Disruptor Component

Available as of Camel 2.12

The disruptor: component provides asynchronous SEDA behavior much as the standard SEDA Component, but utilizes a Disruptor instead of a BlockingQueue utilized by the standard SEDA.

Alternatively, a disruptor-vm: endpoint is supported by this component, providing an alternative to the standard VM.

As with the SEDA component, buffers of the disruptor: endpoints are only visible within a single CamelContext and no support is provided for persistence or recovery. The disruptor-vm: endpoints provides support for communication across CamelContexts instances (provided camel-disruptor.jar is on the system/boot classpath).

The main advantage of choosing to use the Disruptor Component over the SEDA or the VM Component is performance in use cases where there is high contention between producer(s) and/or multi-casted or concurrent consumers. In those cases, significant increases of throughput and reduction of latency has been observed. Performance in scenarios without contention is comparable to the SEDA and VM Components.

The Disruptor is implemented with the intention of mimicking the behavior and options of the SEDA and VM Components as much as possible.

The main differences are:

• The buffer used is always bounded in size (default 1024 exchanges).
• As a the buffer is always bounded, the default behavior for the Disruptor is to block while the buffer is full instead of throwing an exception. This default behavior may be configured on the component (see options).
• Disruptor endpoints don't implement the BrowsableEndpoint interface. As such, the exchanges currently in the Disruptor can't be retrieved, only the number of exchanges.
• Disruptor requires its consumers (multicasted or otherwise) to be statically configured. Adding or removing consumers on the fly requires complete flushing of all pending exchanges in the Disruptor.
• As a result of the reconfiguration: data sent over a Disruptor is directly processed and 'gone' if there is at least one consumer. Late joiners receive new exchanges published after they joined.
• The pollTimeout option is not supported by the Disruptor Component.
• When a producer blocks on a full Disruptor, it does not respond to thread interrupts.

Maven users will need to add the following dependency to their pom.xml for this component:

<dependency>
    <groupId>org.apache.camel</groupId>
    <artifactId>camel-disruptor</artifactId>
    <version>x.x.x</version>
    <!-- use the same version as your Camel core version -->
</dependency>

URI Format

 disruptor:someName[?options]

or

 disruptor-vm:someName[?options]

Where someName can be any string that uniquely identifies the endpoint within the current CamelContext (or across contexts in case of disruptor-vm:).

You can append query options to the URI in the following format:

?option=value&option=value&...

Options

All the following options are valid for both the disruptor: and disruptor-vm: components:

Wait strategies

The wait strategy effects the type of waiting performed by the consumer threads that are currently waiting for the next exchange to be published. The following strategies can be chosen:

Use of Request Reply

The Disruptor 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("disruptor:input");

from("disruptor: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 disruptor:input buffer. As it is a Request Reply message, we wait for the response. When the consumer on the disruptor:input buffer is complete, it copies the response to the original message response.

Concurrent consumers

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

from("disruptor:stageName?concurrentConsumers=5")
  .process(...)

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 and supported by the Disruptor internally so performance will be higher.

Threadpools

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

from("disruptor:stageName")
  .thread(5)
  .process(...)

Can wind up with adding a normal BlockingQueue to be used in conjunction with the Disruptor, effectively negating part of the performance gains achieved by using the Disruptor. Instead, it's recommended to directly configure the number of threads that process messages on a Disruptor endpoint using the concurrentConsumers option.

Sample

In the route below we use the Disruptor to send the request to this asynchronous 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.

public void configure() throws Exception {
    from("direct:start")
        // send it to the disruptor that is async
        .to("disruptor:next")
        // return a constant response
        .transform(constant("OK"));

    from("disruptor:next")
      .to("mock:result");
}

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

Object out = template.requestBody("direct:start", "Hello World");
assertEquals("OK", out);

The Hello World message will be consumed from the Disruptor 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

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

<!-- define the consumers as spring beans -->
<bean id="consumer1" class="org.apache.camel.spring.example.FooEventConsumer"/>

<bean id="consumer2" class="org.apache.camel.spring.example.AnotherFooEventConsumer"/>

<camelContext xmlns="http://camel.apache.org/schema/spring">
    <!-- define a shared endpoint which the consumers can refer to instead of using url -->
    <endpoint id="foo" uri="disruptor:foo?multipleConsumers=true"/>
</camelContext>

Since we have specified multipleConsumers=true on the Disruptor foo endpoint we can have those two or more 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.

Note the use of @Consume to consume from the Disruptor.

public class FooEventConsumer {

    @EndpointInject(uri = "mock:result")
    private ProducerTemplate destination;

    @Consume(ref = "foo")
    public void doSomething(String body) {
        destination.sendBody("foo" + body);
    }

}

Extracting disruptor Information

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

DisruptorEndpoint disruptor = context.getEndpoint("disruptor:xxxx");
int size = disruptor.getBufferSize();