1. Virtual memory, parallel programming Jakub Yaghob
Computer skills
Virtual memory, parallel programming
Jakub Yaghob

2. Process Process Program executed by OS Code, data, current activity
Private address space

3. Physical Address Space
Virtual memory
Process security
Work with more memory than available
Virtual Address
Space
Physical Address Space
Address Translation

4. Virtual memory – paging
VAS/PAS divided to the blocks of the same size – pages/frames
Translation converts a page number to a frame number
Translation may not exist – page miss
Present bit
Page tables
One level
Multiple levels
Zero level

5. Virtual memory – paging
Virtual address 31 12 11
Page number (PN)
Offset
Page table
[0]
flags
Physical address
[1] 31 12 11
GLUE
Frame number (FN)
Offset
[PN-1]
[PN] FN
[PN+1]
[MAXPN]

6. Multitasking, multiprocessing
Multiple processes running simultaneously on OS
Multiprocessing
Multiple CPUs in one computer

7. Thread Thread Multiple activities in one process Starting thread
Private stack for each thread
Local variables, parameters, chain of function calls
Context

8. Memory organization Code Constants Initialized static data
Uninitialized static data
Heap
Stack for thread n
Stack for thread 1

9. Race condition Race condition
The output is dependent on sequence or timing of other uncontrollable events
Preemptive scheduling
type PRec = ^TRec; TRec = record val:integer; next:Prec; end; var list:PRec; C
next D
nil
list

10. Race condition Initial state Correct state Incorrect state
Thread 1
InsertList(Ap);
procedure InsertList(node:PRec);
begin
node^.next:=list;
list:=node;
end;
Thread
InsertList(Bp);
Initial state
list X Y
Correct state
Incorrect state A
list B A X Y
list X Y
Another correct state B
list A B X Y