Correctly implementing IJobsQueueService

[kumards]

Fix for #4718. IJobsQueueService supposed to be just a service than an event handler.

[sebastienros]

Why? Isn't the solution to fix the bug in the event bus? That would be a non-breaking change this way.

[kumards]

Yeah, this fix solved my problem. I believe by mistake IJobsQueueService inherited IEventHandler instead of IDependency.

[sebastienros]

No, it's by design, on purpose that it's an IEventHandler, but there is a bug in event handlers, which needs to be fixed, c.f. linked issues. I am closing this PR, please create one that fixes the event handler, it should be explained in this one: #4584

[kumards]

Does that mean, there can be multiple implementations of IJobsQueueService?

I guess if IJobsQueueServiceis going to inherit from IEventHandler, then it has to be injected like collection IEnumerable<IJobsQueueService> jobsQueueServices, not as a single instance.

[sfmskywalker]

Although technically speaking one could of course create multiple implementations, you don't inject an enumerable, but a single instance. This baffled me too at first. Check this out for more details (including the comments): http://www.ideliverable.com/blog/ieventhandler

[kumards]

I am just curious, why is it intentionally inheriting from IEventHandler when multiple implementations of it is not expected?

[sfmskywalker]

The reason is that this enables other modules to use the IJobsQueueService without having to actually add a project reference to Orchard.JobsQueue. This is actually a very nice pattern to implement modules with truly optional dependencies, where the dependent module would still build even if there was no Orchard.JobsQueue available. The only sad part is the poor choice of name, because to your point, IEventHandler would indicate a handler of an event or events. I wouldn't be surprised if this will be renamed in O2, or if at least an additional interface with a more appropriate name will be provided that leverages the same event bus in the same way.