Operating System Simulation: Virtual Memory and Process Scheduling

The main objective of this assignment is to simulate operating system’s virtual memory management, process scheduling and concurrency/synchronization control as discussed during the Lab sessions.

The following features should be considered for this simulation:

1- Processes should be simulated by threads in the application. Each process has a starting time and duration (burst time). “processes.txt” is the input file which contains the number of processes N followed by N lines. Each line contains the process start time and duration.

2- Process Scheduler: A process scheduling thread should be implemented based on the “Round Robin” policy that schedules the processes as discussed during the lab sessions. In this assignment (#3) we assume that the simulated system has two CPUs (or CPU cores). Therefore, two processes can be executed at the same time, i.e. the scheduler must select two processes (from the head of the waiting queue) for execution during each cycle. Additionally, the time slice must be set to 3000 ms.(Alternatively we can use FIFO as specified in the tutorial!)

3- Virtual Memory Management: Virtual memory consists of a fixed size main memory and unlimited disk space. The main memory is divided into frames while the virtual memory is divided into pages. A page has the same size as a frame. The size of the main memory will be given as an input in a file called “memconfig.txt”. This file contains a number indicating number of frames in main memory. The disk space is assumed to be unlimited. Notice that frames in the main memory should be simulated by an array (or vector) in the actual computer physical memory, while virtual memory pages are simulated by an array stored in a text file such as “vm.txt”, which must be accessed every time we need to access the disk space.

4- Processes try to store, release and retrieve “variables” to/from the memory. Each page contains only one variableId and its value. Of course, working with memory can only happen when the process is running. Each variable in the memory has a Last Access property which is a time stamp indicating the last time this variable was accessed.

5- Virtual memory manager should be implemented with a set of APIs (functions) as follows:

a. memStore (string variableId, unsigned int value): This instruction stores the given variableId and its value in the first unassigned spot in the memory.

b. memFree (string variableId): This instruction removes the variableId and its value from the memory, so the page which was holding this variable becomes available for storage.