Is it possible to give a custom scope to a direct channel? (no subscriber issue)

[davidcyp]

Hello,

I have the following requirement:
- each simulation must run on a dedicated thread (which must be the same thread for all consecutive simulations with the same id)

Therefore I have implemented a custom scope (which works fine), called simulation scope. Spring creates an instance per value for that scope. Eg.

@Scope("simulation")
public class Foo { .. }

When the value for my scope is set to simulation-1, I'll get an instance of Foo, eg. Foo-1. When the value for scope is set to simulation-2 , it results in a new instance of Foo, eg. Foo-2. When yet another message contains scope simulation-1, the instance Foo-1 is reused. This all works fine.

Some information about my integration setup:

My requests contain a simulation-id and a security-token. When a request enters the system, the request is spawned to a new thread. A ThreadLocal containing the security information is attached to the thread. Security is applied. So far, so good.

After the security check is passed, my requests for a given simulation(depending on the simulation-id in the header), should be executed on the SAME dedicated thread for THAT given simulation-id.

Eg. simulation-1 messages should always be executed on sim-exec-thread-1, and simulation-2 messages should always be executed on sim-exec-thread-2.

I have tried to accomplish this by using the following construct:

  
<integration:channel id="singleThreadedSimulationChannel">
  <integration:dispatcher task-executor="dedicatedSingleThreadedTaskExecutor"/>
</integration:channel>

<!-- poolsize = ! : this fulfills my requirement; messages are moved to the SAME dedicated thread.. 
       However, HOW do I create such a SCOPED dedicated thread.. 
-->
<bean id="dedicatedSingleThreadedTaskExecutor"
        class="org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor" scope="simulation">
  <property name="corePoolSize" value="1"/>
  <property name="maxPoolSize" value="1"/>
  <property name="threadNamePrefix" value="Sim-Exec-Thread-"/>
</bean>

With the code above, my messages for simulation-2 are handled by the same thread thus the thread for simulation-1. I tried to solve this by setting the scope for singleThreadedSimulationChannel to scope="simulation". However, this results in the dreaded message "dispatcher has no subscribers".

Note that all my other code eg. ServiceActivators are also scoped to scope="simulation", and they work fine. The only problem I have regarding scope is when I try to move the messages from their individual threads to a dedicated thread (which should be dedicated, per scope, thus one instance per scope eg. one instance for scope-value=simulation-1 and one instance for scope-value=simulation-2)

Does anyone has a clue how to solve this?
Thanks in advance,
David

[davidcyp]

I've managed to find a partial solution. I now have an instance of my serviceActivator(EchoService) per simulation. But I am still searching for a way to have a DEDICATED thread per simulation.

@Component
@Scope( "game" )
public class ScopedThreadPoolTaskExecutor extends ThreadPoolTaskExecutor {
  
  private static final int CORE_POOL_SIZE = 1;
  private static final int MAX_POOL_SIZE = 1;

  public ScopedThreadPoolTaskExecutor() {
    super();
    setCorePoolSize( CORE_POOL_SIZE );
    setMaxPoolSize( MAX_POOL_SIZE );
  }
}

and

<integration:channel id="singleThreadedSimulationChannel">
  <integration:dispatcher task-executor="scopedThreadPoolTaskExecutor"/>
</integration:channel>

solved the problem.

For completeness of the example; this is my serviceActivator definition

<integration:service-activator input-channel="singleThreadedSimulationChannel" output-channel="outChannel"
                                 ref="echoService"/>

There where my previous solution always pointed to the same instance of my serviceActivator(EchoService), the new solution points to an instance per simulation.

