Create a scheduler

Create a scheduler that manages execution of deferred tasks. It takes as input a runnable object, a string as the name of the task. It must support

• Starting a thread identified by name based on a future time provided
• Canceling a thread based on its name

Solution

• Use a min heap to keep track of objects, keys being the time
• Use a dispatch thread to monitor if the top of heap is ready for execution
• This thread sleeps for a time between now and time at the top of heap
• When woken up, it extracts the top of heap, checks if its valid or cancelled (use a hash for state)
• It processes the object, then removes from queue
• When a new object is inserted check if the new object landed at top of heap, if it did then interrupt the dispatch thread and adjust its sleep time accordingly