Unbalanced Parallel Task Scheduler

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Difficulty

Reading material

Create a task scheduler that is parameterized in the number of threads to use. Let’s call this parameter thread_count.

The scheduler should divide the given lists of tasks in thread_count sublists of (approximately) equal size. Next, it should fire up thread_count threads and give each thread one of these sublists.

We say this scheduler is unbalanced because, although the tasks are distributed evenly, it is possible that some tasks involve more work than others. For example, there could be an unlucky thread that gets 10× the work of the others: it would have to trudge on alone. A balanced scheduler would have the other threads come to its aid.

Implement the task scheduler described above. Make it available through a factory function

TaskScheduler unbalanced_parallel(unsigned thread_count);

1. Evaluation

Create a script that takes at least 20 seconds to render.
Render it using the unbalanced parallel scheduler, using 1..N threads, where N is the number of logical cores your machine has. Keep track of the rendering times.
Make a little graph (e.g., in Excel) that shows how rendering times change with the number of threads.