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 to the producer.
Note that queues are only visible within a single CamelContext. If you want to communicate across CamelContext instances such as to communicate across 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 then try using either JMS or ActiveMQ.
Synchronous
The Direct component provides synchronous invocation of any consumers when a producer sends a message exchange.
URI format
seda:someName[?options]
Where someName can be any string to uniquely identify the endpoint within the current CamelContext.
Same URI must be used for both producer and consumer
The excact same Seda endpoint URI must be used for both the producer and consumer. Otherwise Camel will create a 2nd Seda endpoint even thought that someName
part of the URI is identical. For example:
from("direct:foo").to("seda:bar?concurrentConsumers=5"); from("seda:bar?concurrentConsumers=5").to("file://output");
Notice that we have to use the full URI including options in both the producer and consumer.
Options
Name |
Default |
Description |
---|---|---|
size |
1000 |
The maximum size of the SEDA queue |
concurrentConsumers |
1 |
Camel 1.6.1/2.0: Number of concurrent threads processing exchanges. |
waitForTaskToComplete |
IfReplyExpected |
Camel 2.0: Option to specify if the caller should wait for the async task to be complete or not before continuing. The following 3 options is supported: Always, Newer or IfReplyExpected. The first two options is self explained. The last will only wait if the message is Request Reply based. The default option is IfReplyExpected. See more information about Async messaging. |
timeout |
30000 |
Camel 2.0: Timeout in millis a seda producer will at most waiting for an async task to complete. See |
Changes in Camel 2.0
In Camel 2.0 the Seda component supports using Request Reply where the caller will wait for the Async route to complete. For instance:
from("mina:tcp://0.0.0.0:9876?textline=true&sync=true").to("seda:input"); from("seda:input").to("bean:processInput").to("bean:createResponse");
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 its a Request Reply message we will wait for the response. So when the consumer on the seda:input
queue is complete it will copy this response to the original message as response.
Camel 1.x does not have this feature implemented, the Seda queues in Camel 1.x will newer wait.
Concurrent consumers
By default Camel uses a single consumer. You can configure the endpoint to use concurrent consumers. So instead of thread pools you can use:
from("seda:stageName?concurrentConsumers=5").process(...)
Difference between thread pools and concurrent consumers
The thread pool is a pool that dynamically can increase/shrink at runtime depending on load, the concurrent consumers is always fixed.
Thread pools
Be aware that adding a thread pool to a seda endpoint by doing something like:
from("seda:stageName").thread(5).process(...)
can wind up with two BlockQueues. One from seda endpoint and one from the workqueue of the thread pool which may not be what you want. Instead, you might want to consider configuring a Direct endpoint with a thread pool which can process messages both synchronously and asynchronously. For example:
from("direct:stageName").thread(5).process(...)
You can also directly configure number of threads that process messages on seda endpoint using concurrentConsumers
parameter.
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 an unit test it will be sent to a mock endpoint where we can do assertions in the unit test.