookup expected-type="javax.sql.DataSource" id="Datasource2" jndi-name="jdbc/Datasource2"/>
<bean id="datasource1TxManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
<property name="dataSource" ref="Datasource1" />
</bean>
<bean id="datasource2TxManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
<property name="dataSource" ref="Datasource2" />
</bean>
<bean id="TRANS_REQUIRESNEW"
class="org.apache.camel.spring.spi.SpringTransactionPolicy">
<property name="transactionManager">
<bean id="txMgrRouting"
class="org.springframework.data.transaction.ChainedTransactionManager">
<constructor-arg>
<list>
<ref bean="datasource1TxManager" />
<ref bean="datasource2TxManager" />
</list>
</constructor-arg>
</bean>
</property>
<property name="propagationBehaviorName"
value="PROPAGATION_REQUIRES_NEW" />
</bean>
When I run the route, it appears that the updates to Datasource1 and Datasource2 are happening in separate transactions. In addition, it appears the SelForUpdate.sql and UpdateDateProcessed.sql for Datasource1 are happening in separate transactions.
My question is, where are new threads created in this code, and where are the transaction boundaries? How would I get this to happen in one transaction context?
In reading the Apache Camel Developer's Cookbook, I understand the Split and RecipientList patterns both use the same thread for all processing (unless parallel processing is used). With the SpringTransactionPolicy beans that I've created, it seems all work in this route and recipient routes should take place in the same transaction context. Am I correct?