TASK MANAGER

Explanation to all decisions provided in the comments to the code. This is the simplest way to explain the idea behind each and every decision.

Key points

1. Top level interface for the user is a TaskManager class which has the following methods:

   1. TaskManager.add - Add new process based on command and priority into the system.
   2. TaskManager.kill - Terminate process based on process descriptor returned by TaskManager.add function.
   3. TaskManager.kill_group - Terminate all processes in the system based on priority.
   4. TaskManager.kill_all - Terminal all processes in the system.

2. TaskManager.add function returns instance of Process class which shall be considered as a descriptor. Interface allows getting access to all key fields without.

3. User can call Process.kill and TaskManager will be notified about this. Such approach allows much safer resource management.

4. Constructor of TaskManager accepts different type of Storage which would change behavior of TaskManager.add interface depending on what is needed. Basically this allows extensibility of the solution. Also simplifies testing after a new feature is added.

5. PID wrapped into a separate class with PID.value property. In case something (type of PID) has to be changed no major impact is required.

6. Process ID (PID) generated based on UUID1 which would guarantee uniqueness.

7. Primary data structure to store collection of Process objects is dictionary (Hashmap). As there are many requirements there is no data structure which would satisfy all in optimal way. In some cases PriorityQueue or Queue can be used to have optimal implementation of TaskManager.list function but then TaskManager.kill would suffer. At the end the trade-off is to have O(1) insertion and deletion complexity (add, kill) and O(n) on TaskManager.list.

8. Build time is simulated by python import with environment variable.

Run instructions

Entry point to the project will main.py in the root folder. This file contains set of usage examples for TaskManager. In order to run it you would need python3 installed on your system and execute:

python3 main.py

With python2 you most likely will see invalid syntax exception. This solution doesn't use anything which is not available in python2 except richer syntax for type declaration. So, it's easier for reader to understand what type of data expected on input and output of each function.