Concurrency / Java Thread Pools and Apache Camel - (7/250-2016)

Concurrency - is multitasking.
Camel leverages concurrency features from Java - Thread Pools

• Applications are generally bound by IO or CPU - Integration applications are generally bound by IO. Use concurrency only if applications are bound by IO
• The example below shows the usage of concurrency in Camel - default pool size is 10.
• The example can be changed with Custom Thread pools - and providing the number of threads in the pool.

Example:

<split streaming="true" parallelProcessing="true">

    <tokenize token="\n"/>

   <bean beanType="xxx.XyzService" method="testMeth"/>

</split>

• There are situations where some applications (external systems) dont allow concurrency / allow till only a certain number of concurrent messages - check SLA first.

Thread Pools

• java.util.concurrent package has the concurrency API - Java 1.5 onward.
• Clients for this api are both Camel End users and Camel as well.
• class ThreadPoolExecutor implements ExecutorService - provides thread pool with the options.
• corePoolSize
• maximumPoolSize
• keepAliveTime
• unit
• rejected
• workQueue
• threadFactory
• Managing Thread Pools
• Shutdown
• Management
• Unique Thread names
• Activity Logging
• Ensure to Use human understandable thread names

Camel & Thread pools

• Thread pools are not used directly but via configurations of thread pool profiles.
• one default profiles and multiple custom profiles
• poolSize
• maxPoolSize
• keepAliveTime
• maxQueueSize
• rejectedPolicy - Abot, CallerRuns, DiscardOldest, Discard
• CallerRuns - will use the caller thread to execute the task

Example Default Thread Pool Profile:-

<camelContext .... >

    <threadPoolProfile id="testdefaultProfile" defaultProfile="true" maxPoolSize="50"/>

</camelContext>

Example Configuring the Custom Thread Pool Profile:-

• Created using the ThreadPoolProfileSupport class -  "xyzPool" - this name will be referred later. (see pg 327 of   Camel in Action )
• Set maxPoolSize to - say 100
• register the ThreadPoolProfile to the context
• all other options will be inherited from the default profile
• in the camel route refer to the threadPool using the name "xyzPool"
• .split(...).streaming().executorServiceRef("xyzPool").bean(...)
• in spirng
• <camelContext ....> 
• <threadPoolProfile id="xyzPool" maxPoolSize="100"/>
• </camelContext>

Custom Thread Pool

• Java DSL - using ThreadPoolBuilder  (see pg 328 of   Camel in Action )
• Spring - using <threadPool> tag
• both uses the camelContext to refer to the defaultProfile as a base line

Camel will first check for Custom Thread Pool --> Custom Thread Pool Profile  --> Default

Executor Service Strategy (see pg 329 of   Camel in Action )

org.apache.camel.spi.ExecutorServiceStrategy is a pluggable API for thread pool providers.

• default - DefaultExecutorServiceStrategy - creates thread pools using concurrency API in Java
• custom - ExecutorServiceStrategy
• USECASE - Custom Camel component - and you need to run a scheduled background task - recommended to use the ScheduledExecutorService.