Eg. log output before changes:

DEBUG[Sim-Exec-Thread-1] org.acme.EchoService - ## instance = org.acme.EchoService@150382b5
DEBUG[Sim-Exec-Thread-1] org.acme.EchoService - ## message = Message for simulation 2

DEBUG[Sim-Exec-Thread-1] org.acme.EchoService - ## instance = org.acme.EchoService@150382b5
DEBUG[Sim-Exec-Thread-1] org.acme.EchoService - ## message = Mensaje para simulation 3

DEBUG[Sim-Exec-Thread-1] org.acme.EchoService - ## instance = org.acme.EchoService@150382b5
DEBUG[Sim-Exec-Thread-1] org.acme.EchoService - ## message = Mensaje 2 para simulation 3

DEBUG[Sim-Exec-Thread-1] org.acme.EchoService - ## instance = org.acme.EchoService@150382b5
DEBUG[Sim-Exec-Thread-1] org.acme.EchoService - ## message = Other message for simulation 2

vs. log output after changes:

DEBUG[Sim-Exec-Thread-1] org.acme.EchoService - ## instance = org.acme.EchoService@702b4b78
DEBUG[Sim-Exec-Thread-1] org.acme.EchoService - ## message = Message for simulation 2

DEBUG[Sim-Exec-Thread-1] org.acme.EchoService - ## instance = org.acme.EchoService@7abbf606
DEBUG[Sim-Exec-Thread-1] org.acme.EchoService - ## message = Mensaje para simulation 3

DEBUG[Sim-Exec-Thread-1] org.acme.EchoService - ## instance = org.acme.EchoService@7abbf606
DEBUG[Sim-Exec-Thread-1] org.acme.EchoService - ## message = Mensaje 2 para simulation 3

DEBUG[Sim-Exec-Thread-1] org.acme.EchoService - ## instance = org.acme.EchoService@702b4b78
DEBUG[Sim-Exec-Thread-1] org.acme.EchoService - ## message = Other message for simulation 2

They are still all on Sim-Exec-Thread-1, but other instances are handling the messages, based on their simulation-id. Note that I can verify this because the EchoService also writes the message in the database for the given simulation. This way, I can assure myself that the code works as desired.

However, one problem remains: HOW do I move execution of the messages to a DEDICATED thread per simulation?

[davidcyp]

Adding some randomness to my code, clarified that different threads are used. It seems that, for every instance, my ThreadPoolExecutor bean starts counting from zero.

Thus:

instance1 spawns a new thread, the first and only for this this instance, with name Sim-Exec-Thread-1.
instance2 spawns a new thread the first and only for this this instance, with name Sim-Exec-Thread-1.

While they share the same name, they are not the same threads.

Problem solved.

[oleg.zhurakousky]

I was just thinking about this and there is probably a simpler solution we can do within the framework itself.
Would you mind opening a JIRA https://jira.springsource.org/browse/INT

[davidcyp]

Done, see https://jira.springsource.org/browse/INT-2654

[Mark Fisher]

Did you try adding the "scope" attribute to the channel itself? It seems like that fits your use-case (and your question).

[davidcyp]

Yes Marc, I did. It resulted in a "dispatcher has no subscribers" error. Sidenote: When the application starts, all beans are instantiated in an invalid scope, which I defaulted to SCOPE_NO_SIMULATION_STARTED. Then, when my first simulation starts, a message enters the system, with a simulation-id of eg SIM-1. This instantiates the beans in the correct scope. I think it might be related to the fact that the beans that get created when the application context is starting, are not used throughout the application because they are in a scope which is never used.

[Mark Fisher]

I don't fully understand the reason for creating the "invalid scope". Are you using aop:scoped-proxy? (the idea is that a proxy exists which can lazily be "filled" when the necessary scope is active). As long as you are sending Messages only after a scope is activated, you should be able to satisfy your use-case with the "scope" attribute on a channel.

[davidcyp]

I don't use scoped-proxy. We (ab)use the "invalid scope" for some integration tests, but not in production code.

[oleg.zhurakousky]

David

Sorry, I am just getting to this issue and i have a question.
Would it be true to say that your message caries or may carry some unique data that can be used to determine which thread to use?