Threads

How can I decouple the continued routing of a message from the current thread?

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Submit the message to a thread pool, which then is responsible for the continued routing of the message.

In Camel, this is implemented as the Threads EIP.

Options

The Threads eip supports 11 options, which are listed below.

Name Description Default Type

description

Sets the description of this node.

String

disabled

Whether to disable this EIP from the route during build time. Once an EIP has been disabled then it cannot be enabled later at runtime.

false

Boolean

executorService

To use a custom thread pool.

ExecutorService

poolSize

Sets the core pool size.

Integer

maxPoolSize

Sets the maximum pool size.

Integer

keepAliveTime

Sets the keep alive time for idle threads.

Long

timeUnit

Sets the keep alive time unit. By default SECONDS is used.

Enum values:

  • NANOSECONDS

  • MICROSECONDS

  • MILLISECONDS

  • SECONDS

  • MINUTES

  • HOURS

  • DAYS

TimeUnit

maxQueueSize

Sets the maximum number of tasks in the work queue. Use -1 or Integer.MAX_VALUE for an unbounded queue.

Integer

allowCoreThreadTimeOut

Whether idle core threads are allowed to timeout and therefore can shrink the pool size below the core pool size Is by default false.

false

Boolean

threadName

Sets the thread name to use.

Threads

String

rejectedPolicy

Sets the handler for tasks which cannot be executed by the thread pool.

Enum values:

  • Abort

  • CallerRuns

ThreadPoolRejectedPolicy

callerRunsWhenRejected

Whether or not to use as caller runs as fallback when a task is rejected being added to the thread pool (when its full). This is only used as fallback if no rejectedPolicy has been configured, or the thread pool has no configured rejection handler. Is by default true.

true

String

Using Threads EIP

The example below will add a Thread pool with a pool size of five threads before sending to mock:result.

  • Java

  • XML

from("seda:a")
  .threads(5)
  .to("mock:result");
<route>
    <from uri="seda:a"/>
    <threads poolSize="5"/>
    <to uri="mock:result"/>
</route>

And to use a thread pool with a task queue of only 20 elements:

  • Java

  • XML

from("seda:a")
  .threads(5).maxQueueSize(20)
  .to("mock:result");
<route>
    <from uri="seda:a"/>
    <threads poolSize="5" maxQueueSize="20"/>
    <to uri="mock:result"/>
</route>

And you can also use a thread pool with no queue (meaning that a task cannot be pending on a queue):

  • Java

  • XML

from("seda:a")
  .threads(5).maxQueueSize(0)
  .to("mock:result");
<route>
    <from uri="seda:a"/>
    <threads poolSize="5" maxQueueSize="0"/>
    <to uri="mock:result"/>
</route>

About rejected tasks

The Threads EIP uses a thread pool which has a worker queue for tasks. When the worker queue gets full, the task is rejected.

You can customize how to react upon this using the rejectedPolicy and callerRunsWhenRejected options. The latter is used to easily switch between the two most common and recommended settings. Either let the current caller thread execute the task (i.e. it will become synchronous), but also give time for the thread pool to process its current tasks, without adding more tasks (self throttling). This is the default behavior.

The Abort policy, means the task is rejected, and a RejectedExecutionException is thrown.

The reject policy options Discard and DiscardOldest is deprecated in Camel 3.x and removed in Camel 4 onwards.

Default values

The Threads EIP uses the default values from the default Thread Pool Profile. If the profile has not been altered, then the default profile is as follows:

Option Default Description

poolSize

10

Sets the default core pool size (minimum number of threads to keep in pool)

keepAliveTime

60

Sets the default keep-alive time (in seconds) for inactive threads

maxPoolSize

20

Sets the default maximum pool size

maxQueueSize

1000

Sets the default maximum number of tasks in the work queue. Use -1 for an unbounded queue.

allowCoreThreadTimeOut

true

Sets default whether to allow core threads to timeout

rejectedPolicy

CallerRuns

Sets the default handler for tasks which cannot be executed by the thread pool. Has four options: Abort, CallerRuns, Discard, DiscardOldest which corresponds to the same four options provided out of the box in the JDK.

See Also

See Threading Model

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