What is required

• Simulating operating system’s virtual memory management and concurrency control

• Processes must be simulated as threads

• The simulated system has two CPUs (or CPU cores) ➔ 2 processes must be selected instead of 1

• Main memory should be simulated as an array (size = number of pages) in your program !

• Disk pages should be simulated in an external file

• Virtual memory manager should be simulated as a separate thread as well

• For the scheduler you can use the one implemented in the last assignment (In case you have not finished assignment #2 you can work with a FIFO scheduler)

Simulating the Processes

• For each process you create a thread corresponding to it --> Do not create multiple threads for each process !

• Each thread (simulated process) should call the exposed VMM API services (Store, Release and Lookup) accordingly

• Each process should continually call a command from the list of commands (commands.txt).

• You can simulate the process to wait for a random time (from 1 to 1000 milliseconds for example) between each API call

Simulating the VMM

• Should be simulated as a thread as well • Implements the basic services :

– Store a variable

– Release a variable – Lookup a variable

• Variables can be either in – The main memory

– The disk

• Lookup might involve swapping the variable first before returning it

• The VMM is running on its own thread (same as the scheduler in previous assignment)

Simulating the VMM

• The VMM class:

Class VMM {

VMM (size);

Store (string variableId, unsigned int value); Release (string variableId) ;

Lookup (string variableId) ; }

Simulating the VMM- VMM Constructor

• VMM (size):

• Initializes a VMM with the given size for the main memory.

• size = the size specified in the memconfig.txt file

Simulating the VMM – Store, Release, Lookup

• Store (string variableId, unsigned int value):

– Stores the given variable id and its value into the main memory array, if there is a free space. Otherwise, it stores them into the vm.txt file

• Release (string variableId):

• Removes the variable id and its value from the memory so the page which was holding this variable becomes available for further storage

• First check if the variable exists in main memory then delete it. Otherwise check if it exists in the vm.txt file then delete it.

• Lookup (string variableId):

•         If (variableId exists in main memory){ then return value;

}

else if (variableId exists in Disk) {

if(spot is available in main memory){

then move variable into main memory

and release assigned page in virtual memory }

else{

Check for the variable with the smallest Last time access in main memory

Swap with this variable }

} else{

return -1 (variable doesn’t exist) }