How to design an execution engine for a sequence of tasks

Question

I am trying to code a problem in Java where I have to execute a bunch of tasks.

Problem

Execute a job which consists of multiple tasks and thos

Answer 1

2 options in terms of pattern usage, but in essence they are pretty similar. In either cases, cyclic dependencies situation need to be handled as a error in task dependency configuration. e.g. A -> B -> A

1. Mediator pattern

After each task[i] finishes, it will notify the Mediator, the the Mediator will notify all successor tasks of task[i]. The graph of task dependencies will be read when the execution engine starts as the data structure for Mediator to use.

2. Publish/Subscribe pattern via message bus.

The graph of task dependencies will be read as the engine starts, and each task will subscribe to MessageBus of its predecessor task's (task[i]) message of completion on topic[i]

When each task[i] finishes, it will send completion message to the MessageBus in topic[i]. Each task who subscribes to topic[i] will get notified and starts to work.