[[ThreadingModel-ThreadingModel]]
= Threading Model

*Since Camel 2.3*

The threading model in Camel is based on leveraging the JDK concurrency
API which provides thread pools, named `ExecutorService`.

Camel leverages thread pools in the following places:

* several xref:{eip-vc}:eips:enterprise-integration-patterns.adoc[EIP] patterns supports using thread pools for
concurrency
* xref:components::seda-component.adoc[SEDA] component for asynchronous connectivity
* xref:async.adoc[Threads DSL] in the Camel route
* And some component provide thread pools by nature such as
xref:components::jms-component.adoc[JMS], xref:components::jetty-component.adoc[Jetty]

[[ThreadingModel-Threadpoolprofiles]]
== Thread pool profiles

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

[source,xml]
--------------------------------------------------------------------------------------------------------
    <threadPoolProfile id="defaultThreadPoolProfile" defaultProfile="true"
                       poolSize="10" maxPoolSize="20" maxQueueSize="1000" allowCoreThreadTimeOut="true"
                       rejectedPolicy="CallerRuns"/>
--------------------------------------------------------------------------------------------------------

NOTE: From Camel 3.4 onwards the default thread pool profile has `allowCoreThreadTimeOut=true` while
it was `allowCoreThreadTimeOut=false` in older Camel versions.

What that means is that for example when you use
xref:{eip-vc}:eips:multicast-eip.adoc[Multicast] with `parallelProcessing=true` enabled,
then it would create a thread pool based on the profile above. The
`rejectedPolicy` 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.

You can use `-1` in maxQueueSize to indicate a unbounded queue.

In Java DSL you can configure the default thread pool profile from the
`ExecutorServiceStrategy`/`ExecutorServiceManager` which you access from
`CamelContext`.

[[ThreadingModel-Usingthreadpoolprofiles]]
== Using thread pool profiles

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:

[source,xml]
---------------------------------------------------------------------------
<camelContext ...>
    ...
    <threadPoolProfile id="fooProfile" 
                       poolSize="20" maxPoolSize="50" maxQueueSize="-1"/>
    ...

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

What Camel will do at runtime is to lookup in the
xref:registry.adoc[Registry] for a `ExecutorService` with the id =
fooProfile. If none found it will fallback and see if there is a
`ThreadPoolProfile` defined with that id. And in this example there is
and so the profile is used for creating a new `ExecutorService` which is
handed back to the xref:{eip-vc}:eips:multicast-eip.adoc[Multicast] EIP to use in the
route.

[[ThreadingModel-Createcustomthreadpool]]
== Create custom thread pool

You can also use the <threadPool/> tag in Spring XML to create a
specific thread pool (eg `ExecutorService`). Notice that any options you
do not explicit define, will have Camel to use the default thread pool
profile as fallback. For example if you omit setting the `maxQueueSize`
then Camel will fallback and use the value from the default thread pool
profiles, which by default is 1000.

[[ThreadingModel-Management]]
== Management

All the thread pools that Camel creates are managed and thus you can see
them in JConsole under the `threadpools` category.

[[ThreadingModel-ExecutorServiceStrategy]]
== ExecutorServiceStrategy

*Since Camel 2.3 to 2.8.x* +
 Camel provides a pluggable strategy to hook in your own thread pool
provider, for example from a WorkManager in a J2EE server etc. +
 See the `org.apache.camel.spi.ExecutorServiceStrategy` interface which
you should implement and hook into the WorkManager.

See
xref:advanced-configuration-of-camelcontext-using-spring.adoc[Advanced
configuration of CamelContext using Spring] for how to configure it.

You can configure it on the `CamelContext` from Java DSL using the
getter/setter.

[[ThreadingModel-ExecutorServiceManager]]
== ExecutorServiceManager

*Since Camel 2.9*

In camel 2.9.0 the `ExecutorServiceManager` replaces the
`ExecutorServiceStrategy`. It is renamed to manager as is not only
provides a strategy for thread pool creation but also keeps track of
thread pools and thread pool profiles.

To hook in custom thread pool providers (e.g. for J2EE servers) a
`ThreadPoolFactory` interface can be implemented. The implementation can
be set in the `ExecutorServiceManager`. The Factory interface is much
simpler then the former `ExecutorServiceStrategy` and makes the job of
integrators much easier.

See
xref:advanced-configuration-of-camelcontext-using-spring.adoc[Advanced
configuration of CamelContext using Spring] for how to configure it.

[[ThreadingModel-Customizingthreadnames]]
== Customizing thread names

On the `ExecutorServiceStrategy`/`ExecutorServiceManager` you can
configure the thread name pattern using the `setThreadNamePattern`
method, which defines the thread names used when a thread pool creates a
thread.

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 xref:using-propertyplaceholder.adoc[Property Placeholder].

In the pattern you can use the following placeholders

* $\{camelId} *Camel 2.6:* is the xref:camelcontext.adoc[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:

[source,xml]
--------------------------------------------------------------------------------------------------------------
  <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>
--------------------------------------------------------------------------------------------------------------

[[ThreadingModel-Componentdevelopers]]
== 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.

[[ThreadingModel-Shutdown]]
== Shutdown

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:

[width="100%",cols="25%,75%",options="header"]
|===
|Method |Description

|shutdown |Marks the thread pool as shutdown, eg just as calling
`ExecutorService.shutdown()` method

|shutdownNow |Forces the thread pool to shutdown now, eg just as calling
`ExecutorService.shutdownNow()` method

|shutdownGraceful |*Camel 2.11:* Marks the thread pool as shutdown, and graceful shutdown
the pool, by waiting for tasks to complete. A default timeout value of
10 sec is used, before 
 shutdown becomes aggressive using `shutdownNow`, to force threads to
shutdown.

|shutdownGraceful(timeout) |*Camel 2.11:* As above but with custom timeout value

|awaitTermination |*Camel 2.11:* To wait graceful for the termination of a thread pool (eg
to wait for its tasks to complete). Will wait until all tasks is
completed or a timeout value is hit.
|===

