SEDA Component

The seda: component provides asynchronous SEDA behavior, so that messages are exchanged on a BlockingQueue and consumers are invoked in a separate thread from the producer.

Note that queues are only visible within a single CamelContext. If you want to communicate across CamelContext instances (for example, communicating between Web applications), see the VM component.

This component does not implement any kind of persistence or recovery, if the VM terminates while messages are yet to be processed. If you need persistence, reliability or distributed SEDA, try using either JMS or ActiveMQ.

Synchronous

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The Direct component provides synchronous invocation of any consumers when a producer sends a message exchange.

URI format

Where someName can be any string that uniquely identifies the endpoint within the current CamelContext.

You can append query options to the URI in the following format: ?option=value&option=value&…

Options

Name

Since

Default

Description

size

 

 

The maximum capacity of the SEDA queue (i.e., the number of messages it can hold). The default value in Camel 2.2 or older is 1000. From Camel 2.3 onwards, the size is unbounded by default. Notice: Mind if you use this option, then its the first endpoint being created with the queue name, that determines the size. To make sure all endpoints use same size, then configure the size option on all of them, or the first endpoint being created. From Camel 2.11 onwards, a validation is taken place to ensure if using mixed queue sizes for the same queue name, Camel would detect this and fail creating the endpoint.

concurrentConsumers

 

1

Number of concurrent threads processing exchanges.

waitForTaskToComplete

 

IfReplyExpected

Option to specify whether the caller should wait for the async task to complete or not before continuing. The following three options are supported: Always, Never or IfReplyExpected. The first two values are self-explanatory. The last value, IfReplyExpected, will only wait if the message is Request Reply based. The default option is IfReplyExpected. See more information about Async messaging.

timeout

 

30000

Timeout (in milliseconds) before a SEDA producer will stop waiting for an asynchronous task to complete. See waitForTaskToComplete and Async for more details. In Camel 2.2 you can now disable timeout by using 0 or a negative value.

multipleConsumers

2.2

false

Specifies whether multiple consumers are allowed. If enabled, you can use SEDA for Publish-Subscribe messaging. That is, you can send a message to the SEDA queue and have each consumer receive a copy of the message. When enabled, this option should be specified on every consumer endpoint.

limitConcurrentConsumers

2.3

true

Whether to limit the number of concurrentConsumers to the maximum of 500. By default, an exception will be thrown if a SEDA endpoint is configured with a greater number. You can disable that check by turning this option off.

blockWhenFull

2.9

false

Whether a thread that sends messages to a full SEDA queue will block until the queue's capacity is no longer exhausted. By default, an exception will be thrown stating that the queue is full. By enabling this option, the calling thread will instead block and wait until the message can be accepted.

queueSize

2.9

 

Component only: The maximum default size (capacity of the number of messages it can hold) of the SEDA queue. This option is used if size is not in use.

pollTimeout

2.9.3

1000

Consumer only – The timeout used when polling. When a timeout occurs, the consumer can check whether it is allowed to continue running. Setting a lower value allows the consumer to react more quickly upon shutdown.

purgeWhenStopping

2.11.1

false

Whether to purge the task queue when stopping the consumer/route. This allows to stop faster, as any pending messages on the queue is discarded.

queue

2.12.0

null

Define the queue instance which will be used by seda endpoint

queueFactory

2.12.0

null

Define the QueueFactory which could create the queue for the seda endpoint

failIfNoConsumers

2.12.0

false

Whether the producer should fail by throwing an exception, when sending to a SEDA queue with no active consumers.

Choosing BlockingQueue implementation

Available as of Camel 2.12

By default, the SEDA component always intantiates LinkedBlockingQueue, but you can use different implementation, you can reference your own BlockingQueue implementation, in this case the size option is not used

Or you can reference a BlockingQueueFactory implementation, 3 implementations are provided LinkedBlockingQueueFactory, ArrayBlockingQueueFactory and PriorityBlockingQueueFactory:

Use of Request Reply

The SEDA component supports using Request Reply, where the caller will wait for the Async route to complete. For instance:

In the route above, we have a TCP listener on port 9876 that accepts incoming requests. The request is routed to the seda:input queue. As it is a Request Reply message, we wait for the response. When the consumer on the seda:input queue is complete, it copies the response to the original message response.

until 2.2: Works only with 2 endpoints

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Using Request Reply over SEDA or VM only works with 2 endpoints. You cannot chain endpoints by sending to A -> B -> C etc. Only between A -> B. The reason is the implementation logic is fairly simple. To support 3+ endpoints makes the logic much more complex to handle ordering and notification between the waiting threads properly.

This has been improved in Camel 2.3 onwards, which allows you to chain as many endpoints as you like.

Concurrent consumers

By default, the SEDA endpoint uses a single consumer thread, but you can configure it to use concurrent consumer threads. So instead of thread pools you can use:

As for the difference between the two, note a thread pool can increase/shrink dynamically at runtime depending on load, whereas the number of concurrent consumers is always fixed.

Thread pools

Be aware that adding a thread pool to a SEDA endpoint by doing something like:

Can wind up with two BlockQueues: one from the SEDA endpoint, and one from the workqueue of the thread pool, which may not be what you want. Instead, you might wish to configure a Direct endpoint with a thread pool, which can process messages both synchronously and asynchronously. For example:

You can also directly configure number of threads that process messages on a SEDA endpoint using the concurrentConsumers option.

Sample

In the route below we use the SEDA queue to send the request to this async queue to be able to send a fire-and-forget message for further processing in another thread, and return a constant reply in this thread to the original caller.

Here we send a Hello World message and expects the reply to be OK.

The "Hello World" message will be consumed from the SEDA queue from another thread for further processing. Since this is from a unit test, it will be sent to a mock endpoint where we can do assertions in the unit test.

Using multipleConsumers

Available as of Camel 2.2

In this example we have defined two consumers and registered them as spring beans.

Since we have specified multipleConsumers=true on the seda foo endpoint we can have those two consumers receive their own copy of the message as a kind of pub-sub style messaging.

As the beans are part of an unit test they simply send the message to a mock endpoint, but notice how we can use @Consume to consume from the seda queue.

Extracting queue information.

If needed, information such as queue size, etc. can be obtained without using JMX in this fashion:

See Also

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