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Camel leverages thread pools in the following places:

• several EIP patterns supports using thread pools for concurrency
• SEDA component for asynchronous connectivity
• Threads DSL in the Camel route
• ServicePool for pooling services
• And some component provide thread pools by nature such as JMS, Jetty

Thread pool profiles

By default when a thread pool is to be created then its based on the default thread pool profile which is:

    <threadPoolProfile id="defaultThreadPoolProfile" defaultProfile="true"
                       poolSize="10" maxPoolSize="20" maxQueueSize="1000" allowCoreThreadTimeOut="false"
                       rejectedPolicy="CallerRuns"/>

What that means is that for example when you use Multicast with parallelProcessing=true enabled, then it would create a thread pool based on the profile above. The rejectedPolicy have has four options: Abort, CallerRuns, Discard, DiscardOldest which corresponds to the same four options provided out of the box in the JDK. Notice: option allowCoreThreadTimeOut is a new option from Camel 2.15 onwards.

You can define as many thread pool profiles as you like. But there must only one default profile. A custom thread pool profile will inherit from the default profile. Which means that any option you do not explicit define will fallback and use the option from the default profile.

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Suppose you want to use a custom thread pool profile for a Multicast EIP pattern in a Camel route you can do it using the executorServiceRef attribute as shown:

<camelContext ...>
    ...
    <threadPoolProfile id="fooProfile" 
                       poolSize="20" maxPoolSize="50" maxQueueSize="-1"/>
    ...

    <route>
       ...
       <multicast strategyRef="myStrategy" executorServiceRef="fooProfile">
          ...
       </multicast>
      ...
    <route>
</camelContext>

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The default pattern is for:

• Camel 2.9.x or older: Camel (${camelId}) thread #${counter} - ${name}
• Camel 2.10 onwards: Camel (#camelId#) thread ##counter# - #name#

Notice we renamed the tokens from Camel 2.10 onwards to not clash with tokens by the Property Placeholder.

In the pattern you can use the following placeholders

• ${camelId} Camel 2.6: is the CamelContext name
• ${counter} is a unique incrementing counter.
• ${name} is the regular thread name.
• ${longName} is the long thread name which can includes endpoint parameters etc.

Notice the pattern name has changed from Camel 2.10 onwards, use #name# instead.

In Camel 2.11 onwards its easier to set the thread name pattern on the CamelContext using the threadNamePattern attribute in the XML files as shown below:

  <camelContext xmlns="http://camel.apache.org/schema/spring" threadNamePattern="Riding the thread #counter#">
    <route>
      <from uri="seda:start"/>
      <to uri="log:result"/>
      <to uri="mock:result"/>
    </route>
  </camelContext>

Component developers

If you develop your own Camel component and are in need of a thread pool, then its advised to use the ExecutorServiceStrategy/ExecutorServiceManager to create the thread pool you need.

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All thread pools created by Camel will be properly shutdown when CamelContext shutdowns which ensures no leaks in the pools in case you run in a server environment with hot deployments and the likes.

The ExecutorServiceManager has APIs for shutting down thread pools graceful and aggressively. Its encourage to use this API for creating and shutting down thread pools.

From Camel 2.11 onwards Camel the graceful shutdownGraceful(executorService) method from ExecutorServiceManager will shutdown graceful at first, until a timeout value is hit. After that it shutdown aggressively, again using the timeout value to wait for the operation to complete. This means you can wait at most 2 x timeout for shutting down the thread pool.
The timeout value is by default 10000 millis. You can configure a custom value on the ExecutorServiceManager if needed. During shutdown Camel will log every 2nd second at INFO level progress of shutting down the thread pool. For example in case a shutdown takes a while, then there is activity in the logs.

The APIs on ExecutorServiceManager that is related to shutting down a thread pool is as follows:

See Also

• Architecture
• Async