Task Dependency Scheduler

You are given a set of tasks, each identified by a unique name or integer. Some tasks depend on others, meaning that a task can only be executed once all of its dependencies have been completed. The input will be provided as a list of pairs, where each pair is in the format (task, dependency), meaning that the dependency must be completed before task can begin. Note that a task may have multiple dependencies, and some tasks may not depend on any other tasks.

Your task is to write a function that:

1. Accepts the list of tasks and their dependencies.
2. Determines an execution order for the tasks that respects the dependency requirements.
3. Returns an ordering (list) of tasks such that each task appears after all of its dependencies.
4. If it is impossible to determine such an ordering due to a cycle in the dependencies, the function should return an empty list (or an appropriate error indicator).

Consider the efficiency of your solution. Your implementation should handle a reasonable number of tasks and dependencies.

Write your solution in your preferred programming language and ensure it includes tests or examples that demonstrate your function works for both acyclic dependency graphs and cases where a cycle exists.